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1990 Pontiac Firebird Question: Replaced Fuel Pump on 1989 Firebird

 

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D Birdman, 5.0L V8, San Jose, CA, January 11, 2011, 23:46
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I had the fuel pump replaced on my firebird, ran good before pump replacement. Now experiencing major engine stumble and backfiring with new fuel pump. I suspect impurities in fuel line. I'm getting approx 35 psi at fuel distributor which is ok. Need help!! Thanks.

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  • Answer #1

    DaveJHM January 12, 2011, 00:40
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     Master

    Did you replace the fuel filter?
    Also, can you verify the quality of the new pump? I'm showing you should get in the 40's in fuel pressure.

    Last, backfiring and stumble can definitely be caused by an air intake leak. Check your vacuum lines, intake gaskets, air box and tube.

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    D Birdman, January 12, 2011, 22:59
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    Thanks Dave, I'll check it out.!!

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  • Answer #2

    mastertech6371 January 12, 2011, 07:18
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     Master

    I agree with Dave. get it re checked. Did you replace the fuel filter as well??

    Roy

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    D Birdman, January 12, 2011, 23:04
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    I replaced the fuel filter 1 month before the fuel pump went out. I think it's possible that it could be clogged as a result of the gas tank being removed and replaced. This is a new experience for me. This helps. Thanks for your feedback!!

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  • Answer #3

    ZeeTech January 12, 2011, 07:43
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     Master

    35 psi seems to be low, unless it's the regulated pressure.
    Here are the factory specs:
    Ignition ON Engine OFF 40.5 to 47.0 psi
    With Regulator Vacuum Applied 3.0 - 10.0 psi Less than Ignition ON Engine OFF
    Beside the pressure, the volume is an important factor. The fuel pump should supply 1/2 pint or more of fuel in 15 seconds.
    I guess you have the MPI (multi port fuel injectors) instead of the TBI. Are you sure you get the fuel pump for the MPI?
    The fuel pump's part# for the MPI: 25116163 (the 8th digit of the VIN is F) meanwhile the TBI fuel pump's part# 25168719 (8th digit is E)

    Zee

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    D Birdman, January 12, 2011, 23:24
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    You're guess is right, I have MPI. I'll backtrack and check. I hope my mechanic knows the difference between the "E" and "F" fuel pump because it's a hell of a lot work and expense to get to the fuel pump. BTW the repair manual for the '89 Firebird calls for 34-39 PSI (ref pg 309 chap 13). Thanks for your feedback!!

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    ZeeTech, January 13, 2011, 04:36
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     Master

    Yes, 34-39 psi is correct, if it's the REGULATED pressure, with the vacuum hose connected to the fuel pressure regulator. According to the specs 30,5 is the minimum regulated pressure.
    Do you know if the pressure was measured with the regulator connected?

    Zee

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