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[T3] FI fuel pump ordeal

I think I posted a few weeks ago that I had been having some trouble 
with my FI fuel pump. The symptoms were that nothing came out of the 
outlet while lots was coming out the overflow.

I removed the pump head from the motor, leaving the motor installed 
in the car. Disassembly and inspection revealed that there is a 
little piston in the pressure relief assembly which has a rubber 
nipple on its end. This rubber tip is actually part of sort of plug 
which fits all the way thru the piston and comes out the bottom. Thus 
it installs in a hole in the head of the piston.

After a "mere" 34 years, that rubber plug broke into 2 pieces. One 
piece stuck in the outlet hole, preventing any flow there, while the 
other piece pushed out the back of the piston, letting all the pump 
flow pass thru the hole in the piston and out the overflow outlet.

To be fair, I believe Keith described the same failure in a pump of 
his several years ago.

I looked around in vain for a source for little rubber plugs this 
small and found nothing. I was prepared to modify the piston when I 
talked to the head of our machine shop and he convinced me that I 
could make a replacement part out of Teflon. I didn't think I could 
do it, just because the part was so small, but I did it, and it 

The aluminum cap that covered the bore where the piston lived was 
also corroded, so I made a replacement for it out of brass.

I put everything together a couple of weeks ago, with new O-rings and 
it's been working fine since then.

One more possibly interesting detail. This car has had a long term 
problem of needing the fuel ring to be primed before it would start 
easily. Now that tendency seems to have gone away. It makes me wonder 
whether the aging rubber plug was letting the pressure leak out of 
the fuel ring and that the new Teflon plug has fixed that problem. I 
had worked over all the other suspects in this car's FI system 
without ever seeing any effect on the startup problem, so I suspect 
that this may have been the root cause.

Unfortunately, it has also turned colder here, so this problem MIGHT 
come back the next time it gets warm.

This pump failure worries me, because we have a LOT of these electric 
FI fuel pumps out here, all with the same potential problem. The 
little rubber part won't last forever on any of them and slowly they 
are all going to die. My plan is to tool up to make a number of these 
parts, so I can repair pumps for anyone. In the meantime, I intend to 
rebuild some of the extra pumps I have here, just so I have known 
good spares. I'll probably carry a couple in the caravan to the next 

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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