GM Fuel Pump control scheme

[black maj]

Hi

umm frmo what i have found out/been told... i know that mine fuel pump 
switches on with the ignition and if there is no spark... then will switch 
off about 5 secs later...  but i don't run the pil pressure switch...  and 
i'm also running two efi pumps from the fuel pump relay with no problems... 
so hence it is totally computer controlled.. from the Camira schematic. the 
oil pressure switch is a simple bypass feature if the fuel pump relay 
dies... ie the car will start once oil pressure is reached...

Ben



>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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>>
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