Question about 1998 GMC Jimmy

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Fuel not getting to cylinders...pump, regualator, other?

I replaced a dead fuel pump two months ago on my 1998 GMC Jimmy. For the last month or so, I got some 'random misfires' according to the engine code, the vehicle kept running when it happened. A few weeks ago I replaced the fuel filter to see if that would help; it didn't. Currently, it won't start. Fuel is not getting to the cylinders. I am getting 30 psi of pressure with the key in the 'on' position, it very slowly goes down to about 28 psi...(over 30-40 seconds).

I have read on here that while plugging the return line you can check the pump pressure. However, when I removed the return line from just behind the throttle body, no fuel came out to block.

Bad fuel pump/assembly? Bad regulator? Both repairs will consume time and money...I'd like to be more certain of the problem before I start moving a wrench. Ideas/help?

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  • robcurtiss3 May 09, 2009

    It was a store brand from Advance Auto Parts...looks like "Airtex" is the brand name...replaced it on April Fools Day.



    Is it common for a fuel pump to put out some pressure but not enough? I would think an electric fuel pump is either working or broken.

  • robcurtiss3 May 10, 2009

    It seems a faulty regulator would cause a 'quick leakdown'...that I definitely do not have. Sounds like tomorrow will be a day to replace a fuel pump...at least all the bolts have been recently loosened! The pump is under warranty, but I will try to upgrade to the Bosch unit they have if I can.



    Thank you for your insight.

  • robcurtiss3 May 10, 2009

    I replaced the enitre pump module and plan on doing so again tomorrow. I haven't found any leaks in my gas line nor any drop in pressure once the pressure hits 30 psi...



    What is the best way to cap the return line? i pulled the return line from the intake manifold and nothing came out when the ignition was turned on...

  • robcurtiss3 May 10, 2009

    It was the fuel pump..was able to get it done in just over 2 hours and it fired right up. Now to hope this one lasts longer than 5 weeks!

  • Anonymous May 12, 2009

    ddddd

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  • Master
  • 585 Answers

The pump should be capable of at least 60 psi with the return capped. I seriously doubt that the pump is at fault. I fought with this myself once going through three pumps before I found the leak in the flexible line in the tank that goes from pump to metal line.

Posted on May 10, 2009

  • Bruce Volkers
    Bruce Volkers May 10, 2009

    You got nothing to pass rhe pressure regulator because it typically takes about 45 psi to overcome it. You might want to check to see that there is a full 12-vollts at the pump. A voltage drop somewhere could explain the low pressure. If the voltage is low, find and correct the cause. If the voltage is correct, replace the module.

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  • Master
  • 678 Answers

30psi seems pretty low, should be around 45 or so. It sounds like your fuel pump is done again. What did you replace the pump with, OEM or a parts store part?

Posted on May 09, 2009

  • Christopher Foulkes May 09, 2009

    I've seen it on a few occasions. GM used "poppet" injectors on a lot of their trucks. These injectors require a certain fuel pressure to open. A few pounds too low and the injectors won't open causing a no start condition. Quick google search brought up this article, worth a read.http://www.babcox.com/editorial/us/us300...

    I would bring back the bad autoparts store pump and purchase an oem replacement from a GM wholesale site like gmpartshouse.com. Unfortunately it looks like it cost about $350 for the fuel module but atleast it will last for more then a month.




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