Excellent troubleshooting! I'm not good at wiring, but when you said the heater and the fuel pump both related issues on separate circuits, i immediately thought of a grounding issue - that seems to usually be what causes weird gremlins like this. I had a weird grounding issue on my car where the headlights would randomly turn off and I'd lose dash lights. It turned out I didn't have one of the main grounds secured. Thanks again!
Very nice lesson as always. This also would indicate that the oil pressure switch/circuit is no good, as once the engine is running the relay can be taken out of the loop and it should still continue to run. I realize that I am commenting on an old video, but for anyone that comes across it should also be aware of the oil pressure switch, which you did address on operation in the beginning when looking on the diagram.
Great video. Your knowledge of electrical systems and how to diagnose them is awesome . You give easy to understand examples of how to diagnose and repair what seem to be difficult problems. I was a mechanic for ford for twenty years before falling at work and hurting my back. I miss it terribly. Your videos bring me back to a time when fixing automobiles was not only easy for me but fun also. Your enthusiasm is refreshing. Thank you for your videos they inspire me to want to rectify my ASE tests. Especially the L-1. And electrical. Those were my favorite vehicle problems to repair.
+Frank Senick that's awesome Frank! It's never too late to get back into it. Especially if you focus on electrical systems. It is a lot easier on your back :)
Want to information about it where the relays are in the Micra 1041 litre want to know where the relays are in the micro one day 04 too old for Micra 1 litre want to know where to realise that relays are in relays
so a question i seen the ground problem but as you shown in the wiring diagram the relay/oil pressure switch run in the same circuit so when the relay dropped out why did the fuel pump quit unless the oil pressure switch is not working or was the ground totally going in a open condition thanks hope you like questions i alway want to know
+Norman Bates actually it takes him longer to find faults than it should since he is teaching while diag'ing, but any good diag tech would have figured that out, it is not as hard as it looks, honestly. you just need to know theory and system set-up
Wonderful video. Learned a lot. My first reaction was to change the fuel pump, bad internal binding, etc. However, with proper testing and understanding theory of operation, I can see how my faulty reasoning would be an expensive lesson. Your methodical test procedure really made sense. Enjoyed following your explanation on the wiring diagram. Another thing, I learned was the importance of ground points. I didn't realize how critical they are and how they affect relays, etc. Thanks.
thank you so much for this! we just replaced the fuel pump and were still having this problem. so I searched and found this video and fixed it! awesome job, I'll be coming back to you for any other problems we have!
no, there are some frame mounted pumps but it is more common to be in the tank. some models offer an access cover in the trunk or rear seat area, which is nice.
Thanks! I've been watching several videos from you and I must say that not only your knowledge is great but also your teaching is superb!!! I'll keep coming back every time I have an issue with my Chevrolet Trans Sport, (Venture, Montana). 👍
Excellent excellent case study.. I was baffled in the beginning with the heater in the mix of things, that really through me a loop. Shared ground never cross my mind. Wiring digram interpretation is really key to figuring out what is going on within a circuit.
thanks mr. Paul for yuor videos, im in Mexico and i like all yuor videos you r a realy good teacher, now i understand my scanner and i will buy a scope. GOD bles you and your family
would you be able to pull the relay, if the fuel pump still runs then that would narrow down to relay. Thought process on that was like you said the oil switch would take over and still allow voltage to the pump.
Great video , shows that you have to look in odd places sometimes. One normally wouldn't think there was a larger current load on a relays control ground. Great info as always Paul.
great explanation! it just shows when you know your job , you make it look easy! it appears you are a seasoned mechanic! great job! process of elimination only works when you know your trade!~ where can we find mechanics like you ? Oh! one more thing, it takes a little time to diagnose!~ you took less than 30 minutes...outstanding!!~
@kenjackson1977 Do you have spark and injector pulse? Or does the engine run when you hot-wire the pump. All you said was the pump runs when you hot-wire it. I need to know to help you further.
Hey Paul Danner, Well Explanation for this Fuel Pump Circuit is very clear and making me to feel simple when the Faults Related to the Fuel Pressure issues come to me and im agree with your Motto " Don't Be A Part Changer" Thanks Forever Danner ❤❤❤❤❤
Your a very smart and knowledgable young man I really appreciate you putting this video out because I I have a similar problem with my nissan pathfinder.Thanks again I will like and share.GOD BLESS YOU.
+Will Rogers That is because sometimes it is for engine safety. This may be the exception or maybe safety is the exception. I'll leave it to scannerdanner to give the average percentages either way. I know it is a safety on older GM diesels of the 90's era. Least ways they won't run when that switch goes bad.
Loved the video walk-through, as well as the process of elimination you used to get to the root of the problem! I'm not a mechanic by even a loose interpretation of the term (I like to do simple maintenance like change the oil, brakes/rotors, spark plugs, etc on my e39 540i). What would you recommend as a way to find a good mechanic to work on a car? One that will diagnose problems like you did in the video. Most I've been to would simply replace a pump/relay/etc and "see if that works".
Paul,Guess I am asking the question from the perspective of being an owner/user of a Load Pro Dynamic Test Lead, and wondering if it would have revealed a bad ground from the terminal... perhaps I'll get a chance to test (or create a test environment to experiment and see if it will work)...
I know this video is old, but I'm confused about the relay... You said that oil pressure switch provides alternate power to the fuel pump once the engine is running and that you could pull the relay after it's running and it would stay running... So why does the relay switching off and on like that kill the engine? Obviously there is a problem there, but the oil pressure switch still should've kept it running... Edit: nevermind, I understand now. With that ground issue effecting the entire system (most likely), the oil pressure switch would also be loosing connection.
You were right in your initial idea. The only way this engine fuel pump would stop and start because of a relay ground problem is if the oil pressure switch was not working. The oil pressure switch get power from a fusible link and it bypasses around the relay and connects to the same fuse and on to the fuel pump. The Oil pressure switch has no ground to worry about. The fuel pump itself has a totally different ground than the relay itself.
