How to test for a restricted exhaust (catalytic converter)
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- Опубликовано: 5 окт 2024
- 2003 Impala 3400 V-6.
How to perform an exhaust back-pressure test.
Symptoms:
very low power (could not accelerate past 30 mph)
pinging and detonation
Fix:
replace the restricted catalytic converter
Testing methods shown:
O2 sensor reading at wide open throttle (shows fuel delivery and direction for our low power complaint)
exhaust backpressure test using a gauge installed in the upstream O2 port
Tools used:
Snap-on Solus Pro
exhaust back-pressure gauge
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Playlist:
(Chapter 1) Misfire ID, Compression Test, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DVOM
• (Chapter 1) Misfire ID...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
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Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.
12 years later and this video is still relevant. Amazing in mastering the fundamentals
I've never been so captivated by a single users videos before. This is outstanding! Where did you go to school at? Like I commented on another vid, your knowledge on SO MANY different systems, the test procedures, and CORRECT way to diagnose so many common problems is amazing. Kudos to you sir. You make what we both know is difficult, look incredibly easy.
This video is perfect, short/sweat and to the point.
I think you mean sweet. Sweat is perspiration.
Wow i learned much more than diagnosing a clogging converter. TY for showing the scanner tool and all the values!
here in the uk i work for vauxhall as a tech,that high pitched whistle could be the blocked cat or even the rocker cover baffle & sometimes the intake manifold itself!very informative video mann!
Just solved a problem thats had me in circles thank you
Ditto
had an 02 s10 last week same gauge you used pegged the gauge out at 2500 rpm! used your procedure as shown. except minus getting flipped off by people for holding traffic up...
Love the comments/pop-ups on the screen. Adding notes to my Engine perf. diag. book as I go. Love this channel!!!
Thank you!
Paul, very nice to test to get the right direction of diagnosis that is very important. I like when you prove your test not only one way but with two different ways. Looks like there are lots of cars going to fixed by me soon as I used to send them away. I don't see one video of yours that is not important to me. I am just scared, if I could accidently miss one to watch. I am alsot trying organize myself so that I wouldn't miss any.
Keep watching and keep learning thanks teacher
It pays to read other peoples comments in other videos because if I hadn't done just that while researching a P0420 code I wouldn't have read someones suggestion to get a free exhaust back-pressure check at Midas. This led me to ask YT for exhaust back-pressure test and thankfully I wound up here. Thanks very very very much for this 101 video and thanks for RUclips for making it possible to post this valuable information. And I mean it sincerely!
This video is straight-up brilliant
Great video and diag. Love when techs know there stuff
@buddiiee The restrictions in an exhaust system come from a melted and broken apart catalyst. The pieces of the cat can become trapped in the muffler too so at times the exhaust must be replaced from the cat. all the way back to the muffler. (including the cat. too of course).
After the repairs the system should also be checked for a cause of the cat. failure. Its never good to just replace the cat. without checking for a cause.
Thanks for this how to just diagnosed my 2004 malibu clogged cat!
Actually being you said that, your right there was no return line coming from it.. Well I'll see where I get tomorrow, Thanks again for your input and help man. I figured who else to go to with a confusing driveability issue than you. Have a good night!
Thats good enough, just wanted to make sure it wasn't dead before we continue. For your fuel pressure test (since it is the regulated type), disconnect the vac, hose and perform a WOT snap, pressure should not drop off during the test.
As I just typed this....the regulator you mentioned may not be a regulator, it could be a pulsator with a vacuum hose on it. Which would make this a mechanical returnless system. They look like regulators. see if there is a return line on the rail
master of knowledge
Again thank you for your fast response. Actually yes, 98 Ford Taurus, 3.0 OHV engine, vacuum regulated fuel system. Fuel pressure was a little below spec. about 30 psi, but ran okay. (originally a no start and towed in) Both oxygen sensors switched good, but during WOT test, bank 2 went lean, although managed to run good. I did scope the fuel pump current which was around 4.5 amps but the waveform had a few spikes in it. Ran into the car at the end of the day so thats about all the info for now.
Other test methods:
1. use vacuum gauge (0,65 bar): § WOT : zero vacuum.
§ If restricted: 2000 RPM -> vacuum drops more and more
2. infrared thermometer test on cat (@ 2000 RPM, outlet 60° hotter than inlet)
3. scantool: 2nd O2-sensor steady voltage (±0,5V)
I dont understand. Theres not supposed to be vacuum at 2000 rpm and by vacuum drop do you mean pressure goes up or down?
