I agree with the chorus of people who noticed the dripping left fuel injector. That may be THE issue. A strobe or timing light will help you see the spray fan more clearly. (The right injector looked good BTW.) Also, the EGR valve is shot. It should hold the vacuum and cause stumbling at idle. Although it's not causing the idle problem, it's never going to open because the rubber diaphragm is split. Also, the vacuum to the EGR valve should increase when throttle increases. Can't wait for the next installment of this series, Ivan. You have the best auto mechanics channel on the Internet! (Sorry Scotty.)
@@PineHollowAutoDiagnostics I hear you there. I have Saturn Astra belongs to a Viet Nam vet. I am doing all the work for free. The ECM replacement install is driving me crazy. LOL Even with a TECH 2!
@@PineHollowAutoDiagnostics At least you have live data on that vehicle. All I have is flashing light codes on mine. 88 Isuzu 2.3 I-TEC. Doesn't know whether to be rich, lean or correct each time you start it. So I am setting up to make a break out box for the computer. An eight channel pico would be nice here but only have two 2ch lab scopes and three DMMs.. Going to monitor injector pulse width, O2, MAF, B+@ECM, grounds@ECM, injector modulation pulse from the distributor, engine coolant temp sensor and fuel pressure. The car has good days and bad days so I will get to see both. When I do this maybe I'll send you a picture of the total hook up just for poo and laughter as Eric would say.
Had to do this on my 1989 Mazda MPV 2.6L. The MAF was a bit skewed...fixed that one with an in-line resistor on the signal wire. Still working fine 10 years later!!!
I m a fleet mechanic. I know its hard to do otherwise. When we pierce a wire, I find that in about three years that wire will oxidize at the point of fail. Not so much in the cabin, but in the engine compartment it will. I find this in our vehicles. Even when you think it stays clean. Your great to watch and Im always learning. Thanks.
"Have you ever seen injectors firing on a Throttle Body" Yes I have. Is that injector dripping fuel at 25:03 ? The fuel should be a steady stream and atomizing in the venturi.
@@NoWr2Run The early Volvo's had that system on some of their cars. I can tell you that is the way they worked. They called it a single point injector on a 4 cylinder engine.on a 1.8 and 2.0 engine. First time i have seen 2 injectors on the throttle body .
Since the injectors can be unplugged separately I would try unplugging them independently and looking at idle mixture at O2 sensor as well as block and integrator. Do this for each injector. Just a thought. You and Eric O the absolute best on YT!
My thoughts exactly. I'd check for vacuum leaks as well. There are so many variables going on here. It's case where you have do the process of elimination to deal with all the variables. Diags like this can be a real pain. But when you do figure it out, it'll bring out your best. I've been through running issues similar to this in the past. I've seen sometimes it can literally take days or even weeks to figure this out. Have a merry Christmas and happy new year.
Exactly right, Paul. One variable at a time, via the path of least resistance. Takes time, patience, and lots of note-taking and trust in your diagnostic tools :)
Pine Hollow Auto Diagnostics my friend, old cars are hard to fix since there are not many pids to go by. The logic of the ECM is base on few sensors! As you said too many variables! But it is fun!!
@@PineHollowAutoDiagnostics these 89s and 90s trucks drove many a man to drinking., thats why so many parts get replaced on them, because everything is somehow connected, and symptoms can be very similar. if the parts werent plentiful and cheap, these trucks would be extinct! great when running good but when they act up, you better get you a snickers.
Hey MotoYam Excellent Test checking for the 1 wire o2 sensor. Seen that ground loss many times. GM started putting a separate ground wire soldered on the o2s for there 366 big blocks truck motors. Really enjoyed your theory. For someone who doesn't do this for a living like I do. Youved done well.👍👍
Hi Richard, thank you for the comment! I really thought I was on to something, but that ground was near perfect! Oh well, that just makes it more interesting ;)
Ivan. I have had the same exact problem with my 1992 c1500. When I bought it the engine was bad. Mine was originally a 305 and that’s what I replaced it with. Now I got a used engine. The standings on the block were that of a TBI 305. I later found out that the cylinder heads were 081 heads and from my research were likely from a TPI engine. Now I also noticed my overall engine vacuum was lower than it should be. I checked all external leaks, none found. I tried a different intake manifold I had with the same results. Doing some more tease arch I found the base timing for the TPI engine was 7*BTDC, not the 0* of the TBI set up. Now I mentioned the low vacuum I was measuring it at 15” of mercury. Once I advanced the timing to 7* it brought the vacuum up to 20”. There was also another difference between the two cylinder head setups. That was the heat range of the spark plugs. I changed to the hotter plugs of the TPI head and between the two changes my idle issue when warm in closed loop idle was much better. My block learn values went from 102-103 to about 120 or so. Though this information may not solve this trucks problems it did for mine. Please also note that I did every check you have done so far. Additionally I did try a different computer and a different prom. Something you may want to look at prom related is a tab for driveway stall out on these trucks which was supposed to be solved with an updated prom. If this helps great. If not I hope you find this trucks problem. As always great videos and I look forward to hopefully many more!
Thanks for the info, David! It's crazy how many hidden variables there are on these "old school" TBI systems! Had no idea what I was getting into with this truck haha
@@PineHollowAutoDiagnostics I mentioned this in the first video; i find it odd that your vacuum is so low - verify the map sensor compared to manifold pressure at idle.
n3lee Yes good suggestion. I did when I was diagnosing my trucks problem. I am lucky enough to have another TBI truck that runs awesome so in addition to comparing the pids for the map sensors with the engines at the same operating temperatures I was able to swap in the “know good” sensor to the truck that was not running well and the results were the same. Low vacuum at hot idle.
if you put a timing light behind the throttle body pointed at the injectors you can see the patterns pretty good. Nice series Ivan thanks for your time.. Merry Christmas
Man, this one's got me scratching my head! There's nothing like a good Christmas mystery though! Kudos to your thought processes, Ivan. I can almost see the wheels in your brain working. I too was noticing the spray pattern coming out of that one injector. I can't wait for the next installment to see if it's related! Get this one fixed, and the borscht and vodka's on me!
You can check injector spray pattern with your timing light(while you are checking ignition timing),point the light at each injector and it will freeze pattern. Should be no drips.Check prom and calpack numbers that are on each against list for proper application in old G.M. parts catalog.
It's been so long since I've seen/had one of these, my head is already swimming. You ARE right though... Keep returning to the basics. Like going from tubes to solid state, the principles remain the same. Only the checks and balances become tighter...
I can't get this thought out of my head: The Chevy 305, 327, and 350 were the SAME ENGINE! Stoke and bore were the only difference. A minor difference in carb jetting, but EVERYTHING else was the same...
You know you have to get some waveforms on those dual peak injectors while you have them together with a PICO! I've been hoping to run across some with my Hantek for a while now.
Ivan interesting study. I watched the first video. AND now this one. I would call it too high psi on the fuel pump as it's not designed for this type of engine. But maybe bad injector. Will wait to see part 3. :) can't walt lol
He'll get it, and it'll spin heads at it's simplicity. Going from a 305, to a 350 was an extremely minor change back in those days. The fact that it was changed MAY be the cause of confusion. Pretend is is ALL original and go from there. These dinasours were NOT as complicated as multi port...etc. Pretend it still runs on a carb!
When you stopped and went back to diagnose it again acting as if you had no prior knowledge was stunning. It's what we all need to remember about problems, I know that when thinking about cars or any problems I get caught in a loop then throw the parts cannon at it: be cars or life. I have watched a couple thousand RUclips videos dealing with cars too mowers and that idea to back up has never been said. Sensory overload. Thanks that's another tool for me to remember.
