[urq] More Weird UrQ Behavior

Sat Mar 27 12:03:41 PDT 2010

You can't rely on that.  I found O2 readings, logs, etc. to try to capture the source of
the problem only led me  to incorrect conclusion.  I found my readings going way rich -
despite the fact that the pump was cavitating and abruptly starving the engine of fuel.
The problem happened just as you describe - under high load condition.

You can accept what I'm saying with scepticism, or understand I went through this
crazyness.  If you have the original fuel delivery system layout in your UrQ, and you
have an engine that has EFI then it is highly likely you are experiencing the problem of
fuel starvation due to cavitation.  Bigger/higher flow fuel pump does not fix the
problem and in fact may make it worse and result in a burned up brand-new fuel pump.
BTDT and just passing along what I found.  

Not only that, I give a workable solution to the problem.  The solution takes about $100
in parts and a day of work to implement.  If I added up all the other things I tried,
did, etc. before the ultimate fix, it would add up to weeks of wasted time, effort,
money..

Ben 

-----Original Message-----
From: Mike Sylvester [mailto:mike at urq20v.com] 
Sent: Saturday, March 27, 2010 1:32 PM
To: Ben Swann
Cc: urq at audifans.com; 'Quattro List'; afinn1 at gmail.com
Subject: RE: [urq] More Weird UrQ Behavior

I have a surging problem when under full acceleration.
I typically don't get boost over 20psi. (RS2'ed 3B) I thought that maybe it was fuel
starvation, but the A/F meter is saying rich during this time.

Mike

www.urq20v.com

> -------- Original Message --------
> Subject: [urq]  More Weird UrQ Behavior
> From: "Ben Swann" <benswann at verizon.net>
> Date: Sat, March 27, 2010 10:56 am
> To: <afinn1 at gmail.com>
> Cc: urq at audifans.com, 'Quattro List' <quattro at audifans.com>
> 
> 
> Andrew,
> 
> 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 '83.
> 
> 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 error.
> 
> 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
assembly.
> 
> 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 priority.
> 
> HTH.
> 
> Ben
> 
> [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>
> Message-ID:
> 	<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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