00 Denali Misfiring after MFI spider upgrade

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by TurboGSR96, May 29, 2011.

  1. TurboGSR96

    TurboGSR96 New Member

    *just noticed I posted in wrong section, excuse my mistake* Whats up fella's I have a 00 Denail 178k on the clock I am the original owner. I have been at battle with the random misfire code (forget exact code and cyl) but its the same code everyone blows after a while. I have replaced the Cap, Coil, Rotor, Plugs, Wires and Fuel Filter and replaced a faulty O2 about 8k miles ago and the truck would still heavily misfire once you got a good load on it, sometimes so bad it would feel like the motor is going to break free from the mounts and drop out the bottom! lol

    So today I replaced the stock spider assembly with the Delphi MFI unit, replaced all the gaskets with a Fel-Pro Kit, reassembled fired the truck up and took it for a test drive and its still doing the same damn thing. I didnt unhook the battery so I did that thinking maybe it needs to reset and it got a little better but still misfires under mid/high load and when going into overdrive.

    With all of that being said, my fuel pump is louder than the 2 external inline Walbro 255hp's I have on my race car.... assuming I should replace the pump next? Does anyone know what the fuel pressure should be on the truck and do I check it running or with just the key on?

    If the pump doesnt fix it I am yanking the motor, swapping in a Cummins and going emissions exempt screw this :glasses:

    Thanks in advance.
    Last edited: May 29, 2011
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    You will want to test the Fuel Pressure.. and it should be in the 60-66PSI with the key on.. and no exceed 75PSI with the motor running. also what other codes are you getting because the Distributors in those trucks are notorious for going bad as well..
  3. TurboGSR96

    TurboGSR96 New Member

    I had to run hard to get it to blow the code, P0306 Cyl 6 Misfire... same code its been blowing for a long time. I did check the fuel pressure last year and I know it was under 60psi key on or running, but that was before I replaced the Reg/Spiders. I will check it again this week thx for your reply.

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