Super cool case study. Reminds me if your similar issue with the s6 Audi and how it had a loose nut on the firewall ground. Being a Euro specialist you have no idea how many times I see that.
Some nice multiplexed circuits over long spans. Pulse width modulated fuel control valves on CNG engines. Gas mass flow sensors. Coil on plug ignition with a separate module from the ecm
Is the oil pressure switch not working? Why didn't current keep flowing to the fuel pump through the alternate power feed (oil pressure switch) when the fuel pump relay was turning off? I think there must have been another problem here in addition to the bad ground on the control circuit of the fuel pump relay.
Hey Dan have a question I have a 1999 GMC safari van Meyrou fuel pump relay gets extremely hot could it be that it's holding too much load because the oil pressure switch is bad thank you
A bazillion $ scanner, schools and training to find a Chevy ground fault.... priceless...! but... it was a stovebolt to begin with and would never ever own one newer than '60's..great video SD.... I loved it, your diagnostic skills are greatly admired here...73 and still wrenching...but not on those dogs...
thanks my friend. I have much respect for my elders. I hope I live long like you to see my grand children. May God bless you and your family and continue to bless your hands and your mind as you continue in this field.
Hey SD thanks for that...You know of course I was not being disparaging in any way of your talent and training..love and appreciate your efforts you use to educate us old school dummies to the new tech..who would have guessed it in high school auto classes in the 50's working on Ford flat-heads and Chevy stovebolts it would have come to this ..?
@ScannerDanner If the FP relay turns on and the injectors fire you need to replace the ignition module. I know, I know, "but I have spark" is what you are thinking. Listen, these modules will fail in that it will still control the coil, but not send the reference pulse (0-5v square wave) on the purple-white wire to the ECM. Without this signal the ECM will not see an RPM signal and will not fire the injectors and will not run the pump.
Dan excellent video wondering? Would a ground V-Drop test have been a valid test to prove the existence of a bad chassis/signal ground at the OBDII connector terminals 4 and 5??? and... where is your e-book link?
You said in your video that the fuel pump oil pressure switch is not there to protect the engine but to serve as an alternate route in which the current could travel. My question is will the fuel pump oil pressure switch keep the vehicle from starting?
actually even with this bad ground in theory shouldn't oil pressure switch take over control when relay loses it ground and keep car running although if those are computer grounds too then if computer is losing ground too and effecting control of other circuits that real reason car wont stay running or does car have bad oil pressure switch too ? makes u wonder what would happen if u pulled out relay after u fixed the ground
@ScannerDanner Another clue to this problem is when you first turn the key on you should still get a fuel pump "prime". This is the ECM turning the FP relay on for a second to bring fuel pressure up. After this "prime" the ECM will NOT turn the FP relay back on until it receives an RPM signal (on the purple-white ref. wire). If you do not have a "prime" happening when you first tune key on, then we are barking up the wrong tree. I can still help you though.
at 17:30 you said the ground should be around 0, is that because the scope is measuring the potential difference between the power and ground and if it were working correctly and didnt have resistance it would be around 0 volts?
Great case study!!! You’re the best too bad you’re not in the Los Angeles area, it would be a pleasure to let you diagnose my car problems but I’m learning a lot from you great guys! (Scanner, Eric o, Ivan)
This was a main block ground problem so it wouldn't matter where the power was coming from (relay or oil pressure switch), the problem would still be there.
good question, with the bad block ground nothing was really working correctly. I have to look at the diagram again to give you a better answer than this.
Im now curious given the video and my current issue if there was no oil pressure if the circuit/ecm would shut down the fuel pump. My fuel pump is having issues and ive seen when such happens the oil pressure gauge will read almost max pressure. Am wondering if the fuel pump and oil pressure were tied together purposely as a safety measure
Hey day. I was watching this video on fuel relay issues on gmc. Upon checking my relay I thought that when I unplug the relay the oil pressure switch should keep the fuel pump running. And mine shut rite down. So I replaced the oil switch. And tried the test again And when I pulled the relay out it shut down. Why would that happened??? Thinking the oil switch would keep it running.
I wish I had an easy answer for you. Unfortunately it is hard to find a good diagnostic tech in this field. Most mechanics are parts changers. A suggestion is go to iATN and search iATN's Auto Repair Shop Finder. This isn't going to guarantee that you find a good diagnostic tech, but I think it will increase your chances.
why when the relay was turn off the oil swicht dindt do its job and keep the pump energize???, was the oil swicht bad or it was energizing but the pump keep turn it off because of the bad main ground?
great video just bought a 93 f150 runs like a dream.but after 30-40 min it starts stumbling and cutting off i change fuel fliter and pump and still do the same thing what u thing costing the problem.live in the bahamas
cool! ...a question: when koeo, why is the green line(power for the relay`s control side)behaving exactly the same way as the yellow line(relay`s control ground)...when you turn on the heater...and then when you wiggle that bad ground?...my guess: bcus they both are as one, since there is no power to the green line with the koeo
probably going to buy this ebook once paul replies to a question i emailed. anyone have any other recommended youtube channels or ebooks that are worth watching or buying?
one last thnig! a good mechanic, listens to the customer~ it's called communication! it's like a doctor patient relationship~ So the customer was correct in his explaination of the cause of pump failure. didn't show on diagram sometimes it won't. great meachanics are the best trouble shooters!!
Hello, I have a 77 911S, the fuel pump, (new), keeps burning out the relays, maybe I should. check the ground, or can I do it with a meter? Thanks Russ
burning out the relay for the fuel pump? How is the connector going to the relay? If it is corroded, this will equal heat from resistance in an unwanted location and can definitely burn things out.
1985 honda prelude 1.8 automatic, fuel pump not working, pulled it tapped to 12 volt source works, tested wire leads to fuel pump no power, pulled and replaced fuel pump relay switch, still no power, car starts after pumping on gas pedal, but under load in drive began to stutter and shuts down if not on gas pedal, just purchased a painless diy dedicated fuel pump relay wiring harness, all fuses are good, any suggestions, before I install wiring harness. Thanks
i guess the best way to learn faster is to create faults on our own cars. The waveforms makes electricity visual instead of a invisible theory. I love it !!!!
scanner, my 88 mustang 5.0 wont prime either, i jumped the self test to ground and it turned on ran like that to get to work, tried it few days later now it doesnt even prime with it jumpered to grnd. also i feel alot of current drawing out the jmpr wire when its grnd. i know i should just replace the pump and relay but call me cheep but y would it work that way then stop?
