GM Fuel Pump control scheme

[Shannen Durphey]

It's been stated several times that there is no practical need for the switch.
In series it would not be preventative because the switch opens too close to
zero psi to save an engine on the highway.

I have told you what I've seen as a mechanic, that the switch is useful as a
backup device to power the fuel pump.  This is not based on theory, but real
world experience.  I have brought cars into the shop that are running solely
on the oil pressure switch.  You can tell as soon as you start the car that
the relay's not working. And I've spoken to customers about it enough to know
that quite often, they have no idea the relay's bad.  Sometimes they don't
even know that the car's taking longer to start!  But they surely notice that
things are better once a new relay's installed. 

Bruce tried to tell you that GM does things that don't always make sense.  If
you don't know the story about the 63 split window coupe Vette, you might be
interested in doing some reading.  There are few sound engineering principles
involved in the decision to put that car into production.

This fuel pump relay discussion is one that floats around the list waiting to
catch newbies.  It happens time and again.  Look through the DIY archives,
you'll find different flavors of it.  

So the new question is, do you really feel so compelled to ask why?  Finding
the answer to this question could make for a great obsession.

Shannen

WEG1192 at aol.com wrote:
> 
> Hmmm, this certainly blows a major hole in my theory. So the question
> remains, exactly what is the OP switch for? If it were in series, I could
> understand it as a safety from locking your engine, but in parallel, I for
> one don't see the need for it. JW
----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org