GM Fuel Pump control scheme

[Dave Zug]

ECM runs the pump for 10 sec before engine start to give pressure to the
system, in case it had bled down after the car was off for a long time.

When the engine starts, the ECM tells the pump to run continuously, but when
the oil pressure comes up (about 3 or 4 engine revs during cranking) the oil
pressure switch ALSO tells the pump to run.

If your ECM relay is bad, the simptoms will be, when you crank the engine it
does not start until a dozen or so cranks. This is because the fuel ump will
be told to go ON after the cranking makes enough oil pressure to turn the
fuel pump on, then shortly thereafter the pressure is up enough for some
fuel to go into the injectors. The ECM did not get to pre-pressurize the
system.

You could put a 'security' switch in to not allow the ECM to run the fuel
pump unless the security switch was turned on. The car would fire up anyway.
Controls-101. ;-)


----- Original Message -----
From: Wes Branchflower <hemi_265 at hotmail.com>
To: <gmecm at diy-efi.org>
Sent: Saturday, January 27, 2001 6:52 AM
Subject: Re: GM Fuel Pump control scheme


> I thought the ECM would run the fuel pump for approx 10 seconds, then
stop.
> My brother used to have a VL commodore, when he turned the ignition to ON
> (not start) the pump would go on for about 10 seconds, then stop. (I know
> this cause his fuel pump was REAL noisy ;)
>
> This leads me to think that the fuel pump is activated by the ignition,
for
> a brief 'turn on' time, after which, is turned off. When the engine starts
> (off the pressure already in the fuel rail), the engine's oil pressure
> switch would take over the control of the fuel pump. This makes it so if
> ever you loose oil pressure, your engine will shut off. (saving the motor)
>
> Does it seem right?
>
> remember this is a nissan S6 found in the VL's. not a GM.
> But i think it could be a very similar design.
>
> If it doesn't already do this, i'm definetly making this modification on
my
> engine.
>
>
>
>
>
>
> >From: ae2598 at wayne.edu
> >Reply-To: gmecm at diy-efi.org
> >To: gmecm at diy-efi.org
> >Subject: Re: GM Fuel Pump control scheme
> >Date: Sat, 27 Jan 2001 08:49:14 -0500 (EST)
> >
> >I guess that's why the car will still run if you disconnect the oil
> >pressure switch!  I've seen more than one S-10 4-cyl. switch fail and
leak
> >profusely, it happened to mine a few years ago and it was late at night
so
> >all I could find was a pipe plug to plug the oil passage.  truck ran fine
> >with the wiring harness dangling..
> >
> >  On Sat, 27 Jan 2001, Shannen Durphey wrote:
> >
> > > 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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