Great tips , thanks !
Very helpful thank u for such a clear speaking to the point video
Thank you very much for the positive feedback on the book. As far as a download, there isn't one however you can print from it and make your own paper version. Of course your access never expires either.
@westin1985 the intent of this video is not about performance tuning it is simply how to recognize if your cat. is restricted. backpsi at idle should be zero. in fact backpsi under 3000 rpm in PARK (meaning no load) should be very near zero. reason being is in park there is not much throttle opening so the engine isn't breathing very much
@altlandf Not for a short test drive and I have done that before to test for a plugged exhaust.
Your OBDII code reader should have some data PIDS you can look at, so if it does, then yes fuel trim can be seen with it. You are not using fuel trim to ID a plugged exhaust.
Yes you can use a regular psi gauge, in fact I made my own adapter with an old O2 sensor and I use my cheep vacuum /psi gauge
thanks man! I really appreciate the support.
Love it, great troubleshooting process!
Love the vid. Our 13 expedition 5.4 3v. had a clogged cat. Dealer wanted to do all the work backwards. Tune up. Injectors. Ignition coils. Etc (out of warranty)$1400 before replacing the cat. (Still under warranty)
After several meetings with mechanic and his stupidvisor, I them if they can find a problem after the cat was replaced then I will have it repaired. Finally got warranty cat replaced, and magically the car ran perfect. They couldn't find anything wrong.
Wish I knew what caused it.
I have also bought this amazing book, the little that I translated into Spanish is excellent.
also published in Spanish
saludos desde LIMA - PERU
I bought your book. I like it. Very good information.
Old, but still accurate. I just did a pressure test and the needle went half way on start up and when I pressed the pedal it pegged it immediately.
Robinson auto has a similar video regarding a bad cat due to a bad plug wire causing misfire, customer was driving for a while with the engine light on-- the plug wire was arcing on the engine, one thing causes a chain reaction
Mr. Danner, I have one for you. 03 ram 2500 5.7 Hemi. P0300. I just got my Launch X-431 V and I only barely know how to use it but the little bit I do know I'm questioning because the cat has been cut out and a pipe put in it's place. It's been that way for years so I know that's not the problem here but I don't know how o2 and fuel trim data will look. I had access to a ton of parts off a known good engine so I threw EVERYTHING at it, injectors with rail, plugs, wires, coils...needless to say...same issue. Not only is it a p0300 but it's got a flashing check engine light. The live misfire data shows most of the misfires on 2 and 3, opposite sides of the engine! I've been watching your videos and am starting to learn what a normal reading of short and long term fuel trim, o2 but now this thing has no cat. What happens to the downstream o2 sensor data....same as if it did have a cat? I'm jut guessing here but it seems like it would read exactly the same as the upstream o2 sensor. I put a vacuum gage on her and it actually reads in the "normal range" of the gage but it's very close to the "timing too late" or something to that effect. It's been a plow truck and race car hauler all it's life...maybe this is showing me I have my chain is too stretched and it's throwing random multiple misfire codes? I honestly barely know what to do with the scanner so any help you can offer would be greatly appreciated.
Thanks in advance.
@spelunkerd Not sure about the alcohol content, but after a repair, I make sure fuel trim #s look normal under different loads, also that there is no misfire. Truthfully on the Impala and Monte Carlo, I have seen so many melted cats. and found no cause when I am done. I think it may be in the programming of the fuel curve?. Here in the aftermarket, we just put a new cat in it (factory cat of course) and if everything looks good we let it go.
Nice diagnostic walk through.
Thank you so much!
My reason for suspecting the catalytic converter... is I recently cleaned all the carbon off the intake manifold and throttle body. Most was wiped away, but obviously some went through the engine.
I also used to have problems pulling grades when I bought the used truck. But it was 50-90% fixed when I replaced the plugs & cleaned the TB/MAFS/Intake. Putting my hand to the exhaust is sad. It's like a very light wind.
cool man, I look forward to meeting you.
thats awesome Richard! How did you find us and what helped you make this decision to come here?
THANK YOU VERY MUCH FOR ALL THIS GREAT INFORMATION, GOD BLESS.