Yeah sensory overload for sure! My mind often gets carried away with all the info and possibilities. One of the hardest parts of problem solving is keeping the thoughts organized, and designing very specific experiments to have a clear answer to every fork in the road. Might take some time, but in most cases it gets to the answer more efficiently and accurately :)
This may seem a little far fetched but check the ignition module. I have had quite a few that had similar symptoms. It relies on a signal from the distributor to generate a fuel pulse. You have covered about Everything else. Helps if you had a spare distributor assembly to give it a shot. There is a tan and black striped wire under the dash to unplug. Set initial ignition timing to 0 degrees no more no less. Plug said wire back in. Just had a lot of experience with these trucks lol. Some models said wire was under the hood by the heater core under a plastic cover where the fuel pump relay lives. Hope this helps!
not sure when he replaced the injectors if he point new ones in at time of engine swap looks like one side is duping more like its not performing well … I would check fuel flow and also fuel pressure ,, yep my next step would be fuel delivery and pressure ...great content and its fun to watch your diagnostics steps,, great job
If the base idle could not be controlled without messing with screws then suspect a bad throttle body gasket. Especially if iac counts are pegged low.More air equals more fuel.
loving this as i drive a 94 silverado 5.7 tbi .... i have headers with long tube the o2 is in the collector on left bank ..no problems .. ive been lead to believe that compression and cam can also cause running problems .. is it a tbi engine thats in the truck ... generic crate motor is not compatable ... just another line of thought ... lots of great comments here ... and a lot of interest for good ole truck ... was the last tbi truck ivan fixed for the rev it guy at the scrap yard .... is the map vac line on the right fitting one is a breather ..also check for tbi mods jb weld ect gadjet man groove ..looking forward to part 3 ..
I understand your frustrations my friend.i have seen on some old small block Chevy's were intake manifold gaskets have simtoms similar to what u are experiencing.and it's always when engine comes up to warmer temperature when this occurred.its a possibility.guess smoking it out when it's nice n warm might Chase t problem out.i have also seen t base of the throttle body draw vacuum were t butterfly plates join at the throttle rod.
Throttle Body Gasket at back is notorious for blowing out a small section. Will elevate idle from a little to 1200 rpm. Of course Map senses it. Also check thermal air door in air filter housing snout. Supposed to open from exhaust temp but foil tube always gets chunked. Also don’t overlook base timing. Usually sets at zero plus/minus couple degrees.
Gotta love them old OBD1 GM vehicles...(pre 1995/95) they were one of the rare ones to give out a datastream. I still have an old Snap-On MTG2500 scanner I use for the old stuff...always comes in clutch for an oddball issue on an older GM!
@@PineHollowAutoDiagnostics I love my old brick! I've got al lthe adapters for all the hot mess back then for Chrysler, Jeep, Ford, Toyota, Nissan and whatnot for American and Japanese vehicles...shop has a newer Solus series scanner for OBD2 stuff...but the older stuff...out comes the 2500 and lemme tell ya, I'm not gettin rid of it any time soon! Too handy...way too handy.
Dash display had grounding issues, was an issue with that generation. Ask me how I know. Failed intake gaskets are common on these engines as well. Fuel pressure or injectors. Pull a spark plug! Visual inspection!
Bad injector, bad! Lol I agree with the other posters about that dripping injector. Maybe scope the waveform on those injectors see if it looks ok and check for fuel pressure bleed off.
You proved egr is bad! But you also proved that it’s not the issue... hmmmm. Fuel pressure gauge needs to be hooked up and regulator needs to be checked. Do you have any of the old throttle bodies available? Are 5.0 and 5.7. Injectors the same? They are not. Standard part number tj4 is 5.0. Tj7 is 5.7. Would that make a difference? Is the computer looking for the 5.0 injectors but it has 5.7 injectors? Hmmmmm. I like the vehicles that are modified. Makes it interesting. Plus if you can fix it when no1 else could. It’s a good feeling! Bravo Ivan be patient and you will succeed. You are the man!!
Check fuel pressure they are picky on pressure had a few that gave me a hard time and to find out fuel pressure was about 2 psi Lower the spec thanks for the great videos
@@WECB640 good point, they are also known for TBI to intake gasket leaks! I forgot about that until you mentioned it, but it seemed to me it was always at the front where they opened up and would go lean/high idle, not rich. but there's always a first for everything :)
Ivan the o2 sensor is in the exhaust on the driversside, so swap the injectors in the thottlebody and see what 's happening. The injectors should spray a sort of misty fuel. Good luck.
I agree with others that it look like the injector might be acting up on the left side. I don't know if anyone has said this yet, but the way I used to check the spray pattern on these was to use a timing light hooked to cyl 1 and aim it at the injectors. It should be a nice cone shape spray pattern with no drips.
Blown O-ring in left injector. Check the bent throttle plate lever, base timing, and computed timing, after you replace the higher Lb per hour injectors. The best system ever, TBI is so simple, visual inspection of injectors is easy, but, not being familiar with them will send you in circles.
Good eye, James! TBI is simple in theory, but deviating from the calibration parameters can indeed throw the technician for a loop. Not too many parts to the system, but when every one has been messed with and there are no "known goods" we must be diligent to check each one thoroughly :)
@@PineHollowAutoDiagnostics in a dual injector setup, pattern is the easiest indicator - you'd have to do flow tests on each to see if you had flow mismatches -- but, i do agree with all the consensus the left injector looks like it's got family memebers working for petroleum companies.
@@PineHollowAutoDiagnostics the thing I keep going back to in the customers story is the vehicle acting up , stalling and not restarting . Secondary note: this customer seems to be a bit of a gear head and would like better performance . Holley and Fast make a pretty simple tuneable fuel injection system . It would open up options for performance for the customer .
Know i'm not the first to say this, but I don't think that right injector should be dripping @ 25.00? Hard to say exactly without eyeball it. This is a fantastic case study Ivan, a real teaser.
I'm still stuck on that Accel coil, and whatever is in the distributor for an HEI module, Ivan! :) I always forget which way weak spark, or lack of spark will push the o2's though, so I could be wrong here - certainly wouldn't be the first time whenever a computer is calling the shots! A scope on the ignition will tell the tale, I'd imagine. From the looks of the injector pattern I'd say those things are WAY to big, unless the camera refresh rate is making it look funny ... sort of like seeing a propeller spin on an airplane when filming during flight, but in reality you see right through it. These older trucks are fairly simple, so this is definitely an interesting one!! I'd be yanking my hair out here, lol - what else is new? 😂
The most important part is the ECM. The knock sensors are usually specific to the bore size. You probably already have the 350 knock sensor unless they removed the 305 one and switched it over to the 350.
This may be off the subject of fuel but I've experienced this on GM's in the past. He has number 7 and number 5 spark plug wires laying next to each other on the mount (because it looks organized). Those two firing events are the only two that fire next to each other (firing order 18536572). It ended up being a bad spark plug wire insulator and it was intermittently jumping spark to the other wire. Pure guess on my part but it was the same system I see here. This will be fun to figure out.
The left hand injector spray does look wrong - it is supposed to be a nice cone - shouldn't see drips. Check fuel regulator input & output pressures. Injector could be sticking/broken etc. Look at injector signals compared to correct ones for that engine config. You'll get it Ivan!
