[Biturbos4] Detecting "limp" mode?

Joel Liggins quickaudi at gmail.com
Wed Mar 12 17:53:51 PDT 2008


Last time you cleaned/oiled your Bailey DVs?
Have you pressure tested for boost leaks (Samco doesn't mean you haven't
blown a hose off)
What maintenance have you performed in the last 60k miles? (spark plugs, air
filter, clean throttle body, fuel injector cleaner, etc.)
Limp mode doesn't necessarily mean you'll get a CEL.
Have you found any codes via VAGCOM?
Once in limp mode, you're there until you cycle the keyswitch.
How many miles on your car?  Some seem to have had wastegate line issues...
Are your EGTs stock?


-----Original Message-----
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 condition.

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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