Question about 1999 GMC Suburban

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I have a 99 suburban that has 203,000 miles. It has developed a problem of taking a while to start. I have replaced fuel pump twice, the latest was about 3-4 years back. I have not checked pressures but fuel pump does run and then cut off when starting up. It will start well after I shut it off and restart. It has no problem accelerating after it starts( seems to be getting plenty of fuel). It does seem that it coast an unusually long time when letting off the gas. I also get a slight flutter in fuel gauge but it has done that for the last 6 years. I did install fuel filter recently but it did not help. Any suggestions.Fuel pressure regulator? IAC?

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  • ritchie_luke Jul 16, 2009

    Thanks for responding. Cycling the key seemed to have no effect. It is usually just a little slow after a few hours but is always slow after sitting overnight it takes about 4 tries to get it to start. It is a 1/2tn,5.7, 2WD.

  • ritchie_luke Jul 16, 2009

    I pulled out my gauge and it was not working. I will get a new one this evening. It sounds like the static pressure should be 60-66. I did also read that it should jump up by 10psi by shutting off the return. Not sure what the best way to accomplish that is? Pinching the hose? Also read something about pulling vacuum line on the pressure regulator and pressure should go up by 10psi. Sound correct? Any other suggestions of how/what I should check? Thanks for the assistance!

  • ritchie_luke Jul 21, 2009

    Fuel pressure does drop,
    I did replace the fuel pressure regulator as it was not that expensive.(a little more work than I wanted but not too bad). This did not help so after putting a gauge on it, I did see that when first turning the key on, the pressure would build to 50-55( 1 or 2 times hit 60). It would then start dropping. It would take about 5-8 seconds to get down to 0 psi. From there I decided to change out the fuel pump. It now reaches 62 at static(consistently), but it does seem to drop off at the same rate as the 1st pump. It is starting correctly for now but I have only started it a few times and it is too early to celebrate. I will know more if it continues to start well for a couple of days. Could the dropping off of the pressure be normal for this vehicle? Thanks for your continued assistance! I will let you know what happens.

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  • GMC Master
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I believe you have a fuel regulator weak or dirty injectors.
Try turning the key to the "on" position ( do not try and start) wait until fuel pump stops running (3-5 seconds or so ), turn the key off and immediatly repeat for 3 cycles. On the 4th key rotation, start the vehicle. Does it seem to start up faster?
If so, the regulator is weak, however, the fuel pump does have a check valve in it to prevent fuel from leaking back into the pump and maintain line pressure.
Try the diagnostic proceedure above first and we can go from there.
Good luck, let me know.
Regards,

Posted on Jul 15, 2009

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  • Bruce Bracey
    Bruce Bracey Jul 16, 2009

    A fuel pressure gauge would be the best way to test the fuel system to determin if you have the correct fuel pressure.

    With that many miles it would be very helpful to have the injectors cleaned. It would improve starting as well as fuel economy. Dirty injectors do not atomize fuel properly and can cause hesitations, hard starts.

    I use the Cheveron Fuel system cleaner. It is a bit more expensive than some of the others but is very concentrated and cleans injectors, intake valves and combustion chambers very well. You might want to run two or three tank fulls back to back. Its worth the effort.

    Good luck,

    Regards,

  • Bruce Bracey
    Bruce Bracey Jul 16, 2009

    You are correct, 54 to 60 PSI and an increase of 10 + PSI when you pinch the return line off. If all that checks OK, stop the engine and watch the pressure, it should not fall more than 10 PSI. If it drops to 0, you may have a leaking pressure regulator or fuel pump check valve.

    We can cross that bridge when we get to it.

    Let me know.

    Regards,

  • Bruce Bracey
    Bruce Bracey Jul 21, 2009

    No, it should not drop off to "0" psi. If both the pump and regulator have been changed and it is leaking down, the only other component that would cause that is one or more injectors. Dirty injectors will not seat and seal properly and allow fuel to leak into the cylinder.

    As I had stated before, you might want to run a couple of tanks full with the Chevron fuel system cleaner. It will clean the carbon that is absorbing the fuel at start-up and will help the injector leaking issue.

    Good luck, let me know.

    Regards,

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