On Mar 21, 11:28 pm, aarcuda69062 wrote:
> In article
> <1174508586.907025.68...@b75g2000hsg.googlegroups.com>,
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> "N8N" wrote:
> > > > I don't like the oil pressure switch idea simply because there may be
> > > > situations where you make the educated decision to fry your engine to
> > > > get out of harm's way. but that's just me.
>
> > > Not sure I understand...
>
> > Let's say you spin a bearing in the hammer lane of the freeway, or you
> > run over some unavoidable debris that holes your oil pan. Oil
> > pressure suddenly drops to zero. However, to get over to the
> > shoulder, you still need power to merge through three other lanes of
> > traffic... Also, with the oil pressure switch, you won't have
> > immediate fuel pressure for lightning-fast starts unless you also
> > incorporate some kind of timer running off the rising state of the
> > ignition switch; the engine will have to crank over and build oil
> > pressure before the pump will start feeding the engine.
>
> When the OP stated that this installation was in an older car, I
> assumed* it was a carbureted vehicle.
> (* TMOAFU's)
>
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> > > > The VW relay works like this; when power is applied to it (i.e. you
> > > > turn the key on) it will run for 5 seconds and then shut itself off -
> > > > this pressurizes the fuel rail for initial startup. Then when it
> > > > starts receiving pulses from the coil, it will latch in until it no
> > > > longer receives a signal from the coil.
>
> > > Didn't know that was how VW did their fuel pump relays.
> > > Gotta store that one in the data banks.
> > > Thanks.
>
> > If you or another poster wants scans of the factory diagrams showing
> > how to wire it up, I can try to accomodate... I am actually
> > contemplating just this kind of thing for my '55 Stude if I ever go
> > with an electric fuel pump. (the stock mechanical pump is LOUD and I
> > don't know why; I've tried several different pumps including one NOS.
> > Works fine, but it sounds like a rod knocking at idle, which is bad.)
> > So I've already taken a stab at puzzling out the factory diagrams (I
> > have several Bentley manuals for various VW's I've owned) but haven't
> > gotten as far as sketching a simple "retrofit" diagram. I think you
> > probably just need switched power, ground, battery power, coil, and
> > output to fuel pump, but I can't swear to it. i'd probably throw an
> > "ice cube" at it to take the load off for a heavy-draw racing pump.
>
> I'll take a look thru Mitchell on Demand and see if I can pull up
> a schematic.
>
> > i'd be willing to bet that other mfgrs. use a similar fuel pump
> > control scheme; I just happen to be *familiar* with VW's so that is
> > what I suggested.
>
> Similar in that a tach signal is needed, but they usually rely on
> the engine computer to recognize it and thusly control the FP
> relay. That VW has this ability self contained in the relay is
> intriguing.
> A pre computer era example would be the Chevy Vega (spit) and its
> variants, carbureted engine, electric in tank fuel pump
> controlled by an oil pressure switch.
> A post computer GM car would have the FP relay and the oil
> pressure switch in parallel
Mid 80s, a friend of mine had an Audi that stopped working that we
could not figure out; eventually he accidentally knocked the wire
loose from the tach input and it fired right up. the tach input had
shorted out, and that was killing the feed to the relay for the fuel
pump.
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