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  1. #21

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    Palmer_df0130, Did the new fuel pump solve the FPR buzzing problem? I was not clear if that was the solution for you, or if it was the FPR replacement. I checked my fuel pressure and key on w/engine off the pressure is 52. I've had a hard time finding consistent specs on what the 99 Silverado 5.3 should be. Some say key on w/engine off should be 55-62 psi, engine running it will drop 5-7 psi and heard that is normal. My fuel pressure is 52 psi with the engine off, 47 when it's running. So the drop is in line with the 5-7psi, but it's the 52 psi that concerns me. It seems low but I'm not positive. If it was within the specs, it seems that it should go from 62 engine off to 55 with it running, or at the lowest from 55 to 48. You said in your post that Delphi said the fpr buzzing was due to a fuel pressure problem. What was your fuel pressure before the new pump? I'm considering replacing the pump with a new AC Delco just to see if the buzzing disappears. If that doesn't solve it, I'll have to try the fuel rails. Also, my FPR is a brand new AC Delco. Any recommendations based on what you learned? Thanks.
    Last edited by Scottg; 10-19-2013 at 02:20 PM.

  2. #22
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    the 5.3L engine the fuel pressures ignition on engine off are 60 psi area...and it should shoot up fast and hold. engine on the pressure should drop down to 53-57 psi. then you remove the vacuum line to regulator and the pressure should rise to 60 psi. if this is what you get the pump is good...if you get lower pressures then the pump is bad.


    with pressure drop off with key on eng off it may mean the pump/injectors/regulator is bad. this is where you must measure pressure at the filter. this is where the pressure should be like 75 psi and hold...

    I have a gauge that has a drain valve port. when you do this test this is needed so that you do not get fuel showered ....

  3. Thanks Scottg thanked for this post
  4. #23

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    That is exactly what I needed to know. Based on those specs my pump is bad so I will replace it. Will reply with the results once the new pump is in. Thanks for your help.

  5. #24

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    Glad to know people are able to find these posts and is helping them as they diagnose their issues.

    Steve
    10 Chevy Traverse LT AWD
    02 Chevy Trailblazer LS (110K+ miles - loaded except for 4WD - WRECKED!)
    99 Chevy Cavalier LS (105K+ miles - commuter car)
    78 Chevy Suburban Silverado (454, 3/4 ton)
    62 GMC 3/4 ton Pickup (350 police interceptor)

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  6. #25

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    I installed a new AC Delco fuel pump and it solved the problem. Fuel pressure is now at 60 psi engine off key on. Drops to 58 when the truck is running, as you specified. And the fuel pressure regulator is no longer making the buzzing noise. Thanks again for your help, I appreciate it.

  7. #26
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    Quote Originally Posted by Scottg View Post
    I installed a new AC Delco fuel pump and it solved the problem. Fuel pressure is now at 60 psi engine off key on. Drops to 58 when the truck is running, as you specified. And the fuel pressure regulator is no longer making the buzzing noise. Thanks again for your help, I appreciate it.
    as the fuel pump gets older the engine on pressures will drop slowly .It is good that after you replaced the pump you now know what good pressure is and how the engine is running.

    my 2000 OEM pump is around 55 psi ...13 years plus old. keep the fuel level above the 1/4 mark to protect pump from damage...it will overheat and then the windings get damaged.\ with less than 1/4 tank..

  8. #27

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    Hey guys, Last week I replaced the fuel pump on the truck and then a couple days later the fuel pressure regulator (both Delphi OEM parts).

    Prior to the FPR replacement, I had ZERO vibrations on the return line. After replacing the FPR I get crazy vibrations in cold weather until the the truck is warmed up. BTW my truck is an 02.

    To the guy who replaced his rails, could you shake the rail and here movement inside?

    In the mean time, I have a replacement FPR on the way

  9. #28

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    Update: Unfortunately the FPR buzzing has returned when it's cold outside (approx below 50F). Just like akcooper9 stated, I have also replaced the fuel pump with an AC Delco, and the FPR three times. I thought that after replacing the fuel pump and the buzzing went away, the problem seemed to be fixed. But it was likely due to a littler warmer weather that made me think this. Once the cold weather returned (I'm in MN), the buzzing is back.
    I picked up another GM FPR from the dealer after speaking with a local mechanic; he felt it's possible I have gotten two bad FPRs. Seemed unlikely but I replaced it again, but the buzzing continues. I tested the manifold vacuum pressure on the line that attaches to the FPR. It's holds at a steady 19" Hg which I think is good. Can anyone confirm if that is the factory pressure this vacuum reline should be at? Truck runs great, no issues starting or running. Fuel pressure is good. I'm at a loss to what is causing this. No mechanics I have spoken with think it's the fuel rail. One stated "That's new to me..." because he said he's never had to change a fuel rail because of this problem. I'm still considering it. In summary, I have installed a new AC Delco fuel pump, new fuel filter, and 3 new GM FPRs. The only thing I have not replaced is the fuel rails and fuel line. Any additional thoughts are appreciated!

  10. #29
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    Quote Originally Posted by Scottg View Post
    Update: Unfortunately the FPR buzzing has returned when it's cold outside (approx below 50F). Just like akcooper9 stated, I have also replaced the fuel pump with an AC Delco, and the FPR three times. I thought that after replacing the fuel pump and the buzzing went away, the problem seemed to be fixed. But it was likely due to a littler warmer weather that made me think this. Once the cold weather returned (I'm in MN), the buzzing is back.
    I picked up another GM FPR from the dealer after speaking with a local mechanic; he felt it's possible I have gotten two bad FPRs. Seemed unlikely but I replaced it again, but the buzzing continues. I tested the manifold vacuum pressure on the line that attaches to the FPR. It's holds at a steady 19" Hg which I think is good. Can anyone confirm if that is the factory pressure this vacuum reline should be at? Truck runs great, no issues starting or running. Fuel pressure is good. I'm at a loss to what is causing this. No mechanics I have spoken with think it's the fuel rail. One stated "That's new to me..." because he said he's never had to change a fuel rail because of this problem. I'm still considering it. In summary, I have installed a new AC Delco fuel pump, new fuel filter, and 3 new GM FPRs. The only thing I have not replaced is the fuel rails and fuel line. Any additional thoughts are appreciated!
    you may have to replace the fuel rail. most likely a piece is loose inside of it.

    the vac is that of the engine manifold. that 19 inches is a good normal reading @ idle. when you rev engine it should rapidly drop and then rise. when you let off the throttle the vac should rise to 21 or more then come down to the 19 .

    when you floor it the vac drops and the fuel pressure rises. let off the pedal then you get highest vac and the lowest fuel pressure.

    fuel rail noise is not common ..

  11. #30

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    Thanks for the quick response, I appreciate it. I will replace the fuel rail and reply with the results.

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