What is the normal reading for the exhaust back pressure should be ?
yep. just make sure there are no 02 codes and exhaust leaks
Going to test my car with this very same method. Hopefully both of my cats are not clogged. But this is great start to not throw way a $1k in a pair of cats of not needed.
Another great class Paul, always waiting for your videos to keep learning from your book, thank you..
Thank you my friend!
It certainly wouldn't be from a dirty MAF or fuel pressure problem as this would effect both banks. Do you have a car/truck that is doing that? Rich on one bank, and lean on the other at WOT?
Double check that WOT O2 test for me. If you can, limit your data PIDs to just the two upstream O2s. This will allow for much faster data updates. Let me know the result
That is strange, not sure I've seen that before. Lets not totally rule out fuel pressure here yet. Maybe it is borderline. Or maybe the MAF is dirty. Check MAF volts, it should go over 4v at WOT redline. Also check your fuel pressure on a WOT snap too. actually I think you can monitor fuel pressure on scan data on that system right. If so pull that PID up during your test drive too.
Last question, are you sure the bank that is dropping lean has a functional O2 in it?
I didn't look at fuel trim closely for this one, but I know at idle and low speed they were in the normal range. Well at least normal enough for me to not look to closely. Also at WOT fuel trim is not relevant due to the O2 sensor being ignored and the system operating in open loop.
@4:00 is perfection !
Can you tell us the main things you look for when examining an engine that comes in with a clogged cat? Does alcohol in gas cause that problem? If the engine is running fine with no misfires, is there anything else that you need to check for?
So when you figure out your exhaust is clogged & it is most likely the CAT. What do you do? Grind off the pipe? weld on a universal cat? Where's the cheapest place to do this generally?
My truck can't pull grades anymore. Codes I had = missfires, o2 heater, mafs, lean a/f, and more missfires. I checked/cleaned the plugs and wires. Good to go; got my engine power back & no more check engine light. But after getting warm (30minutes+ of driving)... I can't pull hills. Drops down to 50mph.
This ford has the vacuum regulated system so there wasn't anything in the scan data for the pressure. As for the o2 being functional, I didn't scope it, although I did watch scan data while unplugging the brake booster and drove the o2 lean and the response was great and it switches good around 2500 rpm along with bank 1.
@CHIBA280CRV I was not involved in this car other than the diagnosis. The owner took the car elsewhere for the repair.
If you measure the MAP reading key on engine off? That will measure baro pressure. While at wide open throttle, if the MAP raises above baro? That will also identify a likely restricted cat. Although this test only works on non turbo vehicles.
Thanks again Scanner and as always truly amazing!
My daughters 05 Ford 500 will only run momentarily with the throttle on the floor.
It has codes P2196 Oxygen sensor signal Biased stuck rich Bank 1 Sensor 1 and a P2198 which is the same code for Bank 2 sensor 1.
It has 10.3 PSI Fuel rail pressure but since the O2's are showing rich perhaps this is the problem?
I have 10 PSI at the fuel rail using live data at any RPM..
But it also has a P0191 Fuel Rail Pressure Sensor Circuit range performance code as well.
Sounds like sounds like a low volume fuel pressure to me. If fuel trims showing rich are you saying it negative fuel trims? If so then it's trying to add Fuel but can't because of low pressure. (Filter might be clogged) other rail pressure sensor is showing low because of not enough fuel I would bet
Love this Video
great video my friend
amazing :D from Peru
What typically makes a catalytic converter go bad? Rich fuel would make it overheat and then melt. How does burnt oil effect them? Will anything else contaminate it and cause it not to function properly
Could you also test for reversion with a vacuum gauge
I did have the o2 sensors in the 2 graph mode on a snap-on solus and same results during multiple WOT drives. Would you recommend any other testing that would be a smarter approach to one lean bank situation? Otherwise I will can have more info tomorrow unless I figure it out. Thanks.
Nice video. Very well done.
Hello Paul. I have question on this type of diagnostic using the o2 sensor data. Lets say you have a dual bank o2 sensor system and bank 1 (s1) reading is 800mv and bank 2 (s1) reading is 52mv at WOT. Would this indicate a fuel delivery issue? Would a MAF sensor problem cause both banks to be low? let me know when you get the chance. Thanks!