Those TBI's have a base idle procedure and likely would be something to cover especially if they have been replaced. They are no longer made by GM so they could be new anything or used OEM. The procedure is to unplug the idle air control electrical, key off, short pins 0 & 1 at OBD port, start engine and read RPM which should be around 650 to 750 RPM. If not, theres a leak or the idle screw needs to be accessed and turned to reach correct base idle. Once set, key off, remove jumper at OBD, connect IAC elect plug. the idle screw has a pressed in plug over it on the left side of TBI just in front of the Linkage. Some will drill it out for access. Had experienced a TBI that would never idle unless fully warmed up and trans in gear with brakes on for about 30 seconds or so. then the idle would always return to correct RPM but the cycle would start all over again once ignition was turned off and started up again, you'd have to give it 30 seconds in gear for the IAC to respond to full closed. A lower based idle RPM setting helps eliminate this concern but then the idle is too low for comfort. Should have ordered his truck with the 5.7 when he was in the market. Lots of folks simply buy whats on the lot vs. wait for a fully custom ordered vehicle.
gotta ignore the engine swap besides the headers and throttle body. The only differences in swapping a 4.3, 5.0 or 5.7 in these generation trucks was the injectors, fan shroud(if 4.3 to v8) and a chip you swap on the ecm. Everything on them was plug and play. Like you said- back to the basics!
Check the letter at the end of the EGR part number. If it's neg back pressure egr the last digit will be N for negative or P for positive. It it's a positive pressure EGR it will only open under load and will pulsate when the solenoid opens. I had to dig deep to remember that one. I used to call those injectors, "like flushing the toilet". The spray pattern is crude along side of port injectors.
Great video once again, was sooo looking forward to it. My EGR guess was incorrect. Next would be leaky injectors, that throttle body shot wasn't looking right, not really a spray, more like a drip? I would check that. My intake restriction guess also still stands: not enough air would lead to the ECM taking fuel away in an attempt to get back to stoich. At the same time it could lead to the ECM raising the idle in attempt to get more air. Just my 0.02$ :) EDIT: what I mean by restriction is an actual restriction. Some kind of blockage (my old car had a "hole" in the throttle body for air intake at idle. That hole was clogged and the car was acting like this one, both on symptoms and scan data, just an example). A leak would lead to more air being drawn and thus a LEAN condition, not a rich one.
@@PineHollowAutoDiagnostics Pine Hollow Auto Diagnostics Yes, that's how my old Opel was, it had a bypass hole for the idle and it got clogged, reporting rich at idle and stalling out. Had some mechanic replace the O2 *facepalm* and fixed it on my own eventually by unclogging the hole. Maybe something is clogged on the truck too. I would take apart the throttle body and inspect it, along with the IAC and injectors, something has to be wrong there. You'll get it fixed I'm sure, you're patient and incredibly knowledgeable, keep up the great work!
How about compression test on the O2 Sensor Side Bank (or the whole engine for that matter) Remember a speed density engine fuel strategy, has to make the assumption that the pump (engine) itself is working right, because it has no MAF. An incomplete burn from low compression will throw unburnt fuel with very little O2 into the exhaust on that side making it seem rich to the computer, and then the computer is reducing the fuel on both sides. Remember the O2 has no idea how much fuel is present just how much oxygen is present compared to outside air. Normally a misfire that burns no oxygen (ignition misfire) will cause the sensor to read more oxygen, but one from a low compression is getting a lack of O2 introduced to begin with, and then mixing the unburnt fuel into the exhaust from the other cylinders and burning what little 02 their was in the manifold. This will get worse at idle, because as RPM's come up so does the compression a bit, and the more air the pump is moving the less on bad cylinder affects the pump. Then we have to consider the lack of vacuum caused by that low compression too, that affect the manifold pressure on a speed density engine (more so at idle). I've seen more than one speed density engine with severely low compression on one cylinder act exactly this way. Great driving down the road and it won't idle right and high negative fuel trims. It's why I did the rebuild project on my 99 Grand Am 2.4 LD9 engine. If this is not the case then I would say its screwed up because the computer thinks there is a 5.0 liter pump instead of a 5.7 liter pump. (Remember we only measure 02 and not fuel). Just he same as we would expect 5G/s vs 5.7G/s on a MAF engine this size.
Check the throttle body gasket for damage.Replaced many back in the day where they break in between the two ports and most times you could open the throttle and look down and see the gasket sticking out.
Throttle body injection was popular in the 90s in Europe. It was called the single point injection (SPI), as there was almost always one injector. The ordinary style, where you have single injector for each cylinder is called multi point injection (MPI). Nowadays nobody cares about it, cause all the cars are multi or even in-cylinder injection. But back then you could often see an "MPI" sticker on the back of a car that was multi, just for everybody to see that you drive a vehicle with modern fuel system xD
when I am doing emissions test , o those gm trucks with tbi system I had had several of them failed from other shops for higher number of hc and co idle only, in one of the emission classes update for tbr license the teacher show us a trick, is this engines at idle they run rich and some times or most of the time goes in open loop , so when doing idle portion I raise up the rpm to about 900 rpm and now the 02 sensor cycles, and get in good fuel control .
i recently put a 5.7 into a 92 that had a 5.0. I changed nothing though i did have a weird idle with a fish bite and the tach would jump. Long story short, the dist had been changed with some offshore POS and it was faulty.
the EGR valve on those usually fail by rusting the bleed hole shut, then they open to far too soon and cause a tip-in low rpm major stumble/miss. right where you cruise around on the throttle, they'll go total berserk
If the computer is for a 5.o n theres now a 5.7l the volume of air going in and out are going to be greater can the o2 n computer actually accurately read correctly and compensate for that? Or is it to far out of its parameter control
You can clean the sensor ground connection but you can also take a 1.5v battery and use the small battery (+) to the sensor wire and (-) to ground and check the scanner reading for 02 voltage, if it's showing a difference you have resistance in the circuit.
I've had egr issues on my Caprice to the point where I just disabled it in the tune. Passed emissions that way, too. With a freer flowing exhaust you tend to need N type valves. But yeah I've had issues where the valve was opening when it wasn't commanded to or opening too much. Never solved that.
Long ago I have heard of this issue in this generation trucks when headers were installed. I had a 1992 GMC Sierra with the 5.0 liter engine. The stock exhaust manifold has the O2 sensor at the end of the manifold where the sensor is reading off of four firing cylinders. The O2 sensor reads the exhaust from four firing cylinders to adjust the fuel for the throttle body for all eight cylinders where on the headers the O2 sensors are tapped into only two cylinders exhaust. Two cylinders exhaust is not enough to correctly adjust the mixture for the remaining six cylinders. Friends adding headers to this generation truck reported wonky idles. The 5.0 to 5.7 swap might have amplified the problem. Would be nice of there was another port downstream on the headers where the O2 sensor could be relocated to see if reading off four cylinders this improves the issue.
A vacuum leak somewhere in the intake mainfold(s) would be something that can develop and gets worse over time by nature. The leak would be most pronounced at idle / low rpm as this is where the mixture is most sensitive to a fault. Could be a crack, bad gasket, rotten hose, leaking valve or erratic fitting of a component. ... and get that modified idle setting "bent bracket" back to where it belongs ! On the injector issue, you guys should remember that this is not a fuel injector as per regular means. It is designed to resemble the fuel flow in a standard carburettor barrel and is done so by an electric injector to make it easier and more precise to regulate the fuel injection. At low fuel levels the fuel will literally slowly drool out the injector, exactly like in a downdraught carburettor. At moderate fuel needs you would even see the injector -pulsing- at a varying rate to meter the correct amount of fuel. Only at high fuel needs you would see a constant spray inside the carburettor barrel, as the pressure to the injectopr is constant.
