Question about 2001 GMC Jimmy

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No fuel to the engine

I just replaced the fuel pump in a 1994 GMC jimmy. Now the engine does not get fuel. I disconnected the line at the back of the engine and the fuel runs out, but the engine itself is dry. If I put gas in the throttle body the engine will run for a few seconds then dye. What I should I try next?

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  • 5 more comments 
  • jas0n_gall Nov 08, 2008

    Is there a way to check the oil pressure switch, or bypass it to see if thats the problem?

  • jas0n_gall Nov 08, 2008

    its a 4.3. The story I'm getting from the owner (who replaced the fuel pump) is that it sounded like it was going to dye when it was idling in gear. He replaced the pump and now has this problem. If I bypass this switch will there be any residual effects to the engine?

  • jas0n_gall Nov 08, 2008

    got it. But when I turn the key on I can hear the fuel pump run for a few seconds. When I attempt to start the truck the oil pressure reading on the gage shows about 40 PSI. Doesn't this eliminate both the fuel pump and the relay? I am getting spark (grounded a plug against the block) and fuel at the pressure port where the lines connect to the intake. But thats where the fuel seems to stop. When I look thru the throttle body it looks dry as a bone. Unfortunatley, the fuel rails on this truck are internal to the intake manifold. Do I have any option but to pull the intake manifold to check for power to the injectors? or to see if they are clogged?

  • jas0n_gall Nov 08, 2008

    I am also in the process of replacing most of the vacuum lines. Many of the are torn/dry rotted. Could this be the issues as well?

  • jas0n_gall Nov 08, 2008

    vacuum lines are replaced...still no go.

  • jas0n_gall Nov 08, 2008

    heres the latest. When I cover the throttle body with my hand and turn it over the engine will start and run (not very good, but it does run). I am getting around 35-40 PSI of fuel pressure at the test port on the back of the motor and the spark is strong. That eliminates the oil pressure sensor, since it will run with the airflow cutoff. Anymore help you can give sure would help!



  • jas0n_gall Nov 09, 2008

    i turned out to be the sensor located on the throttle body (not the TPS) not sure what it is but when I disconnected it, it started right up. Thanks for all your help, I fixed alot of others on this truck using the info you gave me.

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'puter wont deliver fuel if oil pressure switch is reading bad weak or faulty..or if ignition is not sending proper signal to 'puter....on the mechanical side...you could have a bad fuel pressure regulator sending all fuel right back the return line and not into the engine/ clogged fuel rail due to using some sort of nasty fule injector cleaner than turned the lines to jello inside..etc .etc.

Posted on Nov 08, 2008

  • 3 more comments 
  • milespeed Nov 08, 2008

    yes..lets see..94 ..5.7 motor yes?..pressure switch is behind distributor..center back 'tween firewall and center of motor..bulbous..connector there needs jumpered...not sure which 2 of those 3 wires ..need to step out a while .sorry ..look on internet for switch bypass procedure or i will find and share when i return .. be well, miles

  • milespeed Nov 08, 2008

    ok , lets backtrack some ....basic engine needs..air fuel spark..and timing set so they work optimally..
    if we tell computer oil pressure is ok (bypass) and it runs..we should shut it down fast and find out why it has low oil pressure or if switch is bad ...capiche?.....common thing here is .. ..running engine but seems to idle low..replaced otherwise working fuel pump and no run condition now...doesn't it stand to reason that the new fuel pump or its associated replacement (hoses,wiring) is at fault here?.... you said the motor runs when you spray into throttle body with carb cleaner or similar? it should continue to ruin if oil pressure is 4psi or greater..it should continue to run if it gets trigger signal ..(crank sensor)...and ECM (computer) is healthy

  • milespeed Nov 08, 2008

    and lastly ..fuel pump relay..must check...

  • milespeed Nov 08, 2008

    air leak..., making fuel air mix wrong...major vacuum areas to check are rip in throttle body to air cleaner causing mass air sensor values to be way off..spray carb cleaner around as you run motor with snorkle blocked so it runs and when RPM changes you are close to source of vacuum leak :)...be sure to spray near intake manifold/// cylinder head mounting areas for leaks as well....let me know

  • milespeed Nov 10, 2008

    Y V W

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