GM Fuel Pump control scheme

[ae2598 at wayne.edu]

Well, its for the "limp home" mode of the monojet carb, of course! :)

I'll have to look at my vega wiring diagrams, I would've sworn the in-tank
pump runs whenever you've got the key in the run position.  'Cept of
course on the cosworth, where the ECM closes the relay.  Incidentally, it
was a common problem for the fuel pump relay to stick closed on cozzies..
You could sometimes open the contacts by slamming the hood, or pounding on
the cowl near where the relay is mounted.  Mine would do it too, you'd
walk away from the car and come back 1/2 hour later to the pump still
running..


On Sun, 28 Jan 2001, Bruce Plecan wrote:

> 
> And you would explain the Vega, how?.
> Bruce
> 
> 
> 
> From: <WEG1192 at aol.com>
> > To me its obvious that Steve Ravet was right in that the OP switch is used
> to
> > keep the pump running during CPU failure, otherwise limp home wouldn't
> work
> > period. I can also say for certain that the ECM keeps the pump running as
> > long it recieves ignition pulses from the distributor. To say that the OP
> > switch is a backup for the F/P relay doesn't hold much weight to me. Also,
> > the OP switch isn't a safety to shut down the pump since if the engine
> stops
> > with the key on, the ECM will shut the pump off due to the lack of
> ignition
> > pulses. The only plausible resaon left is to keep the pump running during
> > limp home mode. JW
> 
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