GM Fuel Pump control scheme

[Shannen Durphey]

This circuit offers no engine protection.  If the fuel pump stops due to low
oil pressure, the engine will continue to run until it has consumed the fuel
in the carburetor.  This is more than enough time to waste the crank and
bearings.

Anybody wanna bet the "safety switch" fulfills a federal requirement? 

Funny thing about the Luvs, the o.p. switch would often fail on the road.  So
to get the truck home, I've seen guys run till the carb was empty, then crank
'em for a bit so the fuel pump would refill the bowl and drive till the bowl
was empty again.  They'd come into the shop for a $5 oil pressure sender and a
$35 starter at the same time.

Shannen

ae2598 at wayne.edu wrote:
> 
> Since the Vega was brought up earlier, I figured I'd dig out my '71 shop
> manual and take a peek at the theory of operation.  I quote:
> 
> "The fuel pump is energized when the ignition key is in the start
> (cranking) position.  After the engine starts, the pump receives current
> through the oil pressure safety switch as long as there is approximately 2
> pounds of oil pressure.  If, for any reason, the oil pressure drops below
> 2 pounds, the contact is broken at the pressure switch and the pump is
> de-activated."
> 
> The wiring diagram shows one terminal of the OP switch connected to the
> starter, just like the old-school distributors.  This must be the cranking
> bypass feature.
> 
> Now, they don't really define what they mean by "safety", but I'll bet
> they're thinking about collision, fire, or some other catastrophe that
> would cause the crank to stop turning.  Protection of the engine is
> presumably left up to the operator.  The intent must be similar to Ford's
> "slam switch" that they so cleverly hide in the trunk, which opens the
> fuel pump circuit upon impact.
>
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