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Pete
Pete, GMC Technician
Category: GM
Satisfied Customers: 16138
Experience:  14 years GM dealership technician and training.
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1995 gmc: 1 ton van with 7.4 liter..starts right..revs

Customer Question

1995 gmc 1 ton van with 7.4 liter. Engine starts right up when it's cold and idles fine. When you give it gas it stumbles badly and then revs ok. When warmed up it won't restart. I've already changed cap, rotor, ignition module, coil and spark plugs. Spark blogs were black. Tested map sensor. 4.7 volts when not running, 1.4 while running. No trouble codes in system. Fuel injectors are spraying fine it seems (visual test).
Submitted: 3 years ago.
Category: GM
Expert:  Pete replied 3 years ago.
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.

Hi.

I just need a little more info to assist better.

Has fuel pressure been tested at all?

Has the fuel filter been replaced in the last year or 15,000 miles?

Does this vehicle have the electric egr valve or the vacuum controlled egr valve and if it has the vacuum if you unplug the vacuum hose from the egr valve and then see if it revs up normally is it o.k. then?

Let me know so we can continue,Thanks Pete!
Customer: replied 3 years ago.
Thanks for helping.
Fuel pressure hasn't been tested. I wanted to, but I don't know how. Fuel filter hasn't been changed in a while, not sure how many miles. Egr valve is electronic. Van currently won't start. I just pulled a plug to see how it looks and the brand new one's are black (not wet) after maybe 20 total minutes of idling time. Thanks, Rob
Expert:  Pete replied 3 years ago.
I apologize for the delay.

The fuel pressure test is done with an adapter in line where the fuel filter is located and then a fuel pressure test gage can be installed onto the adapter.You might be able to purchase or borrow this tool from a parts store if not then a dealer or shop will have to do this testing for you.Your fuel pressure should be between 26 and 32 psi.If it is lower then this then you may have a faulty fuel pump or a plugged fuel filter.

It sounds like you are running rich here,try holding your foot to the floor on the gas pedal while cranking over the engine and see if it starts then.This is a clear flood mode which will shut off the fuel to clear out any remaining fuel.

Do you see fuel coming out of the injectors now while cranking with your foot off the gas pedal?

Do you have spark on any or all plug wires (you can use a spark tester or timing light to check for spark)?

Let me know what you come up with here,Thanks Pete!
Pete, GMC Technician
Category: GM
Satisfied Customers: 16138
Experience: 14 years GM dealership technician and training.
Pete and 7 other GM Specialists are ready to help you
Customer: replied 3 years ago.
Thanks for your help on this. It was the coolant temp sensor. I unhooked it and it ran normal again. I think it was probably sending a cold reading and the engine was staying in a choked type state. Also why it didn't trigger an error code.
Expert:  Pete replied 3 years ago.
I was heading in this direction as the plugs were black,this wont set a fault code as the computer will think the engine is actually that cold and causes this problem.

On the newer vehicles this would most likely set a fault code but on this older vehicle it usually wont.

Let me know if you need anything else in the future.

Thanks Pete!

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