99 5.7 Vortec - what is fuel pressure spec after MFI upgrade

Discussion in 'GM Powertrain' started by triple-4x4, Jun 1, 2010.

  1. triple-4x4

    triple-4x4 New Member

    I changed the fuel injector assembly from the stock CSFI to MFI about 30k miles ago. Now when I check fuel pressure, I read 55 lbs. Does anyone know what the correct spec for fuel pressure should be after you do the MFI upgrade on a 99my 5.7L Vortec?

    I am trying to track down a problem I believe to be engine related. It seems to buck & surge while I drive, almost like uneven cylinder firing.

    99MY K1500 Suburban, 5.7L, 200k miles.
  2. triple-4x4

    triple-4x4 New Member

    I checked the mechanical timing again

    After replacing the distributor and not finding any difference in the way the truck runs, I took it apart to double check the timing. Everything lines up - at #1 TDC ( I tested by taking out the plug & feeling compression ) I had the distributor lines up to the correct mark, just like it shows in the factory service manual. Do I need a scan tool to check the timing?

    I have had the battery disconnected. Does this cause the Engine PCM to forget any learned timing offset?

    Still haven't found the fuel pressure spec for MFI. Next I will change the fuel filter because it is due again anyway.
  3. badapple88

    badapple88 New Member

    hey there, I am having the same problem after replacing my scfi to mfi. Was wondering how or if you resolved your problem. I smell half burned gas as well and getting poor fuel consumption.
    thanks in advance
  4. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    The fuel pressure for the 99 to 2006 V8 is 55 to 62psi for reg gas engine. this is for Sequential Fuel Injection SFI. What upgrade is available?
  5. Boonduff

    Boonduff Rockstar 4 Years 100 Posts

    The MPFI manifold needs the same 55-62 psi as the SFI, and yes, you need the proper scan tool to view and adjust timing on 96-2002 Vortec 5.7s.

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