[s-cars] "Antilock off" caused by diff lock vacuum failure

[chris chambers]

Congrats on the fix!

If you end up needing a replacement vacuum resevoir I can pull
one off my 93 Urs4 parts car.


Chris



----- Original Message ----
> From: Wayne Dohnal <wd43 at hevanet.com>
> To: S-car list <s-car-list at audifans.com>
> Sent: Sat, November 7, 2009 5:12:16 PM
> Subject: [s-cars] "Antilock off" caused by diff lock vacuum failure
> 
> I've been chasing an intermittent "antilock off" light for a while and 
> haven't noticed any postings about what failed in mine.  The first 
> breakthrough was noticing the light seemed related to acceleration.  The 2nd 
> was noticing that it was directly related to vacuum and boost levels, and 
> the 3rd was that the diff lock's green light went came on and went off with 
> the antilock off light.  I actually had 2 failures: (1) The vacuum check 
> valve under the back seat was open in both directions, and (2) the hose 
> nipple had broken off of the vacuum resevoir in the trunk.
> 
> I replaced the check valve with a $4 generic version from the parts store. 
> It's very difficult to get to the clamp on the original check valve so I 
> just added the new valve in line with the old one.  I glued the nipple back 
> onto the vacuum resevoir, but this is a type of plastic that glue doesn't 
> stick to very well so it may or may not stand the test of time.  Besides 
> fixing the antilock off problem I'm noticing a smoother application of boost 
> pressure.  Before the fix, the boost would climb to about 20 psi then 
> abrubtly back off to 10 psi or so.  Now it climbs to 15 psi, smoothly tapers 
> off, and holds at 15.  I assume the leak was causing the ECU to be getting 
> corrupted vacuum/boost data.
> 
> Wayne
> 1994 S4 
> 
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