[urq] More Weird UrQ Behavior

Ben Swann benswann at verizon.net
Fri Sep 6 10:23:19 PDT 2013

Somewhere I have pictures/plans on making this "fuel capacitor".   I'll see
if I can find and post them.




From: AF [mailto:afinn1 at gmail.com] 
Sent: Wednesday, September 04, 2013 10:55 PM
To: Ben Swann
Cc: <urq at audifans.com>; Quattro List
Subject: Re: [urq] More Weird UrQ Behavior


This is a follow up email. After trying everything including a 034efi pump
in surge tank...The issue was crud in the fuel tank. I got a used tank and
cut off the bottom. Cleaned it. Por15'd it. Permanently removed the filter
sock and used a cleanable in line fuel filter. All issues solved. 


Andrew Finney

1985 urq

Sent from the road

On Mar 27, 2010, at 7:56 AM, "Ben Swann" <benswann at verizon.net> wrote:


I'll lay 95% odds you are starving the pump.  Changing to a bigger badder
pump won't fix the problem.  I had this frustration with my EFI converted

What is happening is the tube coming out of the tank is insufficient to
provide adequate flow to the pump. The fuel delivery on the CIS cars is
designed to have a higher pressure and less flow.  When the pressure is
dropped and flow increased for EFI it basically sucks the fuel faster than
the 3/8" bent tube can deliver.  The result is cavitation at the delivery
side of the pump.  The problem gets worse as the car runs for a while.  I
hit on the problem by finding I could clear the problem by reversing
polarity on the pump for a second - this drives the air out of the lines. 

There are a variety of permanent fixes ranging in complexity - pre-pumps to
surge tanks, in-tank pumps, modifying the bottom of the tank for a much
larger fitting (welding a gas tank!) and fuel cells replacing original tank,
etc.  Look up surge tank and related and you will find this is a common
problem, particularly with drag racing and EFI converted cars.

I toyed with this for over a year - drove me nuts.  Many on the list
probably remember my frustration.  Pulled the tank multiple times, cleaned
the in tank sock, swapped pumps out - the nice 044 pumps and more expensive
pumps only made the problem worse.  I actually had better luck with a
WALLBRO and the OE pump with smaller inlet worked better than the later CIS
pump made for NF/NG!

The pre-pump filter made things worse, and I removed it which helped some,
but the problem persisted.  I did a lot of research and much trial and

I did not want to remove the tank unless I absolutely had to.  So my fix was
to fabricate what I call the "fuel capacitor".  It is simple in concept, but
devil in the details since there is not much room to put something between
the pump and the tank - angles, clearance, kinked lines, etc.  It is a 2"
copper  confabulation - kind of a 45 Deg. Angle between two 6" pipes making
one angled pipe capped at both ends.  The pipe just fits in between the
pump, mounts, brackets and tank.  I had to cut out the unused portion of the
difflock cable assembly - already removed  and being replaced with pnuematic
actuator.  If you need to maintain the cable system then this will be much
harder to implement. 

There is one large outlet that sits at the lowest point in the pipe.  I
should have added a drain fitting because of the lack of pre-pump filter and
probably need to drain it every now an then - I plan to add one later,
possibly with a fuel water seperator that sits sloghtly lower than the

I toyed with a variety of fuel feed and return schemes, but simplicity
prevailed.  Both the inlet and return are installed in  the  "fuel
capacitor".  I need to review what I did exactly, but IIRC there is one
large fitting at the utmost top of the tank - nearly jammed into the feed
line with a very short line. It was difficult to get it installed without
kinking, but once done, there is little to go wrong.

For the return IIRC it it actually teed into the surge pipe offset at slight
angle near the top of the pipe.  I was not sure if it would work, but makes
sense that it does and in fact adds additional but equalized pressure feed
side to not only keep the pump from cavitating, but also keep the feed line
from the tank clear of debris.

In short it works, plain and simple.  The only problem I had was using non
fuel grade line which decided to rupture one day - thank God it was in my
driveway and not on the highway.  So use good hardware and plan it out for a
good reliable solution.

If you  or any listers want picture of the assembly, LMK and I will send
them.  I plan to put this on my site, but these things tend to take low



[Date: Fri, 26 Mar 2010 12:21:43 -0700 
From: AF <afinn1 at gmail.com> 
Subject: [urq] More Weird UrQ Behavior 
To: urq <urq at audifans.com> 
        <ed47d8be1003261221w2a4c5064v1f7af3a500956166 at mail.gmail.com> 
Content-Type: text/plain; charset=ISO-8859-1 

So, at the past 2 track events I've attended with my V8 UrQ I have had a
weird issue with engine cutout at high rpms, usually in 3rd gear, but on the
straightaways in 4th gear. They seem to occur during any throttle position,
like cresting a hill, or accelerating out of a corner, which is somewhat
unnerving. There are no fault codes thrown at all, which makes me think it's
a fuel supply issue. Here's the weird thing, I would say it a fuel pump
relay issue, but wouldn't the engine stall (that's what my old UrQ and Coupe
GT would do on the highway), but in this case there's no power until I
depress the clutch after slowing a little and downshifting, then the power
is all back. The engine never stalls and shuts off! I confirmed it's not a
rev limiter issue by redlining with moderate throttle input and no issues
occured. It's definitely at higher RPM though. Does anyone have a thought? I
thought about relaying the fuel pump, but wouldn't the engine simply stall
with no fuel supply, or will it simply keep running with the car in motion
and clutch out without shutting down or turning on all the warning lights on
the dash?

Any help is appreciated. Thanks. 

Andrew Finney 
1985 UrQ 4.2L ABZ] 

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