@westin1985 overly rich or lean ratios and misfiring, im sure oil burning doesn't help it either
@scannerdanner
cool video... hey, I have an issue that happen almost from one day to the next... 2000 firebird 3.8 5 speed.... @ first I thought it was the clutch because I would feel the car "sit" every other shift or when I took it over three thousand rpms. the first time I noticed something off was when I floored it and saw smoke... which it was weird because my car does not smoke.... then days later, again but lingering smell of any kind, especially burned clutch, it a rich mixture. So that's why I'm with the idea that it is the clutch or slave cylinder, but every gear shifts with no issue, no grinding, my clutch pedal is high and reacts normal, no vibrations, no hydraulic leaks. now, talking about the catalytic converter there is no rotten egg smell but twice now I've heard backfiring more predominant as I coast to a stop light. I don't hear it as loud as usual and the power is not really there, I also notice that it idles higher than normal....
with that said, does it sound like a clutch issue, a catalytic issue or a vacuum issue.... thank you for your time..
Simple diag, great video😏
Thanks! 👍
factory only! more than likely an aftermarket cat. (even direct fit) will set another cat. code within a few months.
My BMW X3 showed 25psi !!! Lean code, innactive sensor code and lots of steam out the back which I assume is fuel vapour
Thank you, I'm so glad I finally watched your channel I definitely subsrcibed
Car went to 20mph a year ago and have been hesitant to tackle it, though I suspected exhaust. After watching this it doesn't look horrible to test before marching forward. Car apparently had a long term severe misfire, then with the help of a lumpy tire it suddenly acted up before we got it changed.
If you do not have a backpressure gauge, you can test drive it with the O2 removed and see if your power gets better. Don't drive it long this way, just one wide open throttle run to see.
@@ScannerDanner thank you, that's what I was planning originally, but I did go buy a gauge to check it right. It's just a junker car and maybe 4 years left before rust gets to something critical.
Great video. Helped out alot
The squeaking isn't the intake it's the cat had it happened on my Ford Escape
You didn't rule out the muffler. Check the downstream o2 sensor hole with the meter. If low pressure, there is a restriction in the cat. If "high" pressure, the restriction is downstream from the cat.
If the restriction is downstream of the cat, it came from the cat. So replacing the cat and everything downstream of it is pretty typical. Or at least a visual inspection of the back of the cat to make sure there are no pieces missing. Of course you can drill a hole or remove the downstream O2 to test for this, I just found it not necessary in 99% of the times you will see this.
You Have to be careful removing an o2 sensor i did once and the threads came off resulting in a new o2 sensor.
I bought your book and i am loving it everyone buy his book its worth the money is it possible to down load the book or do we just keep the licence code for viewing purposes
no it is steps or counts on this design. No on question two, too many variables.
I didn't notice or pay attention to map on this but yes map voltage being high would also help to id this condition.
I appreciate the video boss! Quick question for you though... if 1.5 - 2 psi at idle and 6 7 psi at 2500 rpm is high, what should the pressures actually be at?
Near 0 for this test
You just can't assume the catty converter just by removing that o2 sensor and connecting the pressure gauge. You have to check the exhaust pressure going out from the catty converter. The restriction maybe further down the tail pipe.
The restriction is always the cat. I've never seen a muffler plugged up, that wasn't from the cat.
What you have to worry about is if pieces of the melted cat broke apart and logged themselves in the muffler. I've definitely seen that happen before. So when you sell the job, it gets a new cat and warn the customer about this possibility. A simple visual inspection of the rear of the cat is all you'll need once it's removed. Or just sell the exhaust system from the cat back.
had an impala with same motor. i replaced cats 2 times. had no power going up hill. got a tune up, and plugs had thick white crust on plugs. oh by the way i start rosedale may 27th.
great video man ..
What should the pressure reading be normally at idle and 3000 rpm?
Good vid thanks
Would it hurt to run the vehicle with the 2 front O2 sensors removed? I have a OBD II code reader will this find a problem with the fuel trim? What should I look for? Would too much ethanol in the fuel melt the cats? In Pa right now there should be no more than 10% of that garbage in the gas. The 97 Explorer is NOT a flex fuel vehicle. The more ethanol the hotter the combustion gets. Anyway excellant video. Could you not use a regular psi guage?
