The ND (original NipponDenso pump) and Bosch L-jetronic pumps were
very tired at this point... Both Bosch K-jetronic and Pierburg
(a K-jet replacement pump) gave good delivery at needed pressures,
but the damned adjustable pressure regulator didn't function properly
if the return flow to tank wasn't large enough. So I still needed
two fuel pumps. Rats.
From: Eric Ekberg "firstname.lastname@example.org"
Subject: Fuel Pump Warning
This is something I've not seen much discussed on the list, but I
believe it to be a big trouble spot. I have now personally witnessed
fuel pressure drop on 3 mk3's with stock fuel pumps. All 3 are in the
range of 250-350 rwhp (2 92's, 1 91). I have heard claims that the
stock fuel pump is good for 400+ rwhp, but IMO that's horse shit. My
fuel pump wasn't supplying enough fuel at stage 4.
How do I know if my fuel pump's good enough? Get a fuel pressure guage
and put it in the cabin where you can look at it while you boost.
Mounting it in the engine compartment doesn't tell you jack shit, unless
your on a dyno with your hood up. I personally ran -3 steal braided
fuel line into the cabin, but autometer just came out with an electric
gauge to the tune of $200. If your really scared to run fuel into your
cabin on a permanent basis (and you should be) you can always run the
line temporarily through the window just to see what's going on. If your
fuel pressure goes up under boost and then starts to fall back down at
higher rpm, your fuel pump ain't cutting it.
The solution? Obviously a new pump. I chose the 300z twin turbo pump
on advice from several others. It's an easy modification. My only
problem was that my regulator could not handle the excess volume at
idle. The problem was that there is a restriction in the return fuel
line. Bolted to the block is a 90 degree metal bend. One side is wide
open, the other side has a tiny hole in it for the fuel to pass
through. Drill this hole out and there are no more restrictions,
besides the size of the return line itself.
To all of you at stage 3+ who don't have a cabin mounted fuel pressure
guage or an EGT your taking some big risks with your engine.