Further to my first question, the following is my real problem:I am driving the Ford Mondeo for 12 years now. Its a 2004 model 2liter petrol. It gave me excellent service. Then all of a sudden after 175 000 km, on the long road it started to loose power on uphill stretches and eventually comes to a stand still. Waiting for 10 minutes or so, start it again and then it will go for 10 km or so. It seems that as “something” gets hot it causes the problem. I at first thought it was the petrol pump but then someone told me, no, rather buy a new Fuel Pump Relay which I did and it then worked like a dream for 18 months. Then it started again with the same old story. Remember now the first relay worked for 12 years over 175 000 km, and the second one 18 months and only about 5000 km. I cannot tell you what really gets hot to have to cool down sothat when you start it it will go OK for a awhile. The Relay is supposed to work also the Air conditioner, ECC power (what ever that is) , High Beam lights, windscreen wipers, battery saver, fuel feed, the Horn, rear window wiper. After I established this I switched off all these “additional” uses (except the battery saver what ever that may be) and assumed it will then work the fuel pump only. No joy..... I have ordered a new relay but has not fitted it yet because driving in town on very short distances it gives no problems at all. Is there not perhaps a short causing not enough power to go the the fuel pump. But that does not explain why it stops working when I dont know what, gets hot. What is your opinion. I will greatly appreciate your views. Thanks
TCM ATA relay which is controlling with "-" from TCM. Black probe to pin on TCM and Red on relay "-" side. I got 1.5V (on ign.key on only). Is it the bad ground? I found how to check bad ground later on your channel. Thank you for all these videos🎉
That is one sweet capture. I was cool to see that the fp would operate with 4v on the ground. Very cool patern. One look at the ground voltage on the yellow trace, that was too cool
Excellent diagnostics Dan but seeing you pierce wires freaks me out. I live in the damp northeast and greenitis is a death sentence to a wiring harness. I know those tools are easier than rigging up backprobe taps and bridges but those little holes cause BIG problems. That said keep these great videos coming.
Great video. Nice to see what you can do with a scope. I have been doing this for years with a test light and a cotter pin. I may use a multimeter if I get really hard up. Granted this is an instructional video but why not use a cotter pin to ground out the control side of the relay and verify (a) relay works, (b) pump and load side work? All diagnostics in the video are great, I'm not trying to criticize here but a relay needs 2+ and 2- to work which is basic electrical....
+Dalton Jones It should be constant, not sure if it is an ignition or battery power though. But it needs to be powered all the time for for sure with the key on
+Dalton Jones It should be constant, not sure if it is an ignition or battery power though. But it needs to be powered all the time for for sure with the key on
+ScannerDanner code 54. When everything is stock, it is hard to start when it is cold. I can jump a power lead from the battery to the fuel pump lead and it will start right up and run great. I can unhook that jumper and it still runs great. Starts right back up while still warm. But when it cools back down, hard to start again
paul you said that the oil press swith is a back up feed for the fuel pump in case the relay fails, but in the diagram im seen that that switch is normally close, with no oil pressure or engine off the switch is close, and with oil pressure the switch is open, and if the switch is open with the engine running, how can it be a back up feed for the fuel pump?, i think that what the switch does is energize the fuel pump just before it start cranking the engine to have good fuel pressure for a quick start
The crank signal is simply a fused tap into the heavy purple starter solenoid wire that runs along the RH valve cover. It tells the ECM the engine is cranking so it can calculate fuel delivery and spark timing accordingly. The crank signal also tells the ECM to keep the fuel pump relay energized until you have oil pressure at which time the oil pressure switch takes over fuel pump power supply responsibilities.
I thought I answered this. Maybe it was someone else. You want to have battery voltage. Whatever system voltage is, is what your fuel pump power feed should be. However, there are variables to this. If the pump is pulse width modulated, then there can be lower voltage showing when using a DMM but even on these systems they run full speed during cranking.
Got a question for you. Buddy has a 97 Dakota with a v8. Went to leave the house one morning and truck wouldn't start. Replaced fuel pump still no start. Fuel pump relay and fuse are good. Plenty of spark. Took bed off of truck and no power to fuel pump. Any ideas
Jeramiah Kemper how did you test the relay? just because it clicks does not mean it is good. First you need to do voltage measurements at the relay before chasing a broken wire in the harness between the pump and relay.
Jeramiah Kemper Okay, so the relay is good, but that doesn't mean your load side feed is good going to and from the fuel pump relay. With the relay removed, you should have two pins that are "hot"during cranking. Do you?
You would only see the amp draw on the initial prime after the engine runs the voltage comes from the alternator so you won’t see it at the battery neg cable
@spelunkerd Nice, I have never heard that quote. I like it too. The oil psi switch is simply there as a backup in case the relay fails. Of course the other side of that oil psi switch runs the oil psi gauge or light, so it serves two functions. I don't know why GM felt the need to backup the FP relay. No one else is doing that. Seems like a waste of copper wire to me. They must have had a lot of problems with this circuit early on?
My 2001 Silverado, when cranking it will turn over "spinning good' Turn switch off restart cranking it will start the second, third or fourth try. when started it idles and run good, no problems until turning off and re starting. can it be the fuel pump?
Love this video ! I have one question. Had a car in the other day and customer complained of long crank with his chev lumina. Did not get a fuel pump prime when key was turned on. noticed fuel pump wire dia was nearly the same as the car on this video.I noticed the red wire @ relay is the fuel prime. Where does that red wire get its power from ? didn't get much time to look at the car but gonna have to dive in Monday morning.thanks.
@ScannerDanner That sounds a lot like a quote from Isaac Newton. It went like this, "If I have seen farther, it was by standing on the shoulders of giants...." I love that quote, and I love standing on shoulders, ha ha. Why is that backup circuit from the oil pressure switch there?