I had a nagging code P0171 P0174 p0300 p0304 p0306 on my 2001 GS 300 and the car would not go past 40... the Engine was loud and the car would have trouble starting... I changed the spark plugs, fuel filter and fuel pump at the tune of hundreds of dollars... Finally I tested the Ignition coils and the resistance was too high... The misfires (p0300, p0304 p0306) caused the oil to get into the CAT as well as making the car run lean and burning fuel in the cat resulted in a clogged cat that lead to the car not going past 40 mph... I was not going to get a new cat so I tried Lacquer thinner in a half tank of gas as well as dumping a can of throttle/ carb cleaner in the upstream (pre cat) 02 sensor hole... eventually it got better till it ran like new... The Lacquer thinner burns in the cat hotter than regular gasoline, burning the oil that is clogging it up... I saw it on Scotty kilmer and it worked for my situation... now the Risk is that the Throttle cleaner may have chemicals that don't go well with the metals in your cat or that the Lacquer thinner may damage seals in your fuel line... so they should be used with caution... however if you are going to change the cat why not clean it with Throttle cleaner first to see of it works? save 2 grand.
I had this happen to me on a 01 Grand Prix 3.8 k engine. Same symptoms but bad misfiring on cylinder 3 and a little less on 1 and 4 under wot. Aftermarket Ngk spark plugs was my presumed culprit but changing them didn't fix it with wires. Cat measures 10 psi+ at wot. No bueno. I wish the exhaust would have whistled like this one did.
I have an '05 Cobalt that had misfires due to a bad/faulty Ignition Coil Module because it kept over heating because of the foam that sits on top of it that is glued underneath the beauty lid cover on the engine. After installing the ICM I cut away the foam that was suffocating/covering the ICM and preventing it's ventilation fins from performing their function and I also drilled ventilation holes through the plastic engine cover. I suppose the misfires and extra fuel can destroy or at the least shorten the catalytic converters life expectancy. In-credible.
TU+SUB most definite
it is actually very simple. use a factory cat. only! aftermarket cats will continue to set P0420 codes
Thanks. I think ..Also another method is possible just remove o2 sensor and look at speed of car lf increased
for sure, this works as well
U can also tell by the bank1 and bank2 being the same
i love your video, i am actually on paid subscription . could you also instead of back pressure test test PIDS of dowstream O2 at 2500rpm, saw a video in which guy had bad cat and his B1S2 sensor at 2500rpm didn't have a flat line reading common on healty cat (usually close to 0.5V) but instead started following O2S1 sensor. Is that a good alternative test to prove cat is bad? To me seemed easier/faster method since he was watching on scan tools both upstream and dowstrem O2 sensors at 2500.
Remember a cat can be "bad" in two ways.
1. Lack of oxygen storage capability, but still provides good exhaust flow.
2. It is melted and restricting the exhaust.
In both cases the downstream O2 will mimic the upstream
So no, you cannot use a downstream O2 signal to determine if the exhaust is restricted.
Great question and thank you for the subscription!
i did not meant your answer was not right, with fast response. it is about you answer my question fast. sorry
Yea, goofy design, the only reason they put a vacuum line to the pulsator is in case the diaphragm ruptures. That is it, that is the only reason.
Sorry Paul but if your number are positive for example 800mv the vehicle is running lean cuz the computer is adding fuel to composave the plugged converter if it the number were negative it will be rich condition cuz the computer is substrating fuel
What is the back pressure supposed to be at idle, 1,2,3,4, and 5 thousand rpm? If the car was on a dyno how much horse power is robbed from a restricted exhaust per psi of back pressure. There must be some formula that can approximate the horsepower it takes to move a volume of air at a certain psi.
Gauge and adapter is from where? I guess you could use a compression/leakdown setup with a low pressure gauge?
Not sure? I'm sorry, but I do have one listed on my Amazon Affiliate page www.amazon.com/shop/scannerdanner
Enjoy your vids although admittedly much goes way over my head. As a shade-tree, backyard mechanic that just wants to save some money by diagnosing and repairing my own cars, can you recommend a scanner that will do more than just read DTC's and live data? There are SO many different scanners with many different price points and, for me, confusing descriptions that I'll turn to you for expert for guidance. Thanks.
I forgot to say, I CAN'T spend $2-300 on one.
Post this to my forum. It is free to join and you can gain insight on what others are using. www.scannerdanner.com/forum.html
nice info. but i would just pull out an 02 sensor. bada bing
grait job . you are grait teacher thanks a lot for scanner danner website
GOLD!
Thanks!!
How much was. That scanner& where'd you get it