Re: V8-Surge betw 2K and 4k rpm & V8 Surging

[Philip Ross <rossp@blythswood.org.uk>]

I'm replying to two posts at once here but they are on the same subject.

First Dick Krucker gives us a list of the expense Nortland Audi put him 
through to try and cure his surging V8.  I know the feeling.  If your Audi
dealers are anything like ours they are probably don't know one end
of a V8 from the other.  One of them actually told us that this horrid
surging was a "characteristic of the V8".

> If anyone has any ideads I would welcome them...I sent the dealer one   
> article that I found in the Archives about a loose wire between the ECU   
> on the engine and the ECU on the tranny. He said he didn't think that   
> they were connected, but would check it out. That was yesterday....
> Please send to all response to dkrucker@speedware.com
> Thanks for your help.....  

I have now obtained a copy of the Audi manual on this problem with the V8.
It is on pages 24-96 to 24-98 and 01-31.  

The problem on our old V8 was with the "Signal wire for gear change."
"This signal takes back the ignition briefly while changing gear in order to
reduce shift force"
If there is a problem with this it could be that there is a "short circuit to earth
in wiring from contact 51 of Motronic control unit connector to gearbox control
unit" or a "fault in gearbox control unit (permanent short circuit to earth)" or a
"break in wiring between contact 51 of Motronic control unit connector and gearbox
control unit" or a "fault in gearbox control unit (no short circuit to earth when 
changing gear)".

Another problem was "signal input for selector lever position" which "offsets the
increased load created when a driving range is selected by altering the pilot 
value for the idling speed stabilisation."
In which case there could be a "short circuit to earth in wiring from contact 42
of Motronic control unit connector to gearbox control unit" or a "fault in gearbox 
control unit (short circuit to earth is not eliminated by selecting a driving range)" 
or a "break in wiring between contact 42 of Motronic control unit connector and 
gearbox control unit" or a "fault in gearbox control unit (no short circuit to earth 
in P or N)".

I hope this information helps.  It resolved our surging problems.

Then Cobram wrote: 

> I read your post about the resolution to the surging
> problem with  interest. I have a friend with a
> surging V8Q (same one that needs the tranny 'puter).
> Since he knows little or nothing about cars, it will
> fall upon me to check this for him. If you know any
> specifics about the wire (location, color etc.) that
> was loose, I would be very appreciative of the information.

As above.

> I had previously read your posts about changing the fuel
> rail....I never really understood the reasoning behind
> that fruitless move..I still don't.

The reason for changing the fuel rails was that this same Audi
factory manual on page 24-?? insists that the fuel pressure 
should be 4bar and that there is a risk of explosion if it is any
higher.  Ours was 6 bar and in consultation with Audi UK (always
a bad move) our mechanic concluced that the plastic fuel rails 
had cracked inside the metal carriers due to heat.  (I understand
this is a fairly common fault on some cars such as BMW.)  In any
case we obeyed the manual and Audi UK only to discover that the
fuel pressure was and still is 6 bar.  Currently Audi are researching
the issue and have promised to come back to us.

* * * *
These are just the trials of running a car which an Audi dealer in 
London who serviced our car told us was really "just a test bed
for the A8".

Anyway its the last time we buy an Audi prototype!  

Hope you V8 get a smooth ride some day.

Philip Ross.
Edinburgh.