@fivefortyeye540i Thank you, this one was a little tricky to film. There are so many different directions I could have taken this. Hopefully it was clear and not cluttered with too much info.
It was already at a few shops and they couldn't fix it. If it was brought to me when I was in the field, it would have been an hour diagnostic time then another hour on the repair. Garage rates are about $100 or so per hour.
You are awesome Paul. If i buy your e-book i'll have some kind of guide to learn how to diagnose problems like you did? I'm a begginer mechanic and current(and begginer) student of Electronic Engineering and i'm interested in learn this stuff. Thank you for your excellent videos!
@CoolasIce2 I just checked out that scope. It is an old analog scope. It will do want you want but you will have problems with "glitch" captures because there is no play back. I would recommend you go on ebay and buy a used Vantage (not pro, unless you can afford it)). It is a graphing multimeter and will get you by for awhile. Plus the data base in the tool is unmatched in this field. I have had students pick them up for around $200
I enjoyed this knowledge fully can I fly you to Vegas to troubleshoot my 1995 Buick century wagon at this point I’m atleast 80% sure it’s a wiring issue
I definitely have spark after watching this I am checking fuel pressure tomorrow it’s a 3100 odb1 and computer wont tell me anythingi have trouble with hard start once starts bogs and idles badly then if an drive a mile or so all seems well until next start usually
Great Video and Thank you. But I have a question pls. My 1994 Cadillac Fleetwood Brougham (LT1 engine) , runs without the Fuel Pump Relay plugged in, I demonstrated that for sure. But with the fuel pump Relay plugged in, my AC shuts off as I accelerate to 50 to 70 mpg, I did the fuel test while driving, and the fuel pressure never reached 41psi, the minimum specification for the fuel pressure. The fuel pressure hovered at about 34 to 35psi at low and high speeds. Could this problem be a ground issue, as you demonstrated with this video, or could this be a fuel pump problem that needs to be replaced. If you think this is a ground issue, where would I find the ground in the car that needs to fixed. Thank you for your time and response.
+Sam Rafeedie If you are saying the fuel psi should be 41 psi at WOT and it is not increasing, then yes a poor power or ground to the pump can cause low psi but most likely you have a failing fuel pump.
ScannerDanner Ok so I have no clue if you will see this or not but my husband basically has a switch that turns on his fuel pump... It was like that when we got the truck. The other day on the way to work he went through a big puddle and his truck died. He found that the fuse in the switch was blown. It keeps blowing every time after running for about 10 mins. Usually if he hits a bump or is turning. It keeps on blowing. I know nothing about vehicles but wanted to ask if maybe you knew maybe what's going on. It says 15 a for the fuses we have been replacing. I don't understand why the fuse keeps blowing.
Hi. I know this may not be related at all but felt maybe your knowledge could help me a little. My husband was driving to work the other day and drove through a puddle of water and his truck died. He has a switch that turns his fuel pump on. It was like that when we got the truck. Well he seen that the fuse in the switch was blown so he replaced it. It will run for about 10 minutes and then the fuse for the switch will blow again. It keeps blowing over and over. We tried replacing the switch to no avail. It keeps doing it. I don't know much about cars to begin with just thought maybe you might have an idea.
It is becoming more and more difficult to answer questions here. I have 80,000 people asking me for help now. So I have created a forum to help you guys better. It is free to join and we can exchange pictures, wiring diagrams and waveforms if needed to help guide you through the process of troubleshooting your vehicle. Thank you so much! Hope to see you there. Paul Danner (ScannerDanner) www.scannerdanner.com/forum/post-your-repair-questions-here.html
![New Fuel Pump - Still No Fuel Pressure - Now What? [2012 Ford E350]](http://i.ytimg.com/vi/GJ9O8pTkK4w/mqdefault.jpg)
Excellent troubleshooting! I'm not good at wiring, but when you said the heater and the fuel pump both related issues on separate circuits, i immediately thought of a grounding issue - that seems to usually be what causes weird gremlins like this. I had a weird grounding issue on my car where the headlights would randomly turn off and I'd lose dash lights. It turned out I didn't have one of the main grounds secured. Thanks again!
Very nice lesson as always. This also would indicate that the oil pressure switch/circuit is no good, as once the engine is running the relay can be taken out of the loop and it should still continue to run.
I realize that I am commenting on an old video, but for anyone that comes across it should also be aware of the oil pressure switch, which you did address on operation in the beginning when looking on the diagram.
Great video. Your knowledge of electrical systems and how to diagnose them is awesome . You give easy to understand examples of how to diagnose and repair what seem to be difficult problems. I was a mechanic for ford for twenty years before falling at work and hurting my back. I miss it terribly. Your videos bring me back to a time when fixing automobiles was not only easy for me but fun also. Your enthusiasm is refreshing. Thank you for your videos they inspire me to want to rectify my ASE tests. Especially the L-1. And electrical. Those were my favorite vehicle problems to repair.
+Frank Senick that's awesome Frank! It's never too late to get back into it. Especially if you focus on electrical systems. It is a lot easier on your back :)
Want to information about it where the relays are in the Micra 1041 litre want to know where the relays are in the micro one day 04 too old for Micra 1 litre want to know where to realise that relays are in relays
2oo4 micra 1 liter were are relays
so a question i seen the ground problem but as you shown in the wiring diagram the relay/oil pressure switch run in the same circuit so when the relay dropped out why did the fuel pump quit unless the oil pressure switch is not working or was the ground totally going in a open condition thanks hope you like questions i alway want to know
Fella, I gotta say you know your stuff. I don't think very many people would have figured that one out. Thanks.
