GM Fuel Pump control scheme

[Shannen Durphey]

Another advantage to having a parallel control scheme is redundancy. 
Relays also tend to get "burned" due to arcing across the contact points
as they open and close.   This causes a poor electrical connection.  The
oil pressure switch will still allow the pump to operate if this happens.  

In some trucks, the relay is used to circulate fuel for an extended time
after the vehicle is shut off.  This helps prevent vapor formation in the
lines as the engine hot soaks, and aids in hot restarts.  

Throttle body systems don't often show signs of bad relays, in my
experience.  High pressure port injected fuel systems are more likely to. 
In practice, the o.p. switch is not necessary.  I've run my converted 55
chevy since 95 or 96 without an oil pressure switch.  But there's a wire
to the pump conveniently located next to a wire from the battery, just in
case something happens.
Shannen

Bob Wooten wrote:
> 
> This is what i thought but then it can be said that if the CPU is
> controlling the fuel pump, it certainly knows if the engine is running or
> not & can turn off the pump.  I always thought that the oil pressure switch
> was in series with the fuel pump relay for the shut down & that the relay
> gets its power from the Ign. switch but i just checked the diagram in my
> manual & that is not the case & they are certainly in parallel.
> 
> limp home mode sounds most plausible to me, but how does it get the motor
> started?  no oil pressure no fuel, no fuel no oil pressure.
> 
> BW
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