1998 GMC Jimmy Cuts out/stalls

SMOKEJOHNSON

MEMBER
1998 GMC JIMMY
6 CYL
4WD
AUTOMATIC
135,000 MILES

After 30 minutes of highway driving my motor starts to cut out, the max RPM that this happens at will steadily drop. If I pull over and shut the motor off it will run better for a few minutes before it starts happening again. Warmer outside temperatures seem to make the problem worst. I have found that if I ease into the throttle the RPM's will climb again but if I step on it the motor falls on it's face.

Here is a list of what I have tried so far:

air filter
fuel filter
throttle positioning sensor
mass air flow sensor
coil
ignition control module

I have also looked for vacuum leaks, I found none.

10 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Could be a weak fuel pump, or partially plugged exhaust that builds up and causes thelack of power. Try loosening the ehxaust before the cat converters(at bottom of manifolds) and driving it. It will be loud, but if the cats are the problem it will retain its power. As far as fuel goes, you will need a manual pressur egauge to verify whether or not it has good pressure. At your mileage it could very well need a new fuel pump

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Thursday, March 25th, 2010 AT 7:53 AM

SMOKEJOHNSON

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Thank you Jack, I will try the exhaust test before replacing the fuel pump. Do you think the need to drive it, for say at least 30 minutes on the highway, before the problems starts will hurt anything in the test?

On a side note on the fuel pump. When I turn the key to "run" without starting the motor my fuel pump starts running like they all do. The difference is mine never shuts off. It will keep running for over a minute. I think it should only run for a few seconds and then shut off. Maybe it is the fuel pump?

Some more interesting facts, all temperatures are Fahrenheit and all temperatures are outside air.

*30 degrees - Noticeable but not really a problem

*50 degrees - It becomes an issue but is still manageable by pulling over and turning the motor off. Works better if you sit for a minute but just killing it and starting immediately helps.

*70 degrees - I probably should not be driving it since the lack of acceleration becomes a safety issue.

Warmer temps are right around the corner and I am freaking out, LOL. Any and all help is appreciated.

James

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Thursday, March 25th, 2010 AT 12:59 PM

2CARPRO JACK

MECHANIC
11,533 POSTS

That is odd the pump runs that long. If you have afuel pressure gauge, see how fast the line pressure bleeds down, this is one indicator of a bad fuel pump. The ambient temp usually messes with the MAF sensor more than anything, but that is already off the list. By running it that long, you may at most set an o2 sensor code from the "ehxaust leak" that you creat to let the gasses out, maybe a "catalyst efficiency" code too. But they wont change the way it runs

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Thursday, March 25th, 2010 AT 5:31 PM

SMOKEJOHNSON

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6 POSTS

Thanks Jack. I will perform the exhaust test to see what happens. If that's not it I may just have to break down and pay a mechanic to check the fuel pressure/fuel pump. I will replace it myself but after checking the prices I want to know for sure before shelling out $300.

I'll let you know in a day or 2 what I find out.

James

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Thursday, March 25th, 2010 AT 7:22 PM

SMOKEJOHNSON

MEMBER
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Scratch 2 more things off the list. Created the exhaust leak this morning and took it for a test drive. Same problem occurs. While looking through my book I noticed a Intake Air Temperature sensor. Checked the resistance cold and then checked it again after the motor was warmed up and the resistance drops just like the book says it should.

Next on the list will be the fuel pump but like I said I think I am just going to have to pay a mechanic to check it out for me. Hopefully I can find someone to look at it this weekend.