+Norman Bates actually it takes him longer to find faults than it should since he is teaching while diag'ing, but any good diag tech would have figured that out, it is not as hard as it looks, honestly. you just need to know theory and system set-up
Wonderful video. Learned a lot. My first reaction was to change the fuel pump, bad internal binding, etc. However, with proper testing and understanding theory of operation, I can see how my faulty reasoning would be an expensive lesson. Your methodical test procedure really made sense. Enjoyed following your explanation on the wiring diagram. Another thing, I learned was the importance of ground points. I didn't realize how critical they are and how they affect relays, etc. Thanks.
thank you so much for this! we just replaced the fuel pump and were still having this problem. so I searched and found this video and fixed it! awesome job, I'll be coming back to you for any other problems we have!
no, there are some frame mounted pumps but it is more common to be in the tank. some models offer an access cover in the trunk or rear seat area, which is nice.
but, shouldn` t that oil pressure switch take over when the relay fails???
being able to see that relay open and close was pretty helpful. i want to order a set of clear relays to help with diagnoses
That was totally cool!! Seeing the relay open and close and the diagnostic screen spikes was awesome! Thank you!
My El camino has a clear distributor it is awesome
Thanks! I've been watching several videos from you and I must say that not only your knowledge is great but also your teaching is superb!!!
I'll keep coming back every time I have an issue with my Chevrolet Trans Sport, (Venture, Montana). 👍
Brilliant video, very good example of how to use a scope and diagnose either a bad ground or supply feed. Brill!
Excellent excellent case study.. I was baffled in the beginning with the heater in the mix of things, that really through me a loop. Shared ground never cross my mind. Wiring digram interpretation is really key to figuring out what is going on within a circuit.
This is the best educative video I've ever seen in this site,You are a real professional ,Thanks for helping.
thanks mr. Paul for yuor videos, im in Mexico and i like all yuor videos you r a realy good teacher, now i understand my scanner and i will buy a scope. GOD bles you and your family
this is a perfect example of why i think your videos are the best--> well thought out real world troubleshooting!!!
would you be able to pull the relay, if the fuel pump still runs then that would narrow down to relay. Thought process on that was like you said the oil switch would take over and still allow voltage to the pump.
Great video , shows that you have to look in odd places sometimes. One normally wouldn't think there was a larger current load on a relays control ground.
Great info as always Paul.
great explanation! it just shows when you know your job , you make it look easy! it appears you are a seasoned mechanic! great job! process of elimination only works when you know your trade!~ where can we find mechanics like you ? Oh! one more thing, it takes a little time to diagnose!~ you took less than 30 minutes...outstanding!!~
@kenjackson1977 Do you have spark and injector pulse? Or does the engine run when you hot-wire the pump. All you said was the pump runs when you hot-wire it. I need to know to help you further.
Hey Paul Danner, Well Explanation for this Fuel Pump Circuit is very clear and making me to feel simple when the Faults Related to the Fuel Pressure issues come to me and im agree with your Motto " Don't Be A Part Changer"
Thanks Forever Danner ❤❤❤❤❤
Your a very smart and knowledgable young man I really appreciate you putting this video out because I I have a similar problem with my nissan pathfinder.Thanks again I will like and share.GOD BLESS YOU.
Thank you my friend, God bless you too!
@ScannerDanner TY!!! For years I always thought the oil pressure switch was for safety. Clearly it is in parallel with the circuit.
+Will Rogers you welcome! thank you
+Will Rogers That is because sometimes it is for engine safety. This may be the exception or maybe safety is the exception. I'll leave it to scannerdanner to give the average percentages either way. I know it is a safety on older GM diesels of the 90's era. Least ways they won't run when that switch goes bad.
Loved the video walk-through, as well as the process of elimination you used to get to the root of the problem! I'm not a mechanic by even a loose interpretation of the term (I like to do simple maintenance like change the oil, brakes/rotors, spark plugs, etc on my e39 540i).
What would you recommend as a way to find a good mechanic to work on a car? One that will diagnose problems like you did in the video. Most I've been to would simply replace a pump/relay/etc and "see if that works".
I can't wait to get paid and buy your ebook. I've been watching your videos and they're great!
Paul,Guess I am asking the question from the perspective of being an owner/user of a Load Pro Dynamic Test Lead, and wondering if it would have revealed a bad ground from the terminal... perhaps I'll get a chance to test (or create a test environment to experiment and see if it will work)...
I know this video is old, but I'm confused about the relay... You said that oil pressure switch provides alternate power to the fuel pump once the engine is running and that you could pull the relay after it's running and it would stay running... So why does the relay switching off and on like that kill the engine? Obviously there is a problem there, but the oil pressure switch still should've kept it running...
Edit: nevermind, I understand now. With that ground issue effecting the entire system (most likely), the oil pressure switch would also be loosing connection.
You were right in your initial idea. The only way this engine fuel pump would stop and start because of a relay ground problem is if the oil pressure switch was not working. The oil pressure switch get power from a fusible link and it bypasses around the relay and connects to the same fuse and on to the fuel pump. The Oil pressure switch has no ground to worry about. The fuel pump itself has a totally different ground than the relay itself.
Super cool case study. Reminds me if your similar issue with the s6 Audi and how it had a loose nut on the firewall ground. Being a Euro specialist you have no idea how many times I see that.
Some nice multiplexed circuits over long spans. Pulse width modulated fuel control valves on CNG engines. Gas mass flow sensors. Coil on plug ignition with a separate module from the ecm
Is the oil pressure switch not working? Why didn't current keep flowing to the fuel pump through the alternate power feed (oil pressure switch) when the fuel pump relay was turning off? I think there must have been another problem here in addition to the bad ground on the control circuit of the fuel pump relay.
There are main computer grounds on that same stud. There was no other problems with this vehicle
Paul,would the fuel pump feed wire show high amperage if it was intermittently touching ground?
Would you be able to identify the bad ground by voltage drop from relay control ground to battery negative?
Hey Dan have a question I have a 1999 GMC safari van Meyrou fuel pump relay gets extremely hot could it be that it's holding too much load because the oil pressure switch is bad thank you
A bazillion $ scanner, schools and training to find a Chevy ground fault.... priceless...! but... it was a stovebolt to begin with and would never ever own one newer than '60's..great video SD.... I loved it, your diagnostic skills are greatly admired here...73 and still wrenching...but not on those dogs...
thanks my friend. I have much respect for my elders. I hope I live long like you to see my grand children.