Think of this to if the throttle I'd part held open your tps is up so the computer is adding fuel for a throttle tip in. I'd get the idle under control then see what happens
Hello Ivan. Consider the modification of the exhaust manifolds be the main problem you have here. O2 sensors of one wire are very bad behaving on exhaust headers due to lack of heater circuit, and with headers they become cold all time and they are reporting pegged rich due to lack of sensor temperature. At that point, the ECM is pulling out fuel all time due to this, making the engine super lean and even with that the O2 sensor continues reading rich due to being cold and missreporting the real mixture on the exhaust. Solution: You should take a 3 wire oxigen sensor, typical from GM's from 1992 onwards, and modify the wiring, providing a +12v from switched ignition and direct ground to the other two wires of the sensor so the heater will become powered. This way you will have constant temperature on the O2 sensor independent on the load or throttle of the engine, giving you a correct reading on the exhaust mixture. Try this and I am sure you will get great improvements on your fuel control by the ECM. Bonus: With the OEM manifolds and the mandatory catalitic converter, single wire O2 sensors have better readings due to the heat retention of the OEM exhaust, so cooling down of the sensor is not a problem. But if you install exhaust headers and a more open exhaust system, one wire O2 sensor remains always cold and gets impossible to read properly. This is why is mandatory to install then a heated O2 sensor. I use to install the Bosch three wire sensor p/n 13077 (Rockauto) with the appropiate weatherpack wiring pigtail connector and works great for this OBD1 ECM computers, working on the 0-1v signal.
I commented on Part 1 regarding the throttle position sensor voltage possibly being out of spec, because I didn't see it directly addressed in either video. Just a thought...
There are a lot of comments about the injectors. You can check the injector spray pattern for dripping or a " skewed " pattern with a timing light. Direct the beam of the timing light onto the spray pattern. Jazz or blip the throttle and watch the enrichment. Look for an even conical spray pattern that hits the outer edges of the throttle plate as you momentarily blip the throttle. Have a great Christmas TakeCare, Bill
The OE egr's should have an N or a P stamped on them signifying negative or positive backpressure. It is very important that your replacement valve be compatible, because they look exactly the same, but function completely different.
O2 sensor I think should be back in collector to sample all cylinders or in an H pipe for the true sampling. Just my thought. Good lick with the sweet looking sounding truck. E
pretty sure those are summit racing truck headers and the O2 is right at/past where it gets the best blended flow from all 4 cylinders on that bank. if so they are CARB certified blah/blah/blah. I doubt they;d be some one off design when you can get the same headers that have been produced and still capable of passing e-check since the 90's ;)
Proberly turn out to be something stuck in the airfilter intake pipe or clogged air filter...no no no..that would incease vacuum not decrease it..forget i said that..waiting for part 3
Truck probably has a negative EGR. Also check for the vac leak around the Iac sensor. Small gasket is there Mine was trashed I made a new one And the throttle body base gasket sometimes is an issue but I never had one go bad on mine. Or start spraying carb cleaner allover the place looking for an change? I still would make sure it has the proper fuel pressure if its not at 12-13 psi these things work horribible. Maybe someone put in some aftermarket fuel pressure regulator or spring and its higher than its supposed to be over fueling at idle. or low speeds. Oh yea does this thing warm up to like 195-200 degrees at idle? Maybe they put a 180* T stat instead of a 195 that messes up everything on these. It runs too cool of course. I tried one for fun years ago and all it did was go int and out of open and closed loop when it was cold outside.
With the IAC @ 0 should not be running. air is entering somewhere opposite the bank with the 02 sensor. That gives the high idle. Also causes the lean misfire on the bank opposite the O2 senor and the rich reading on the side with the sensor.
I would be checking the regulator on the throttle body. They went out often and caused all kinds of problems. There is also a screen in the inlet line at the fitting that goes to the throttle body. That bolt that holds the lines down is a bitch to get to. Also look at the base gasket and the intake gaskets.
I wonder if the design of the intake manifold just happens to bias the fuel from the one drippy looking injector to the bank with the O2 sensor. That would match the symptoms perfectly. O2 sensor correctly reading rich, while the other bank with no feedback is trimmed excessively lean.
I would unplug brake booster hose and seal it off, and check all vacuum hoses for leaks,. also check the pcv valve, they are often overlooked, if its stuck open its like a vacuum leak.,.,
Have you performed a running compression test to see if you have a valve issue? That was my first thought when I heard the symptoms. Also I'd look at spark, they had issues back then with distributor cam gears getting worn. At a lower rpm, warmed up, there may be a little "chucking" going on causing a misfire. Once the rpm goes up there's more pressure on the gear causing it to stay in place. Might want to check that if all else fails.
I agree with the chorus of people who noticed the dripping left fuel injector. That may be THE issue. A strobe or timing light will help you see the spray fan more clearly. (The right injector looked good BTW.) Also, the EGR valve is shot. It should hold the vacuum and cause stumbling at idle. Although it's not causing the idle problem, it's never going to open because the rubber diaphragm is split. Also, the vacuum to the EGR valve should increase when throttle increases.
Can't wait for the next installment of this series, Ivan. You have the best auto mechanics channel on the Internet! (Sorry Scotty.)
Thanks Mike! You will not be disappointed....WE WILL FIX THIS TRUCK!!
I’m not sure both types of egr valves hold vacuum. I think the one design needs a little back pressure first.
Exactly right. I had no idea they made two different types before I read the service info!
Watching Ivan's thought process is amazing.
Just wait until I get frustrated haha
@@PineHollowAutoDiagnostics I'm confident you WILL figure it out !
@@PineHollowAutoDiagnostics I hear you there. I have Saturn Astra belongs to a Viet Nam vet. I am doing all the work for free. The ECM replacement install is driving me crazy. LOL Even with a TECH 2!
@@PineHollowAutoDiagnostics At least you have live data on that vehicle. All I have is flashing light codes on mine. 88 Isuzu 2.3 I-TEC. Doesn't know whether to be rich, lean or correct each time you start it. So I am setting up to make a break out box for the computer. An eight channel pico would be nice here but only have two 2ch lab scopes and three DMMs.. Going to monitor injector pulse width, O2, MAF, B+@ECM, grounds@ECM, injector modulation pulse from the distributor, engine coolant temp sensor and fuel pressure. The car has good days and bad days so I will get to see both. When I do this maybe I'll send you a picture of the total hook up just for poo and laughter as Eric would say.
Had to do this on my 1989 Mazda MPV 2.6L. The MAF was a bit skewed...fixed that one with an in-line resistor on the signal wire. Still working fine 10 years later!!!
My next check would be to see if my WIFE HAS DINNER READY YET>?.
Having so much fun reading all the comments. You have a lot of helpers on this one.
Me too!
I've only just discovered this channel - utterly brilliant in every way. Almost as compelling as Bad Obsession Motorsport.
Another thought. Oxygen sensor is only sampling one cylinder (header tube). Oem is at back of manifold and samples whole bank ......hmm
Ivan I think it's time Santa Claus brought you a exhaust gas analyzer. This is an awesome case study.
Glad you are enjoying it Dave! Definitely got a bit frustrating in the middle, but we will prevail :)
I m a fleet mechanic. I know its hard to do otherwise. When we pierce a wire, I find that in about three years that wire will oxidize at the point of fail. Not so much in the cabin, but in the engine compartment it will. I find this in our vehicles. Even when you think it stays clean. Your great to watch and Im always learning. Thanks.
"Have you ever seen injectors firing on a Throttle Body" Yes I have. Is that injector dripping fuel at 25:03 ? The fuel should be a steady stream and atomizing in the venturi.
I came here just to say the EXACT SAME THING, SHOULD BE SPRAYING NOT DRIPPING. Check fuel pump pressure & the injectors.
@@NoWr2Run The early Volvo's had that system on some of their cars.
