[Biturbos4] Detecting "limp" mode?

Wilson Northrup northrup at crazybug.com
Tue Mar 11 00:50:29 PDT 2008


1. Is the lower PSI when the car is cold? or is your oil up to temp?

2. my understanding of limp mode (or what i've experienced in my car which 
appears to be limping) is 10VAC, less than zero on gauge.

3. i haven't heard of coming out of limp without restarting the ECU (car 
off/on), but that's not to say it's impossible.

On Mon, 10 Mar 2008, Chris Newbold wrote:

> 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.
> -Chris
> 2001.5 S4 Avant 6spd
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