Fuel pressure test result today

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by bazar01, Sep 15, 2012.

  1. bazar01

    bazar01 Rockstar 100 Posts

    I finally got a chance to buy a fuel pressure tester today.

    Here are the readings on my 2001 Suburban.

    1. With the engine off, gauge connected to fuel line, 0 psi.

    2. With engine off, ignition switch to ON, fuel pump ran for a few seconds, pressure rose from 0 to 45 psi. Then fuel pump stopped, pressure dropped to 15 psi in less than 1 minute. Then to 10 psi after 2 minutes.

    3. Turn engine ON, with engine idling, fuel pressure rose to 44 psi.

    4. Turned engine OFF, pressure dropped to 15 psi in less than 1 minute and 10 psi after 2 minutes.

    How is my fuel pump?

    Last edited: Sep 15, 2012
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Someone would have to confirm specs for your engine (can I assume this is your 2001 5.3)? My '98 fuel system runs at 60-66 psi. If your engine is supposed to run in that same range, it would appear that your fuel system is either running low, or your fuel pressure gauge is reading low.

    Low fuel pressure can be caused by more than just a weak pump. A failing pressure regulator or a clogged filter would also show up as low pressure. The pressure bleeding off like it does indicates a leak of some kind, or an injector stuck open, or a bad check valve in the pump.
  3. bazar01

    bazar01 Rockstar 100 Posts


    It confirms my suspicion too. Either a bad check valve or a stuck open injector.

    is the check valve on the pump inside the tank?

    What is the best way to check a leaky injector?

    Yeah, i agree, the 44 psi pressure is a little low. It runs fine though. It only takes two tries to start.

  4. bazar01

    bazar01 Rockstar 100 Posts

    I checked the 2011 Silverado with 5.3 a few minutes ago.

    I turned the ignition ON, engine OFF, fuel pressure went up to 55 psi.

    I turned the ignition OFF, fuel pressure never dropped. It stayed at 55 psi.

    Now, which one should I do first?

    Do I do the fuel pump replacement, then check fuel pressure? If the fuel pressure holds, I am good to go. Then if the fuel pressure drops, then I have to chase the leaky injector?

    Is it fairly easy to pull the fuel rail, put small glass jars on each injector, turn ignition ON, and check which injector leaks?

    I appreciate the advise. Thanks.
  5. bazar01

    bazar01 Rockstar 100 Posts

    Well it make s more sense to pull the injectors out and check which one is possibly stuck open and causing the fuel pressure to drop to 10 psi.

    I decided to take a look at the fuel rail. Only two 9mm hex head bolts securing the rail on each side. Why not do this first.

    The fuel rails pulled up with a little resistance but they pulled up.

    Hook up pressure tester. turn ignition ON, fuel pressure rises to 45 psi, then it slowly dropped. Inspected all the 8 injectors and they were all dry.

    Ohh s^$t, it must be a leaky check valve on the fuel pump.

    It still drives fine but i had an incident this past weekend where it started missing and wont accelerate past 55 mph. Initially i thought it was the a/c compressor locking up, because i was able to get it back home with no issues with the a/c off. It has been driving fine with the a/c off but i do not want to change out the compressor without making sure it was the problem.

    Now I am very sure the fuel pump is getting weak.

    I will drive it around town until the gas tank gets low and I will replace the fuel pump.
  6. Boonduff

    Boonduff Rockstar 4 Years 100 Posts

    Sounds more like a pressure regulator to me.
  7. bazar01

    bazar01 Rockstar 100 Posts

    I never thought of that. If it is, a lot easier than dropping the tank to change the fuel pump. You are right. I forgot about the pressure regulator having to bleed off fuel to regulate the pressure in the rail. Is it possible the bleed valve is open?

    You got me thinking now.

    How do I block off the return line so I can do another fuel pressure test to check if it holds pressure?
    Last edited: Sep 16, 2012
  8. bazar01

    bazar01 Rockstar 100 Posts

    Anybody that can recommend how to block off the fuel return line from the regulator? I hate changing parts without actually knowing it is bad.

    There is a clip on the return line connection from the rail. I will try to unclip and separate the lines. Then from there I can probably find a way to cap the return line and perform another fuel pressure test. If the pressure holds, then I know it is bad.

    How about just pinching the return line with a vice grip or something?

  9. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    Fuel pressure for the 99 to 06 5.3 gas only engine should be 55 to 62 PSI with ignition on and engine off. I do not see a need to block of the return line but to only remove it and see if anything is returning to tank. If it is returning anything and the pressure is less than 55 then I would replace regulator, if not, then the pump is at issue.
  10. bazar01

    bazar01 Rockstar 100 Posts

    But isn't it that there will be fuel coming out of the return line no matter what with engine OFF or ON. Excess fuel has to come out to maintain set pressure. Isn't it that the fuel pump has more volumetric capacity than what the engine needs, that's why there is a return line and that's why I wanted to block it off and see if the pressure rises to 55 psi and holds, but I could be wrong.

    I will try this when I get home tonight.
    Hook up pressure tester, open the return line, attach a hose from return line to a container to catch fuel, engine off, turn ignition switch to ON, let it pressurize and watch if fuel comes out of return line and indicate fuel pressure. Watch return line for fuel while pressure dropping.
    Then do a second test with return line blocked off and see if pressure holds.


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