I can tell you that is the way they worked.
They called it a single point injector on a 4 cylinder engine.on a 1.8 and 2.0 engine.
First time i have seen 2 injectors on the throttle body .
That was my thoughts too. I thought for sure Ivan was going to mention the poor spray.
True.. Dumping fuel
I agree !
Seems fuel spray on passenger injector is blurping.fuel..may have fuel pump diaphragm not holding pressure or incorrect injectors.
This case is as tough to diagnose as anything you've done on Staten island. Good luck!👍
At least I had the luxury of it being on my own lot!
Since the injectors can be unplugged separately I would try unplugging them independently and looking at idle mixture at O2 sensor as well as block and integrator. Do this for each injector. Just a thought. You and Eric O the absolute best on YT!
Would probably just stall out if you cut out half the fuel!
My thoughts exactly. I'd check for vacuum leaks as well. There are so many variables going on here. It's case where you have do the process of elimination to deal with all the variables. Diags like this can be a real pain. But when you do figure it out, it'll bring out your best. I've been through running issues similar to this in the past. I've seen sometimes it can literally take days or even weeks to figure this out. Have a merry Christmas and happy new year.
Exactly right, Paul. One variable at a time, via the path of least resistance. Takes time, patience, and lots of note-taking and trust in your diagnostic tools :)
Very interesting case!! Can’t wait for part 3!!
Hey Maic! It's an old truck, but as I realized it's not a simple diagnosis. Everything is a variable....CRAZY!
Pine Hollow Auto Diagnostics my friend, old cars are hard to fix since there are not many pids to go by. The logic of the ECM is base on few sensors! As you said too many variables! But it is fun!!
@@PineHollowAutoDiagnostics these 89s and 90s trucks drove many a man to drinking., thats why so many parts get replaced on them, because everything is somehow connected, and symptoms can be very similar. if the parts werent plentiful and cheap, these trucks would be extinct! great when running good but when they act up, you better get you a snickers.
Hey MotoYam
Excellent Test checking for the 1 wire o2 sensor. Seen that ground loss many times. GM started putting a separate ground wire soldered on the o2s for there 366 big blocks truck motors. Really enjoyed your theory. For someone who doesn't do this for a living like I do. Youved done well.👍👍
Hi Richard, thank you for the comment! I really thought I was on to something, but that ground was near perfect! Oh well, that just makes it more interesting ;)
Now to dig into the fuel system & come up with the best solution, nice work Ivan!
Ivan. I have had the same exact problem with my 1992 c1500. When I bought it the engine was bad. Mine was originally a 305 and that’s what I replaced it with. Now I got a used engine. The standings on the block were that of a TBI 305. I later found out that the cylinder heads were 081 heads and from my research were likely from a TPI engine. Now I also noticed my overall engine vacuum was lower than it should be. I checked all external leaks, none found. I tried a different intake manifold I had with the same results. Doing some more tease arch I found the base timing for the TPI engine was 7*BTDC, not the 0* of the TBI set up. Now I mentioned the low vacuum I was measuring it at 15” of mercury. Once I advanced the timing to 7* it brought the vacuum up to 20”. There was also another difference between the two cylinder head setups. That was the heat range of the spark plugs. I changed to the hotter plugs of the TPI head and between the two changes my idle issue when warm in closed loop idle was much better. My block learn values went from 102-103 to about 120 or so. Though this information may not solve this trucks problems it did for mine. Please also note that I did every check you have done so far. Additionally I did try a different computer and a different prom. Something you may want to look at prom related is a tab for driveway stall out on these trucks which was supposed to be solved with an updated prom. If this helps great. If not I hope you find this trucks problem. As always great videos and I look forward to hopefully many more!
Thanks for the info, David! It's crazy how many hidden variables there are on these "old school" TBI systems! Had no idea what I was getting into with this truck haha
@@PineHollowAutoDiagnostics I mentioned this in the first video; i find it odd that your vacuum is so low - verify the map sensor compared to manifold pressure at idle.
n3lee Yes good suggestion. I did when I was diagnosing my trucks problem. I am lucky enough to have another TBI truck that runs awesome so in addition to comparing the pids for the map sensors with the engines at the same operating temperatures I was able to swap in the “know good” sensor to the truck that was not running well and the results were the same. Low vacuum at hot idle.
if you put a timing light behind the throttle body pointed at the injectors you can see the patterns pretty good. Nice series Ivan thanks for your time.. Merry Christmas
Man, this one's got me scratching my head! There's nothing like a good Christmas mystery though! Kudos to your thought processes, Ivan. I can almost see the wheels in your brain working. I too was noticing the spray pattern coming out of that one injector. I can't wait for the next installment to see if it's related! Get this one fixed, and the borscht and vodka's on me!
Glad you are enjoying watching me struggle haha! It gets more frustrating before the final victory :)
You can check injector spray pattern with your timing light(while you are checking ignition timing),point the light at each injector and it will freeze pattern. Should be no drips.Check prom and calpack numbers that are on each against list for proper application in old G.M. parts catalog.
Oh boy, looking rich! Looking forward to P3!
It's been so long since I've seen/had one of these, my head is already swimming.
You ARE right though... Keep returning to the basics.
Like going from tubes to solid state, the principles remain the same. Only the checks and balances become tighter...
I can't get this thought out of my head:
The Chevy 305, 327, and 350 were the SAME ENGINE! Stoke and bore were the only difference. A minor difference in carb jetting, but EVERYTHING else was the same...
Test preasure regulator! ! Great videos. Thank you.
You know you have to get some waveforms on those dual peak injectors while you have them together with a PICO! I've been hoping to run across some with my Hantek for a while now.
Ivan interesting study. I watched the first video. AND now this one. I would call it too high psi on the fuel pump as it's not designed for this type of engine. But maybe bad injector. Will wait to see part 3. :) can't walt lol
Great thought, Josh! Hint: there is more than one problem, and the effect is compounded ;0
Ivan, I have no idea where to go next but that is one sweet truck. I hope you are able to get her fixed up.
He'll get it, and it'll spin heads at it's simplicity. Going from a 305, to a 350 was an extremely minor change back in those days.
The fact that it was changed MAY be the cause of confusion.
Pretend is is ALL original and go from there. These dinasours were NOT as complicated as multi port...etc.
Pretend it still runs on a carb!
When you stopped and went back to diagnose it again acting as if you had no prior knowledge was stunning. It's what we all need to remember about problems, I know that when thinking about cars or any problems I get caught in a loop then throw the parts cannon at it: be cars or life.
I have watched a couple thousand RUclips videos dealing with cars too mowers and that idea to back up has never been said. Sensory overload. Thanks that's another tool for me to remember.
Yeah sensory overload for sure! My mind often gets carried away with all the info and possibilities. One of the hardest parts of problem solving is keeping the thoughts organized, and designing very specific experiments to have a clear answer to every fork in the road. Might take some time, but in most cases it gets to the answer more efficiently and accurately :)
This may seem a little far fetched but check the ignition module. I have had quite a few that had similar symptoms. It relies on a signal from the distributor to generate a fuel pulse. You have covered about Everything else. Helps if you had a spare distributor assembly to give it a shot. There is a tan and black striped wire under the dash to unplug. Set initial ignition timing to 0 degrees no more no less. Plug said wire back in. Just had a lot of experience with these trucks lol. Some models said wire was under the hood by the heater core under a plastic cover where the fuel pump relay lives. Hope this helps!