May God bless you and your family and continue to bless your hands and your mind as you continue in this field.
Hey SD thanks for that...You know of course I was not being disparaging in any way of your talent and training..love and appreciate your efforts you use to educate us old school dummies to the new tech..who would have guessed it in high school auto classes in the 50's working on Ford flat-heads and Chevy stovebolts it would have come to
this ..?
@ScannerDanner If the FP relay turns on and the injectors fire you need to replace the ignition module. I know, I know, "but I have spark" is what you are thinking. Listen, these modules will fail in that it will still control the coil, but not send the reference pulse (0-5v square wave) on the purple-white wire to the ECM. Without this signal the ECM will not see an RPM signal and will not fire the injectors and will not run the pump.
Dan excellent video wondering? Would a ground V-Drop test have been a valid test to prove the existence of a bad chassis/signal ground at the OBDII connector terminals 4 and 5??? and... where is your e-book link?
Don't fuel pumps make some noise to just show they are operating?
Is it possible to determine a faulty pump based on speed, calculating from the humps? Or based on pattern only?
Great interpretation of the scope readings. Gotta love Danner if he's on You Tube or any where else!!
You said in your video that the fuel pump oil pressure switch is not there to protect the engine but to serve as an alternate route in which the current could travel. My question is will the fuel pump oil pressure switch keep the vehicle from starting?
actually even with this bad ground in theory shouldn't oil pressure switch take over control when relay loses it ground and keep car running although if those are computer grounds too then if computer is losing ground too and effecting control of other circuits that real reason car wont stay running or does car have bad oil pressure switch too ? makes u wonder what would happen if u pulled out relay after u fixed the ground
@ScannerDanner Another clue to this problem is when you first turn the key on you should still get a fuel pump "prime". This is the ECM turning the FP relay on for a second to bring fuel pressure up. After this "prime" the ECM will NOT turn the FP relay back on until it receives an RPM signal (on the purple-white ref. wire).
If you do not have a "prime" happening when you first tune key on, then we are barking up the wrong tree. I can still help you though.
hi danner, how do you translate the measures from the multimeter and clap meter, to convert amps???
at 17:30 you said the ground should be around 0, is that because the scope is measuring the potential difference between the power and ground and if it were working correctly and didnt have resistance it would be around 0 volts?
Great case study!!! You’re the best too bad you’re not in the Los Angeles area, it would be a pleasure to let you diagnose my car problems but I’m learning a lot from you great guys! (Scanner, Eric o, Ivan)
@CoolasIce2 Im not sure, I'll look into it when I get a chance. I think any scope is better than no scope but then again there is some crap out there.
This was a main block ground problem so it wouldn't matter where the power was coming from (relay or oil pressure switch), the problem would still be there.
good question, with the bad block ground nothing was really working correctly. I have to look at the diagram again to give you a better answer than this.
Im now curious given the video and my current issue if there was no oil pressure if the circuit/ecm would shut down the fuel pump. My fuel pump is having issues and ive seen when such happens the oil pressure gauge will read almost max pressure. Am wondering if the fuel pump and oil pressure were tied together purposely as a safety measure
It will not, it's simply a bypass circuit. Maybe old, old designs when this was first developed. But that's not what this one does.
Excellent piece of methodical diagnostic work 👍🏻👍🏻👍🏻
I need some help my corsa lite 1.4 model 2005 if start the ignition is hard and the petrol ceralator sometimes no power
Good Troubleshooter, Good Teacher - Thank you very much
Hey day. I was watching this video on fuel relay issues on gmc. Upon checking my relay I thought that when I unplug the relay the oil pressure switch should keep the fuel pump running. And mine shut rite down. So I replaced the oil switch. And tried the test again And when I pulled the relay out it shut down. Why would that happened??? Thinking the oil switch would keep it running.
I wish I had an easy answer for you. Unfortunately it is hard to find a good diagnostic tech in this field. Most mechanics are parts changers. A suggestion is go to iATN and search iATN's Auto Repair Shop Finder. This isn't going to guarantee that you find a good diagnostic tech, but I think it will increase your chances.
why when the relay was turn off the oil swicht dindt do its job and keep the pump energize???, was the oil swicht bad or it was energizing but the pump keep turn it off because of the bad main ground?
great video just bought a 93 f150 runs like a dream.but after 30-40 min it starts stumbling and cutting off i change fuel fliter and pump and still do the same thing what u thing costing the problem.live in the bahamas
SuperClutchy 1988 dodge 3.0
Fascinating Paul you should have been a forensic Detective this was so interesting
Hello, i have a problem with a 95 s10 ,...ir sends ground to my fuel pump fuse
cool! ...a question: when koeo, why is the green line(power for the relay`s control side)behaving exactly the same way as the yellow line(relay`s control ground)...when you turn on the heater...and then when you wiggle that bad ground?...my guess: bcus they both are as one, since there is no power to the green line with the koeo
Because the power for the control is coming directly from the computer which is also being affected by a poor ground. Make sense?
probably going to buy this ebook once paul replies to a question i emailed. anyone have any other recommended youtube channels or ebooks that are worth watching or buying?
one last thnig! a good mechanic, listens to the customer~ it's called communication! it's like a doctor patient relationship~ So the customer was correct in his explaination of the cause of pump failure. didn't show on diagram sometimes it won't. great meachanics are the best trouble shooters!!
How can you load a bad ground? Does current flow through a bad ground?
Dan... Freakin Genius!!!!!! This helped save my 89 Regal from the crusher....
Bad ground on the transmission?
Hello, I have a 77 911S, the fuel pump, (new), keeps burning out the relays, maybe I should. check the ground, or can I do it with a meter? Thanks Russ
burning out the relay for the fuel pump? How is the connector going to the relay? If it is corroded, this will equal heat from resistance in an unwanted location and can definitely burn things out.
