Fuel pump pressure?

Discussion in 'GMC Truck Forum' started by partsman, Mar 28, 2009.

  1. partsman

    partsman Full Member

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    So dealer fixed truck up, and so when I got home I checked it out again and all is well, but I had bought a fuel pressure tester and tried testing the pump pressuer, with Key on/eng off I got around 20-22 psi, with engine running I get 50Psi, now that does not seem to be what they say in the books, which if I recall was supposed to be 56-62Psi when key on/eng off, any idea if my pump is too weak?

    Or should I really worry about it?

    1996 GMC K250 4X4 219.000Km/137.000M 7.4/454 engine with auto trans.
     
  2. stumpuller454

    stumpuller454 Well-Known Member

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    the engine running isn`t so bad for psi, but the key on should be were its highest, are you able to drive with the gauge on? if you can go for a quick rip (with a buddy) and have him watch the gauge under WOT, should increase in pressure, but if it decreases it is getting weak...
     
  3. partsman

    partsman Full Member

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    It jumps up a bit when I pushed on the pedal, but did not go up too much more, hard to do by yourself.

    Will have to see if I could rig the thing up to stick out the side of the hood so I could see it when driving.
     
  4. crabtruck

    crabtruck Senior Member

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    Why would the pressure go up not down under WOT?
     
  5. partsman

    partsman Full Member

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    I should have mentioned if I push the relief button on the side of the guage while engine is running which lets fuel run into a container, it will run at a pressure of 30Psi,
     
  6. stumpuller454

    stumpuller454 Well-Known Member

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    Because of the pressure regulator, its controlled by vacuum, as vacuum decreases it raises fuel pressure for optimal injector performance....

    I`ve found driving my turck with the gauge on it generally raises pressure a couple of psi dunring WOT.
     
  7. leolkfrm

    leolkfrm Full Member

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    How did you make out with the bill?? did they cover it all?
     
  8. partsman

    partsman Full Member

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    Things turned out to my advantage, so I was glad, and of course there is a guarantee on any work they did.

    Now as for the fuel pump, apparently the pressure at key on/Eng off is to be taken right at the turn of the key, not after like I did, so will have to have someone hit the key while I can watch the pressure, apparently it will hit what ever the pressure is supposed to be then drop down to residual pressure, so have to redo it.
     
  9. partsman

    partsman Full Member

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    Well got the 12 year old daughter to hit the key, and with key on and engine off the pressure goes right up to 58Psi, so I would say I am good to go.

    Of course I don't imagine that tells how long the pump will last, but to me it means it is a strong pump at this time.
     
  10. stumpuller454

    stumpuller454 Well-Known Member

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    Good to hear! may it last for years!....hopefully i didn`t jinx it!
     

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