QuestionHope you can advise. Its a 94 GMC G2500 conv van with 180m miles. 350 engine. Ran well but seemed boggy. Driving at 30mph, faint backfire type noise (thump sound) Van died and would not restart but seemed to crank ok.
Changed fuel filter, then fuel pump (napa brand)
Van would start & run one time. Then would only crank another. No apparent relation to hot or cold engine. It would not start one time, then not the next time.
We changed the fuel relay, oil pressure switch
Additionally, we changed the distributor cap & rotor which was in need of changing (some burn marks)Fuse not blown.
We were also told to replace the fuel pump wiring harness.
But cannot find any voltage on one of the wires to the fuel pump.
The tank is not now strapped back in place.
I will take it to a shop when I can afford to
but Im hoping you have some suggestions before
I do.
Thanks, Mel
AnswerYou stated: Im hoping you have some suggestions before
I do.
response: Here is HOW the fuel pump circuit works on your van.
When you initially turn ON the ignition switch to start the engine, The fuel pump receives battery voltage from the vehicles computer to the FUEL PUMP RELAY of which energizes and sends battery voltage back to the fuel pump for ONLY 2 (TWO) seconds.
This 2 second run period pressurizes the fuel system in order for the vehicle to start.
Once the vehicle starts the FUEL PUMP RELAY is BY-PASSED and the
Once the vehicle starts, The battery voltage from the vehicles computer is sent to the oil pressure switch of which closes the internal contacts of the oil pressure switch due to the oil pressure from the running engine and sends the battery voltage back to the fuel pump of which will now run constantly as long as you have oil pressure.
On SOME models, The oil pressure switch is NOT used in this manner and the battery voltage is sent directly from the vehicles computer back to the fuel pump as long as the engine is running due to various sensor inputs sent back to the computer.
If you look near the fuel pump relay usually tied to the fuel pump electrical harness is a single wire that has a plastic connector with a female insert.
This single wire is your TEST POINT for diagnosing a fuel pump operation fault.
What you can do is to use a 10 AMP FUSED jumper wire and put battery voltage to this connector from the battery itself. This will cause the fuel pump to run all the time as long as the 10 AMP FUSED jumper wire remains installed in this manner.
Do NOT EVER use a plain piece of wire as a jumper wire for this test as if their is a short in the fuel pump circuit you can destroy the vehicles computer system. Thus the reason for the FUSED jumper wire.
WHEW, Let me know.
I do not have a staff of people helping me answer your questions, I do it all by myself, except some typing help from my wife or son as the old fingers just don't flex as well as they used to. Therefore, Due to being retired and an OLD computer, That is so old it does not even have SPELL CHECKER on it and being on a dial-up connection, Please excuse the TYPO'S.
I do my best to respond to questions within 4 to 5 hours, But due to the volume of questions I receive on a daily basis I answer them ASAP. If you require a faster response you can e-mail me directly at the below e-mail address as I check it more frequently.:
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Sometimes when you have to replace a part, I will ask you if I can have the old part, As my son and I rebuild them and sell them for extra income. I will pay the shipping costs as long as it does not exceed $10.00.
There are also times that you have some written information that you just don't understand or need help with it, You can e-mail it to me at the above siad e-mail address or you can fax it to me, But contact me FIRST at the e-mail address and I will give you my fax #. However, Again due to my OLD computer I have to log off from the dial up service in order to receive any faxes on my seperate fax machine.
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