1985 honda prelude 1.8 automatic, fuel pump not working, pulled it tapped to 12 volt source works, tested wire leads to fuel pump no power, pulled and replaced fuel pump relay switch, still no power, car starts after pumping on gas pedal, but under load in drive began to stutter and shuts down if not on gas pedal, just purchased a painless diy dedicated fuel pump relay wiring harness, all fuses are good, any suggestions, before I install wiring harness. Thanks
i guess the best way to learn faster is to create faults on our own cars. The waveforms makes electricity visual instead of a invisible theory. I love it !!!!
scanner, my 88 mustang 5.0 wont prime either, i jumped the self test to ground and it turned on ran like that to get to work, tried it few days later now it doesnt even prime with it jumpered to grnd. also i feel alot of current drawing out the jmpr wire when its grnd. i know i should just replace the pump and relay but call me cheep but y would it work that way then stop?
where is located the ground?
Further to my first question, the following is my real problem:I am driving the Ford Mondeo for 12 years now. Its a 2004 model 2liter petrol. It gave me excellent service.
Then all of a sudden after 175 000 km, on the long road it started to loose power on uphill stretches and eventually comes to a stand still. Waiting for 10 minutes or so, start it again and then it will go for 10 km or so. It seems that as “something” gets hot it causes the problem.
I at first thought it was the petrol pump but then someone told me, no, rather buy a new Fuel Pump Relay which I did and it then worked like a dream for 18 months. Then it started again with the same old story. Remember now the first relay worked for 12 years over 175 000 km, and the second one 18 months and only about 5000 km.
I cannot tell you what really gets hot to have to cool down sothat when you start it it will go OK for a awhile. The Relay is supposed to work also the Air conditioner, ECC power (what ever that is) , High Beam lights, windscreen wipers, battery saver, fuel feed, the Horn, rear window wiper. After I established this I switched off all these “additional” uses (except the battery saver what ever that may be) and assumed it will then work the fuel pump only. No joy.....
I have ordered a new relay but has not fitted it yet because driving in town on very short distances it gives no problems at all.
Is there not perhaps a short causing not enough power to go the the fuel pump.
But that does not explain why it stops working when I dont know what, gets hot.
What is your opinion. I will greatly appreciate your views.
Thanks
@silkylove1000 if the car is running fine and your fuel psi is good i wouldn't worry about it. the rpm test has some gray areas if you ask me.
TCM ATA relay which is controlling with "-" from TCM. Black probe to pin on TCM and Red on relay "-" side. I got 1.5V (on ign.key on only). Is it the bad ground?
I found how to check bad ground later on your channel.
Thank you for all these videos🎉
That is one sweet capture. I was cool to see that the fp would operate with 4v on the ground. Very cool patern. One look at the ground voltage on the yellow trace, that was too cool
thanks brother
Excellent diagnostics Dan but seeing you pierce wires freaks me out. I live in the damp northeast and greenitis is a death sentence to a wiring harness. I know those tools are
easier than rigging up backprobe taps and bridges but those little holes cause BIG problems. That said keep these great videos coming.
Where's the main ground located?
Great video. Nice to see what you can do with a scope. I have been doing this for years with a test light and a cotter pin. I may use a multimeter if I get really hard up. Granted this is an instructional video but why not use a cotter pin to ground out the control side of the relay and verify (a) relay works, (b) pump and load side work? All diagnostics in the video are great, I'm not trying to criticize here but a relay needs 2+ and 2- to work which is basic electrical....
does that orange lead going into the relay constant hot or is it switched? I have no current going to my fuel pump relay on my 1989 Camaro 305 tbi
+Dalton Jones It should be constant, not sure if it is an ignition or battery power though. But it needs to be powered all the time for for sure with the key on
+Dalton Jones It should be constant, not sure if it is an ignition or battery power though. But it needs to be powered all the time for for sure with the key on
+ScannerDanner I ran constant power to the orange wire on the fuel pump relay and it makes the fuel pump run constantly.
+ScannerDanner code 54. When everything is stock, it is hard to start when it is cold. I can jump a power lead from the battery to the fuel pump lead and it will start right up and run great. I can unhook that jumper and it still runs great. Starts right back up while still warm. But when it cools back down, hard to start again
if current is constant into the relay, the output stays on and the fuel pump will keep running
paul you said that the oil press swith is a back up feed for the fuel pump in case the relay fails, but in the diagram im seen that that switch is normally close, with no oil pressure or engine off the switch is close, and with oil pressure the switch is open, and if the switch is open with the engine running, how can it be a back up feed for the fuel pump?, i think that what the switch does is energize the fuel pump just before it start cranking the engine to have good fuel pressure for a quick start
It is a normally open switch. They stopped using it as a back-up around 2002-2004 depending on the model
The crank signal is simply a fused tap into the heavy purple starter solenoid
wire that runs along the RH valve cover. It tells the ECM the engine is
cranking so it can calculate fuel delivery and spark timing accordingly. The
crank signal also tells the ECM to keep the fuel pump relay energized until you
have oil pressure at which time the oil pressure switch takes over fuel pump
power supply responsibilities.
Mondeo Ghia 2004 2 liter petrol: What must the voltage be entering the fuel pump? What must the minim strength (voltage) be of the battery?
I thought I answered this. Maybe it was someone else. You want to have battery voltage. Whatever system voltage is, is what your fuel pump power feed should be. However, there are variables to this. If the pump is pulse width modulated, then there can be lower voltage showing when using a DMM but even on these systems they run full speed during cranking.
Similar to the nut that came lose on that Audi you were doing. Maybe the factory should put some loctite on those ground connection nuts.
Got a question for you. Buddy has a 97 Dakota with a v8. Went to leave the house one morning and truck wouldn't start. Replaced fuel pump still no start. Fuel pump relay and fuse are good. Plenty of spark. Took bed off of truck and no power to fuel pump. Any ideas
Jeramiah Kemper how did you test the relay? just because it clicks does not mean it is good. First you need to do voltage measurements at the relay before chasing a broken wire in the harness between the pump and relay.
ScannerDanner plugged relay into horn slot and horn works with relay from fuel pump slot
Jeramiah Kemper Okay, so the relay is good, but that doesn't mean your load side feed is good going to and from the fuel pump relay.
