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Thread: Fuel Pump Control

  1. #11
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    Quote Originally Posted by jderekt View Post
    Has taken me a long time to get back to this (truck has been sitting a lot) but I've finally figured out this issue. Turns out the oil pressure sensor, which in 98 was still part of the pump circuit, is slow to bleed off pressure. Which keeps the pump running until the pressure drops to 10psi or so. Which means I've apparently got debris in the sensor.....sensor was replaced when motor was rebuilt. So new sensor going in after I purge that oil passage a bit.
    And this circuit is going to be removed to eliminate this completely.

    Sent from my SM-G950U using Tapatalk
    And here I always thought I had a sticky fuel pressure relay. I'll have to pay attention to if mine lingers longer cold than warm to confirm. I can also watch the oil pressure gauge too I imagine.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, Whipple, awaiting 411.
    2004 Corvette Z06 with longtubes.

  2. #12
    Joe (Moderator) joecar's Avatar
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    Not all GM vehicles have this feature... do we know all which ones do...?

  3. #13
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    I know the 88-95 TBI trucks had it as well as the 96-98 Vortec trucks ( pre-LS). In 8 lug fashion, the early engines lived until 2000. GMT400 platform stuff. I haven't gotten that deep into GenIII and newer. When you turn the key to start, it bypasses the oil pressure switch. Once it's running though you need oil pressure to stay running.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, Whipple, awaiting 411.
    2004 Corvette Z06 with longtubes.

  4. #14
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Supercharged111 View Post
    ...
    Once it's running though you need oil pressure to stay running.
    This is a different configuration than what jderekt posted above...
    his 2 redundant paths implies an OR function (EOPS in parallel with FP relay),

    whereas your configuration implies an AND function (EOPS in series with FP relay)...
    unless the ECM is involved (when it sees EOP fall down it shuts down engine)... is this how it works...?

    from what I see on LS1tech, this would have saved many engines from the notorious pinched o-ring problem.

  5. #15
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    It doesn't actually bypass, it is a parallel scenario, but that oil sensor electrical path is closed when you first hit the key. There must also be a time delay in there too.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, Whipple, awaiting 411.
    2004 Corvette Z06 with longtubes.

  6. #16
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    Quote Originally Posted by joecar View Post
    This is a different configuration than what jderekt posted above...
    his 2 redundant paths implies an OR function (EOPS in parallel with FP relay),

    whereas your configuration implies an AND function (EOPS in series with FP relay)...
    unless the ECM is involved (when it sees EOP fall down it shuts down engine)... is this how it works...?

    from what I see on LS1tech, this would have saved many engines from the notorious pinched o-ring problem.

    From what I have read, that EOPS circuit can kill a motor if oil pressure is lost or if the switch fails. I actually found this completely by accident
    while reading a forum thread. So it seems at least with my rig, this circuit is the fuel pump control circuit once oil pressure is detected.

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