Excellent suggestion Chris!
ohh, plug location, I said under the hood near heater box on passenger side, but now I recall some being inside like you said :))
memory lane lol
not sure when he replaced the injectors if he point new ones in at time of engine swap looks like one side is duping more like its not performing well … I would check fuel flow and also fuel pressure ,, yep my next step would be fuel delivery and pressure ...great content and its fun to watch your diagnostics steps,, great job
If the base idle could not be controlled without messing with screws then suspect a bad throttle body gasket. Especially if iac counts are pegged low.More air equals more fuel.
This is like the car that just keeps on giving and giving boom lol next part now
Ivan, you write like a medical doctor writing a prescription. :-)
loving this as i drive a 94 silverado 5.7 tbi .... i have headers with long tube the o2 is in the collector on left bank ..no problems .. ive been lead to believe that compression and cam can also cause running problems .. is it a tbi engine thats in the truck ... generic crate motor is not compatable ... just another line of thought ... lots of great comments here ... and a lot of interest for good ole truck ... was the last tbi truck ivan fixed for the rev it guy at the scrap yard .... is the map vac line on the right fitting one is a breather ..also check for tbi mods jb weld ect gadjet man groove ..looking forward to part 3 ..
I understand your frustrations my friend.i have seen on some old small block Chevy's were intake manifold gaskets have simtoms similar to what u are experiencing.and it's always when engine comes up to warmer temperature when this occurred.its a possibility.guess smoking it out when it's nice n warm might Chase t problem out.i have also seen t base of the throttle body draw vacuum were t butterfly plates join at the throttle rod.
This is a tricky one Ivan. You’re the best man solve it.
Just getting warmed up haha
Pine Hollow Auto Diagnostics will look forward to the third instalment 👍🏻
Throttle Body Gasket at back is notorious for blowing out a small section. Will elevate idle from a little to 1200 rpm. Of course Map senses it. Also check thermal air door in air filter housing snout. Supposed to open from exhaust temp but foil tube always gets chunked. Also don’t overlook base timing. Usually sets at zero plus/minus couple degrees.
Gotta love them old OBD1 GM vehicles...(pre 1995/95) they were one of the rare ones to give out a datastream. I still have an old Snap-On MTG2500 scanner I use for the old stuff...always comes in clutch for an oddball issue on an older GM!
Aaah the old red brick! Funny that you mention it...might make an appearance later in this saga ;)
@@PineHollowAutoDiagnostics I love my old brick! I've got al lthe adapters for all the hot mess back then for Chrysler, Jeep, Ford, Toyota, Nissan and whatnot for American and Japanese vehicles...shop has a newer Solus series scanner for OBD2 stuff...but the older stuff...out comes the 2500 and lemme tell ya, I'm not gettin rid of it any time soon! Too handy...way too handy.
Dash display had grounding issues, was an issue with that generation. Ask me how I know. Failed intake gaskets are common on these engines as well. Fuel pressure or injectors. Pull a spark plug! Visual inspection!
Bad injector, bad! Lol I agree with the other posters about that dripping injector. Maybe scope the waveform on those injectors see if it looks ok and check for fuel pressure bleed off.
You proved egr is bad! But you also proved that it’s not the issue... hmmmm. Fuel pressure gauge needs to be hooked up and regulator needs to be checked. Do you have any of the old throttle bodies available? Are 5.0 and 5.7. Injectors the same? They are not. Standard part number tj4 is 5.0. Tj7 is 5.7. Would that make a difference? Is the computer looking for the 5.0 injectors but it has 5.7 injectors? Hmmmmm. I like the vehicles that are modified. Makes it interesting. Plus if you can fix it when no1 else could. It’s a good feeling! Bravo Ivan be patient and you will succeed. You are the man!!
Thanks for the kind words, Bill! This was definitely a crash course on GM TBI for me. You're definitely on the right track with those questions :)
Check fuel pressure they are picky on pressure had a few that gave me a hard time and to find out fuel pressure was about 2 psi Lower the spec thanks for the great videos
Hmmm, but this thing is running rich, which would point to high fuel PSI? Don't worry we'll get to the Fuel Delivery system very soon :)
@@WECB640 good point, they are also known for TBI to intake gasket leaks! I forgot about that until you mentioned it, but it seemed to me it was always at the front where they opened up and would go lean/high idle, not rich. but there's always a first for everything :)
Ivan the o2 sensor is in the exhaust on the driversside, so swap the injectors in the thottlebody and see what 's happening. The injectors should spray a sort of misty fuel. Good luck.
I have seen the brake booster with a vacuum leak . Good luck.
it would go high idle and be lean, trying to richen the mixture. opposite is happening there.
I agree with others that it look like the injector might be acting up on the left side. I don't know if anyone has said this yet, but the way I used to check the spray pattern on these was to use a timing light hooked to cyl 1 and aim it at the injectors. It should be a nice cone shape spray pattern with no drips.
Blown O-ring in left injector.
Check the bent throttle plate lever, base timing, and computed timing, after you replace the higher Lb per hour injectors.
The best system ever, TBI is so simple, visual inspection of injectors is easy, but, not being familiar with them will send you in circles.
Good eye, James! TBI is simple in theory, but deviating from the calibration parameters can indeed throw the technician for a loop. Not too many parts to the system, but when every one has been messed with and there are no "known goods" we must be diligent to check each one thoroughly :)
@@PineHollowAutoDiagnostics in a dual injector setup, pattern is the easiest indicator - you'd have to do flow tests on each to see if you had flow mismatches -- but, i do agree with all the consensus the left injector looks like it's got family memebers working for petroleum companies.
@@PineHollowAutoDiagnostics the thing I keep going back to in the customers story is the vehicle acting up , stalling and not restarting . Secondary note: this customer seems to be a bit of a gear head and would like better performance . Holley and Fast make a pretty simple tuneable fuel injection system . It would open up options for performance for the customer .
Alrght!.... a trilogy! Can't wait for 'Rise of Ivan'.
We got plenty of time before Christmas Day ;D
Know i'm not the first to say this, but I don't think that right injector should be dripping @ 25.00? Hard to say exactly without eyeball it. This is a fantastic case study Ivan, a real teaser.
Actually look normal to me, from what I remember of those
I'm still stuck on that Accel coil, and whatever is in the distributor for an HEI module, Ivan! :) I always forget which way weak spark, or lack of spark will push the o2's though, so I could be wrong here - certainly wouldn't be the first time whenever a computer is calling the shots! A scope on the ignition will tell the tale, I'd imagine. From the looks of the injector pattern I'd say those things are WAY to big, unless the camera refresh rate is making it look funny ... sort of like seeing a propeller spin on an airplane when filming during flight, but in reality you see right through it.
These older trucks are fairly simple, so this is definitely an interesting one!! I'd be yanking my hair out here, lol - what else is new? 😂
I'll be yanking my hair out very soon I promise haha
@@PineHollowAutoDiagnostics - 😂🤣😂 Definitely a tough one there!
Need the knock sensor, ecm (or prom chip), and electronic spark control module from the 5.7.
ding ding ding , we have a winner . That new engine didnt come with an EGR valve and the new Ecm cant read or adjust the EGR valve
Ding , Ding , Ding , We have a Winner
If there is no vibrations or dentonations to ping the knock sensor is useless. How would that affect anything?
The most important part is the ECM. The knock sensors are usually specific to the bore size. You probably already have the 350 knock sensor unless they removed the 305 one and switched it over to the 350.
@@weldingjunkie it would limit the timing advance, but not cause a miss at idle. it would be like umplugging the timing connector
You can get a really good look at injector spray patterns using an adjustable timing light. They will appear like still shots
This may be off the subject of fuel but I've experienced this on GM's in the past. He has number 7 and number 5 spark plug wires laying next to each other on the mount (because it looks organized). Those two firing events are the only two that fire next to each other (firing order 18536572). It ended up being a bad spark plug wire insulator and it was intermittently jumping spark to the other wire. Pure guess on my part but it was the same system I see here. This will be fun to figure out.