With the relay removed, you should have two pins that are "hot"during cranking. Do you?
ScannerDanner not yet. The truck is at his house and I can only work on it during the weekend. Thanks for your help
If I were to connect an AMP probe to BATT NEG cables, would I see the AMPs drawn from the pump?
You would only see the amp draw on the initial prime after the engine runs the voltage comes from the alternator so you won’t see it at the battery neg cable
Every time I watch one of your videos I learn something! Keep up the brilliant work Paul!
@spelunkerd Nice, I have never heard that quote. I like it too. The oil psi switch is simply there as a backup in case the relay fails. Of course the other side of that oil psi switch runs the oil psi gauge or light, so it serves two functions. I don't know why GM felt the need to backup the FP relay. No one else is doing that. Seems like a waste of copper wire to me. They must have had a lot of problems with this circuit early on?
does this car have a fuel regulator were is it
My 2001 Silverado, when cranking it will turn over "spinning good' Turn switch off restart cranking it will start the second, third or fourth try. when started it idles and run good, no problems until turning off and re starting. can it be the fuel pump?
Yes, do a psi check during cranking to confirm.
Love this video ! I have one question. Had a car in the other day and customer complained of long crank with his chev lumina. Did not get a fuel pump prime when key was turned on. noticed fuel pump wire dia was nearly the same as the car on this video.I noticed the red wire @ relay is the fuel prime. Where does that red wire get its power from ? didn't get much time to look at the car but gonna have to dive in Monday morning.thanks.
Watch my video on "fuel pump electrical circuits " it will answer your questions about this system
great teacher showing us how to think by deduction thanks a lot
@ScannerDanner That sounds a lot like a quote from Isaac Newton. It went like this, "If I have seen farther, it was by standing on the shoulders of giants...." I love that quote, and I love standing on shoulders, ha ha.
Why is that backup circuit from the oil pressure switch there?
@fivefortyeye540i Thank you, this one was a little tricky to film. There are so many different directions I could have taken this. Hopefully it was clear and not cluttered with too much info.
great stuff i see this nearly every day with the older cars were the earths play a huge part in things like this...
how much would a shop charge to fix that problem?
It was already at a few shops and they couldn't fix it.
If it was brought to me when I was in the field, it would have been an hour diagnostic time then another hour on the repair.
Garage rates are about $100 or so per hour.
You are awesome Paul. If i buy your e-book i'll have some kind of guide to learn how to diagnose problems like you did? I'm a begginer mechanic and current(and begginer) student of Electronic Engineering and i'm interested in learn this stuff. Thank you for your excellent videos!
@CoolasIce2 I just checked out that scope. It is an old analog scope. It will do want you want but you will have problems with "glitch" captures because there is no play back. I would recommend you go on ebay and buy a used Vantage (not pro, unless you can afford it)). It is a graphing multimeter and will get you by for awhile. Plus the data base in the tool is unmatched in this field. I have had students pick them up for around $200
I enjoyed this knowledge fully can I fly you to Vegas to troubleshoot my 1995 Buick century wagon at this point I’m atleast 80% sure it’s a wiring issue
The fuel pump was my most recent replacement and I’m thinking maybe same wiring problem all along was never the pump
Shoot I swapped my cat just to be safe
95? What engine? What is it doing? Do you have fuel pressure, injection pulse and spark?
I definitely have spark after watching this I am checking fuel pressure tomorrow it’s a 3100 odb1 and computer wont tell me anythingi have trouble with hard start once starts bogs and idles badly then if an drive a mile or so all seems well until next start usually
@spelunkerd Backing up the FP relay can't hurt. I'll take it. My '87 Cutlass Ciera has the same layout
What causes this?
Great Video and Thank you. But I have a question pls.
My 1994 Cadillac Fleetwood Brougham (LT1 engine) , runs without the Fuel Pump Relay plugged in, I demonstrated that for sure. But with the fuel pump Relay plugged in, my AC shuts off as I accelerate to 50 to 70 mpg, I did the fuel test while driving, and the fuel pressure never reached 41psi, the minimum specification for the fuel pressure. The fuel pressure hovered at about 34 to 35psi at low and high speeds. Could this problem be a ground issue, as you demonstrated with this video, or could this be a fuel pump problem that needs to be replaced. If you think this is a ground issue, where would I find the ground in the car that needs to fixed.
Thank you for your time and response.
+Sam Rafeedie If you are saying the fuel psi should be 41 psi at WOT and it is not increasing, then yes a poor power or ground to the pump can cause low psi but most likely you have a failing fuel pump.
ScannerDanner Ok so I have no clue if you will see this or not but my husband basically has a switch that turns on his fuel pump... It was like that when we got the truck. The other day on the way to work he went through a big puddle and his truck died. He found that the fuse in the switch was blown. It keeps blowing every time after running for about 10 mins. Usually if he hits a bump or is turning. It keeps on blowing. I know nothing about vehicles but wanted to ask if maybe you knew maybe what's going on. It says 15 a for the fuses we have been replacing. I don't understand why the fuse keeps blowing.
Brother, you keep out doing yourself. Amazing. God bless
Is that a fiat barchetta
Hi. I know this may not be related at all but felt maybe your knowledge could help me a little. My husband was driving to work the other day and drove through a puddle of water and his truck died. He has a switch that turns his fuel pump on. It was like that when we got the truck. Well he seen that the fuse in the switch was blown so he replaced it. It will run for about 10 minutes and then the fuse for the switch will blow again. It keeps blowing over and over. We tried replacing the switch to no avail. It keeps doing it. I don't know much about cars to begin with just thought maybe you might have an idea.
It is becoming more and more difficult to answer questions here. I have 80,000 people asking me for help now. So I have created a forum to help you guys better. It is free to join and we can exchange pictures, wiring diagrams and waveforms if needed to help guide you through the process of troubleshooting your vehicle. Thank you so much! Hope to see you there.
Paul Danner (ScannerDanner)
www.scannerdanner.com/forum/post-your-repair-questions-here.html