1994 GMC Sierra Gradually decreasing power

KEITHSMOOT

MEMBER
1994 GMC SIERRA

Engine Performance problem
1994 GMC Sierra V8 Two Wheel Drive Automatic 206K miles

The truck would lose power initally with the "check engine" light on. Within 100 miles or less the power loss was more dramatic, to the point of barely able to move. I could pump the gas peddle and get some power, but not much. The engine seemed to idle nicely for a while, the cut off, especially at the end. The engine will turn over and start well. The truck sits most of the time, water in the gas? Electronic ignition module? Fuel pump? How do I test the (in-tank?) Fuel pump in my basement? Could I be completely off the mark? One note; the truck would run just fine at first, but when the "check engine" light would come on, the power loss would start. Waiting for the truck to cool down did not help.

5 Replies

MASTERTECHTIM

MECHANIC
4,750 POSTS

Keith lets start by jumping the a and b terminal of the diagnostic connector under drivers side of dash panel and then turn ignition on and count the flashes of the check engine light and get back to me, this will help a real lot in determining which direction to go.

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Wednesday, September 3rd, 2008 AT 7:53 PM

KEITHSMOOT

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4 POSTS

To Mastermechanictim,
I jumped A and B and counted three flashes of the check engine light. They were, one flash, brief pause, then two closely spaced flashes.
Thanks,
Keith

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Thursday, September 4th, 2008 AT 1:42 PM

KEITHSMOOT

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4 POSTS

I tried to jump the A and B terminals again. The 1-2 sequence repeated three times, then the check engine light flashed four times, paused then flashed four times, paused, four flashes, paused, ect. Is this what you were looking for?
Thank you,
Keith

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Saturday, September 6th, 2008 AT 7:06 PM

MASTERTECHTIM

MECHANIC
4,750 POSTS

Sorry for the long resoponse, a little vaca time. Your diagnostics is very good. Your problem I suspect is going to be one of 3 things but you can do all 3 things for about 50 bucks and I would recommend doing all 3. Code 13 and code 44 is what I gather you have and they are both related and are directly involved with the problem your having. Replace the fuel filter just to be safe. Replace the oxygen sensor. This is a one wire sensor on the exhaust y pipe and is most likely the cause of your problems but also on the thermostat housing on the intake manifold are 2 engine grounds for the computer, one should be tan and one black. I want you to clean the stud the grounds connect to and also lightly tug on the terminals to make sure the wires are not broken inside the insulation and replace the eye terminal if you need to. Im pretty sure this will solve your problem. The code 13 is o2 sensor fault and code 44 is lean exhaust mixture. Let me know

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Thursday, September 11th, 2008 AT 5:35 AM

KEITHSMOOT

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4 POSTS

Thank you for your ideas. Using additional sources I replaced the fuel pump and that appears to have done the trick. At least the truck will start now. The rain has prevented me from taking the truck out of my back yard, but things look better!
For some time the check engine light has come on and then gone off for no apparent reason. I will check the wires and sensors you suggest.
If the problem persists when I can drive the truck I will give you another call.
Thank you,
Keith