WOW now that is a crazy scenario, Wyatt!! Never would have thought that would be possible!
The left hand injector spray does look wrong - it is supposed to be a nice cone - shouldn't see drips. Check fuel regulator input & output pressures. Injector could be sticking/broken etc. Look at injector signals compared to correct ones for that engine config. You'll get it Ivan!
Those TBI's have a base idle procedure and likely would be something to cover especially if they have been replaced. They are no longer made by GM so they could be new anything or used OEM. The procedure is to unplug the idle air control electrical, key off, short pins 0 & 1 at OBD port, start engine and read RPM which should be around 650 to 750 RPM. If not, theres a leak or the idle screw needs to be accessed and turned to reach correct base idle. Once set, key off, remove jumper at OBD, connect IAC elect plug. the idle screw has a pressed in plug over it on the left side of TBI just in front of the Linkage. Some will drill it out for access. Had experienced a TBI that would never idle unless fully warmed up and trans in gear with brakes on for about 30 seconds or so. then the idle would always return to correct RPM but the cycle would start all over again once ignition was turned off and started up again, you'd have to give it 30 seconds in gear for the IAC to respond to full closed. A lower based idle RPM setting helps eliminate this concern but then the idle is too low for comfort.
Should have ordered his truck with the 5.7 when he was in the market. Lots of folks simply buy whats on the lot vs. wait for a fully custom ordered vehicle.
gotta ignore the engine swap besides the headers and throttle body. The only differences in swapping a 4.3, 5.0 or 5.7 in these generation trucks was the injectors, fan shroud(if 4.3 to v8) and a chip you swap on the ecm. Everything on them was plug and play. Like you said- back to the basics!
Check the letter at the end of the EGR part number. If it's neg back pressure egr the last digit will be N for negative or P for positive. It it's a positive pressure EGR it will only open under load and will pulsate when the solenoid opens. I had to dig deep to remember that one. I used to call those injectors, "like flushing the toilet". The spray pattern is crude along side of port injectors.
Great video once again, was sooo looking forward to it. My EGR guess was incorrect. Next would be leaky injectors, that throttle body shot wasn't looking right, not really a spray, more like a drip? I would check that. My intake restriction guess also still stands: not enough air would lead to the ECM taking fuel away in an attempt to get back to stoich. At the same time it could lead to the ECM raising the idle in attempt to get more air. Just my 0.02$ :)
EDIT: what I mean by restriction is an actual restriction. Some kind of blockage (my old car had a "hole" in the throttle body for air intake at idle. That hole was clogged and the car was acting like this one, both on symptoms and scan data, just an example). A leak would lead to more air being drawn and thus a LEAN condition, not a rich one.
Interesting hypotheses. Like an air bypass hole for idle? This thing just has a throttle stop screw, and the IAC to meter the air at idle...
@@PineHollowAutoDiagnostics Pine Hollow Auto Diagnostics Yes, that's how my old Opel was, it had a bypass hole for the idle and it got clogged, reporting rich at idle and stalling out. Had some mechanic replace the O2 *facepalm* and fixed it on my own eventually by unclogging the hole. Maybe something is clogged on the truck too. I would take apart the throttle body and inspect it, along with the IAC and injectors, something has to be wrong there. You'll get it fixed I'm sure, you're patient and incredibly knowledgeable, keep up the great work!
Anyone remember the days when trucks were trucks and Chevy was a bow-tie?
How about compression test on the O2 Sensor Side Bank (or the whole engine for that matter) Remember a speed density engine fuel strategy, has to make the assumption that the pump (engine) itself is working right, because it has no MAF. An incomplete burn from low compression will throw unburnt fuel with very little O2 into the exhaust on that side making it seem rich to the computer, and then the computer is reducing the fuel on both sides.
Remember the O2 has no idea how much fuel is present just how much oxygen is present compared to outside air. Normally a misfire that burns no oxygen (ignition misfire) will cause the sensor to read more oxygen, but one from a low compression is getting a lack of O2 introduced to begin with, and then mixing the unburnt fuel into the exhaust from the other cylinders and burning what little 02 their was in the manifold. This will get worse at idle, because as RPM's come up so does the compression a bit, and the more air the pump is moving the less on bad cylinder affects the pump.
Then we have to consider the lack of vacuum caused by that low compression too, that affect the manifold pressure on a speed density engine (more so at idle). I've seen more than one speed density engine with severely low compression on one cylinder act exactly this way. Great driving down the road and it won't idle right and high negative fuel trims. It's why I did the rebuild project on my 99 Grand Am 2.4 LD9 engine.
If this is not the case then I would say its screwed up because the computer thinks there is a 5.0 liter pump instead of a 5.7 liter pump. (Remember we only measure 02 and not fuel). Just he same as we would expect 5G/s vs 5.7G/s on a MAF engine this size.
Excellent analysis. We will touch on all aspects, including engine mechanical, and the computer mismatch :)
Check the throttle body gasket for damage.Replaced many back in the day where they break in between the two ports and most times you could open the throttle and look down and see the gasket sticking out.
Throttle body injection was popular in the 90s in Europe. It was called the single point injection (SPI), as there was almost always one injector. The ordinary style, where you have single injector for each cylinder is called multi point injection (MPI). Nowadays nobody cares about it, cause all the cars are multi or even in-cylinder injection. But back then you could often see an "MPI" sticker on the back of a car that was multi, just for everybody to see that you drive a vehicle with modern fuel system xD
when I am doing emissions test , o those gm trucks with tbi system I had had several of them failed from other shops for higher number of hc and co idle only, in one of the emission classes update for tbr license the teacher show us a trick, is this engines at idle they run rich and some times or most of the time goes in open loop , so when doing idle portion I raise up the rpm to about 900 rpm and now the 02 sensor cycles, and get in good fuel control .
One of our awesome drain plugs will fix it right up.
i recently put a 5.7 into a 92 that had a 5.0. I changed nothing though i did have a weird idle with a fish bite and the tach would jump. Long story short, the dist had been changed with some offshore POS and it was faulty.
the EGR valve on those usually fail by rusting the bleed hole shut, then they open to far too soon and cause a tip-in low rpm major stumble/miss.
right where you cruise around on the throttle, they'll go total berserk
You should have titled this, "A very Chevy Xmas!"
If the computer is for a 5.o n theres now a 5.7l the volume of air going in and out are going to be greater can the o2 n computer actually accurately read correctly and compensate for that? Or is it to far out of its parameter control
The distributor pickup magnet can change base timing as temps change pull timing connector check timing through entire warm up
I've seen the timing suddenly jump 30 degrees on old pickup magnets rivet type
You can clean the sensor ground connection but you can also take a 1.5v battery and use the small battery (+) to the sensor wire and (-) to ground and check the scanner reading for 02 voltage, if it's showing a difference you have resistance in the circuit.
This would be faster than your check here. (quick tip).
I've had egr issues on my Caprice to the point where I just disabled it in the tune. Passed emissions that way, too. With a freer flowing exhaust you tend to need N type valves. But yeah I've had issues where the valve was opening when it wasn't commanded to or opening too much. Never solved that.
