[s-cars] Go. No go. And; go.

[Bill Mahoney]

Hey Brett,
Thanks for detailed response.  I am pretty convinced that it is a Fuel Pump
Gone Bad (FPGB)tm.
I had noticed over the last couple / few weeks that when I opened the car
via remote and got in, that there was a wheeering sound that seemed to come
from underneath the driver's seat... I thought that it was just some seat
motor having an Audi God Moment (AGM)tm.
I had about 20 minutes to pull the codes last evening 
553  MAF          07-00 signal too low
537  O2 sensor    11-10 control limit not reached intermittent
513  Eng. Spd sensor G28  03-00 No signal
But, while doing this I decided to try to locate this wheeering sound which
turned out to be from the back seat near where the battery is.  I didn't
have time to nail it down.  
I am presuming that this is quite possibly / probably the FP in its death
rattle.  I am guessing too that doing the fuel pump in an avant will be a
little easier with more head room to work with.
At any rate, I have a new FP and FPR in route and if I get it by tomorrow
(not likely) I could have an Easter Pump Install Party (EPIP)tm.
Short of that... and double d'oh for this, I have to insure that the A8 is
near empty and then siphon out as much gas as possible. 
I am thinking to back the pig onto rhino ramps near the A8 and let er rip.
I don't really like this at all, although the prospect of a massive fire
ball is kind of exciting.  
Thanks!
Bill~all gassed up~M

  

-----Original Message-----
From: Brett Dikeman [mailto:brett.dikeman at gmail.com] 
Sent: Thursday, April 09, 2009 8:18 AM
To: Bill Mahoney
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] Go. No go. And; go.

On Wed, Apr 8, 2009 at 11:07 AM, Bill Mahoney <wmahoney at disk.com> wrote:
> Maybe O2 sensor?

Motronic is open-loop during startup and for a few minutes until the
O2 sensor warms up.  Also, O2 sensors rarely go "bad"; their response
time just increases with contamination.  If the sensor was
disconnected or had a bad connection, you would see a check engine
light or have a fault code.

Aside from major fuel/ignition problems (ie coilpack failure, fuel
pump relay/pump failure, pressure regulator, etc)- what would affect
startup mixture and idle speed would be the ECU coolant temp sensor,
MAF sensor, idle stabilization valve, and...drumroll please...intake
system leak.  The ISV obviously wouldn't affect acceleration, but the
ECU temp sensor and MAF sensor sure would...and sudden stumbling under
acceleration.  Because of the ease of checking, it is worth it to
check the vacuum line to the FPR; if it fails or becomes disconnected,
the engine will run very rich at idle.  You'll also eventually get a
CEL on this, because the ECU will try to compensate for the rich
running.

Murphy's law is that it will be the pump if I say this, but- there are
a number of other things you need to be checking out before you commit
to a major job like replacing the fuel pump. At the very least, pull
codes using VAG-COM (blink codes don't cover intermittent fault codes)
*AND* check the first memory block to see if values are within norms
(but note that there are very specific conditions for the ranges given
in the Bentley- mostly around running time, coolant temp, battery
voltage.)

Start with the easiest stuff to test, even if the likelyhood is low.
If you need to do a boost pressure test, raid the tupperware drawer; 1
cup rubbermaid containers (the kind with the tan covers) are a
near-perfect fit for the hose off the MAF.  Just be REAL careful not
to over-pressurize the system more than .5 bar above normal boost
levels.

Really, your first stop should be here:
http://www.sjmautotechnik.com/trouble_shooting/20vboost.html

Brett