[Biturbos4] Detecting "limp" mode?

Brandon Rogers brogers at terrix.com
Mon Mar 10 10:21:51 PDT 2008

I would pull the codes and see what the ECU tells you before you do
anything else.  You can use VAG COM - personally I have Pro-Diag and
love it.

'01 S4
'84 ur quattro 20Vt

-----Original Message-----
From: biturbos4-bounces at diablo.audifans.com
[mailto:biturbos4-bounces at diablo.audifans.com] On Behalf Of Chris
Sent: Monday, March 10, 2008 10:50 AM
To: Bi-Turbo Audi S4 Audi Fan Group
Subject: [Biturbos4] Detecting "limp" mode?

For the last several months, I've noticed that under many circumstances
I'm only getting about 6psi of boost (according to the AWE center-vent
gage). Other times I'll get upwards of 8-9psi, which is what I'd thought
was the stock limit. My impression is that I used to get 8-9psi far more
regularly than I am now. I've pretty much ruled out intake leaks, as
this apparent change in behavior has persisted despite replacing all of
the rubber in the intake system with Samco bits. I also have Bailey
diverter valves, and so am less inclined to suspect them (as compared to
stock valves).

Some how I'd gotten the idea that 6psi was the "safe" limit used when
the ECU dumped into "limp" mode due to some detected failure or error

So, three basic questions:

1. Should WOT always result in 8-9psi of boost while in the 2500-5000RPM
range? Or are there other factors, such as ambient temperature,
transmission gear and road speed?

2. Is "limp" mode always accompanied by a check-engine light? Is there a
definitive way to determine if I'm in "limp" mode via VAG-COM?

3. Can the ECU toggle in and out of "limp" mode "frequently"? For
example, during my usual 40-minute commute I've seen both 6psi-limited
behavior as well as 8-9psi limited behavior.

2001.5 S4 Avant 6spd _______________________________________________
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