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Re: FI pressure drop


I had that problem shortly before the thing refused to start
altogether.  What it turned out to be was the check/overpressure valve
on the side of the fuel pump head(the third hose connection).  The
rubber tip had hardened up and broken off, letting the high-pressure
gas go right back into the tank. Replacing the fuel pump fixed it.  I
no longer have to flick the key a number of times to let the pressure
build up, even after letting it sit a week.  Usually once is enough,
pausing just long enough for the pump relay to time out. With the
ignition on, pump the accelerator once and the injectors should click.
It then starts on the first crank, even in cold weather.  I have had a
bunch of these pump heads that had the same problem.  The problem is
that they're crimped onto the pump head and there's no spares that I
can find.  Usually the motors spin just fine.  The rebuilt pump that I
broke down and bought($$$$) has had the plunger fixed or replaced and
the crimped on cover was replaced by a machined piece that's held on
with allen head setscrews.  The check valve apparently keeps the
pressure up in the loop after the ignition is cut.  You should be able
to see if your injectors leak, pull them out and run the pump by
grounding that wire in the engine compartment.  If one drips, it's a
leaker. I suppose you could check the valve on the pump by opening the
loop at the rear and putting a pressure gauge directly on the end of
the line before the #3 injector.  If it bleeds down really fast after
you cut the pump, you've found the problem, either one of the hoses is
leaky or the pump head is bad.  Mine will hold 20 lbs even after an
hour.  There's specs for it in Bentley if I remember correctly.
>
>I have successfully bypassed, but not fixed, this problem by 
>installing a momentary contact switch around the fuel pump relay that 
>allows me to prime the fuel system without wasting the battery by 
>cranking the starter at the same time.  It works every time and I can 
>hear the air bubbles coming out of the gas line into the tank in 
>front.
>
>My system is wired so that I get into the car, turn ON the key, hold 
>the button in until the bubbles stop, and then release the button and 
>start the engine in the usual way.  I have replaced or swapped many 
>things on these cars, but still don't have proof of exactly where the 
>leak is.  I suspect the injectors.
>
>Jim
>-
>*******************************
>Jim Adney, jadney@vwtype3.org
>Madison, Wisconsin, USA
>*******************************


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