1997 GMC Sierra



February, 4, 2011 AT 1:46 AM

I have a 1997 GMC Sierra K1500 with a 5.7L Vortec V8. When I press on the accelerator the engine surges. It seems to me its not getting enough fuel and when it starts to surge I lose oil pressure. I put a brand new fuel pump, 3 actually, in it, changed fuel filters regularly, new plugs and wires, mass air flow sensor, throttle positioning sensor, and new fuel pressure regulator. I drained the tank and cleaned it out thinking I might have had a dirty tank. I'm considering putting a brand new tank with a new pump and sending unit. What should I do next because I'm not what is wrong with the truck? Thank you for the assistance.

2 Answers



February, 4, 2011 AT 1:57 AM

When ignition switch is turned to ON position, PCM/VCM turns electric fuel pump on by energizing fuel pump relay. PCM/VCM keeps relay energized if engine is running or cranking (PCM/VCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM/VCM turns pump off within 2-20 seconds after key on.
As a back-up system to fuel pump relay, the oil pressure switch also activates fuel pump. The oil pressure switch is normally open until oil pressure reaches about 4 psi (.28 kg/cm2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained and operates the fuel pump.
Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close.
Oil pressure switch may be combined into a single unit with an oil pressure gauge sending unit or sensor.
PCM/VCM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump, enabling PCM/VCM to determine if fuel pump is being energized by fuel pump relay or oil pressure switch. A failure in this monitored circuit results in the setting of a related diagnostic trouble code in PCM/VCM memory.



February, 4, 2011 AT 9:41 PM

Ok thanks for the help by the way. I know the trouble codes I've been getting have been for the O2 sensors and the other code is a random misfire. Is it possible that if either the fuel pump relay or the oil pressure switch are failing could that cause a random misfire? I checked for vacuum leaks and replaced my plugs and wires because I wasn't sure what cylinder was misfiring. Someone had mentioned to me that the egr may be bad. Would a faulty egr valve cause these problems? Once again thank you for the assistance.

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