Long ago I have heard of this issue in this generation trucks when headers were installed. I had a 1992 GMC Sierra with the 5.0 liter engine. The stock exhaust manifold has the O2 sensor at the end of the manifold where the sensor is reading off of four firing cylinders. The O2 sensor reads the exhaust from four firing cylinders to adjust the fuel for the throttle body for all eight cylinders where on the headers the O2 sensors are tapped into only two cylinders exhaust. Two cylinders exhaust is not enough to correctly adjust the mixture for the remaining six cylinders. Friends adding headers to this generation truck reported wonky idles. The 5.0 to 5.7 swap might have amplified the problem. Would be nice of there was another port downstream on the headers where the O2 sensor could be relocated to see if reading off four cylinders this improves the issue.
A vacuum leak somewhere in the intake mainfold(s) would be something that can develop and gets worse over time by nature.
The leak would be most pronounced at idle / low rpm as this is where the mixture is most sensitive to a fault.
Could be a crack, bad gasket, rotten hose, leaking valve or erratic fitting of a component.
... and get that modified idle setting "bent bracket" back to where it belongs !
On the injector issue, you guys should remember that this is not a fuel injector as per regular means. It is designed to resemble the fuel flow in a standard carburettor barrel and is done so by an electric injector to make it easier and more precise to regulate the fuel injection.
At low fuel levels the fuel will literally slowly drool out the injector, exactly like in a downdraught carburettor.
At moderate fuel needs you would even see the injector -pulsing- at a varying rate to meter the correct amount of fuel.
Only at high fuel needs you would see a constant spray inside the carburettor barrel, as the pressure to the injectopr is constant.
Think of this to if the throttle I'd part held open your tps is up so the computer is adding fuel for a throttle tip in. I'd get the idle under control then see what happens
yeah, him saying they "bent" something is probably the throttle plate stop arm, instead of removing the plug and adjusting the stop screw
Hello Ivan.
Consider the modification of the exhaust manifolds be the main problem you have here. O2 sensors of one wire are very bad behaving on exhaust headers due to lack of heater circuit, and with headers they become cold all time and they are reporting pegged rich due to lack of sensor temperature.
At that point, the ECM is pulling out fuel all time due to this, making the engine super lean and even with that the O2 sensor continues reading rich due to being cold and missreporting the real mixture on the exhaust.
Solution:
You should take a 3 wire oxigen sensor, typical from GM's from 1992 onwards, and modify the wiring, providing a +12v from switched ignition and direct ground to the other two wires of the sensor so the heater will become powered.
This way you will have constant temperature on the O2 sensor independent on the load or throttle of the engine, giving you a correct reading on the exhaust mixture.
Try this and I am sure you will get great improvements on your fuel control by the ECM.
Bonus: With the OEM manifolds and the mandatory catalitic converter, single wire O2 sensors have better readings due to the heat retention of the OEM exhaust, so cooling down of the sensor is not a problem. But if you install exhaust headers and a more open exhaust system, one wire O2 sensor remains always cold and gets impossible to read properly.
This is why is mandatory to install then a heated O2 sensor.
I use to install the Bosch three wire sensor p/n 13077 (Rockauto) with the appropiate weatherpack wiring pigtail connector and works great for this OBD1 ECM computers, working on the 0-1v signal.
Excellent info, thank you! I like the heat retention explanation.
Check ground at thermostat housing
I commented on Part 1 regarding the throttle position sensor voltage possibly being out of spec, because I didn't see it directly addressed in either video. Just a thought...
There are a lot of comments about the injectors.
You can check the injector spray pattern for dripping or a " skewed " pattern with a timing light. Direct the beam of the timing light onto the spray pattern. Jazz or blip the throttle and watch the enrichment. Look for an even conical spray pattern that hits the outer edges of the throttle plate as you momentarily blip the throttle.
Have a great Christmas
TakeCare,
Bill
Cool tip! Thanks Bill, you too!
The OE egr's should have an N or a P stamped on them signifying negative or positive backpressure. It is very important that your replacement valve be compatible, because they look exactly the same, but function completely different.
I actually read that in service info! Had no idea they had two different designs lol
O2 sensor I think should be back in collector to sample all cylinders or in an H pipe for the true sampling. Just my thought. Good lick with the sweet looking sounding truck.
E
pretty sure those are summit racing truck headers and the O2 is right at/past where it gets the best blended flow from all 4 cylinders on that bank.
if so they are CARB certified blah/blah/blah. I doubt they;d be some one off design when you can get the same headers that have been produced and still capable of passing e-check since the 90's ;)
All those new parts makes me think "just because they're new, doesn't mean they're good."
Precisely. We will find some "bad NEW parts" very soon ;)
Proberly turn out to be something stuck in the airfilter intake pipe or clogged air filter...no no no..that would incease vacuum not decrease it..forget i said that..waiting for part 3
Truck probably has a negative EGR. Also check for the vac leak around the Iac sensor. Small gasket is there Mine was trashed I made a new one And the throttle body base gasket sometimes is an issue but I never had one go bad on mine. Or start spraying carb cleaner allover the place looking for an change? I still would make sure it has the proper fuel pressure if its not at 12-13 psi these things work horribible. Maybe someone put in some aftermarket fuel pressure regulator or spring and its higher than its supposed to be over fueling at idle. or low speeds. Oh yea does this thing warm up to like 195-200 degrees at idle? Maybe they put a 180* T stat instead of a 195 that messes up everything on these. It runs too cool of course. I tried one for fun years ago and all it did was go int and out of open and closed loop when it was cold outside.
With the IAC @ 0 should not be running. air is entering somewhere opposite the bank with the 02 sensor. That gives the high idle. Also causes the lean misfire on the bank opposite the O2 senor and the rich reading on the side with the sensor.
Счастливого Рождества тебе и твоей семье Иван !
Spasibo! :)
Apply a stronger vacuum to the map sensor with the vacuum pump to see if your fuel trim comes down.
I would be checking the regulator on the throttle body. They went out often and caused all kinds of problems. There is also a screen in the inlet line at the fitting that goes to the throttle body. That bolt that holds the lines down is a bitch to get to. Also look at the base gasket and the intake gaskets.
I wonder if the design of the intake manifold just happens to bias the fuel from the one drippy looking injector to the bank with the O2 sensor. That would match the symptoms perfectly. O2 sensor correctly reading rich, while the other bank with no feedback is trimmed excessively lean.
I would unplug brake booster hose and seal it off, and check all vacuum hoses for leaks,. also check the pcv valve, they are often overlooked, if its stuck open its like a vacuum leak.,.,
great trucks, but very tricky sometimes to diagnose, any truck vacuum controlled with primitive obd 1 can drive you crazy,
There is an air bleed valve screw in that throttle body, it is likley too open
May need a heated O2 with headers. Just not enough heat compared to manifolds. I think the AC Delco AFS-74 is a good upgrade.
Check Fuel Pressure. Also, Pass side injector is not atomizing fuel, maybe it is cracked or plugged.
Are the ems the same for the 5.0 and 5.7 ? That could be the problem
That map sensor like you said
Are the injectors firing equal amounts of fuel The one on the left looks like it owns shares in Exxon.
spoke too soon, saw you doing that!
Wow, an underhood lamp. Don't see them anymore.
Have you performed a running compression test to see if you have a valve issue? That was my first thought when I heard the symptoms. Also I'd look at spark, they had issues back then with distributor cam gears getting worn. At a lower rpm, warmed up, there may be a little "chucking" going on causing a misfire. Once the rpm goes up there's more pressure on the gear causing it to stay in place. Might want to check that if all else fails.
Brand new distributor, but with this truck, EVERYTHING is on the table!
Is the engine a factory stock 5.7? Which engine is the new ECM and throttle body for?
is the intake the cross h design or a plenum runner design. a cross h design with the 02 where its at would make for a real finicky fuel system
Fuel pressure regulator
shower MAP sensor membrane with some brake cleaner:)