[Biturbos4] Detecting "limp" mode?

j y jimnetpa at yahoo.com
Mon Mar 10 22:15:57 PDT 2008


Let me take a stab at your ????s
Are you chipped? - If you are chipped there is a MUCH greater chance of your S4 going into limp mode from overboost than if you are not.
Yes, ambient temperature, fuel quality, and fuel pressure have an impact on boost capacity. Are you still using the stock fuel pressure regulator and what grade of gasoline are you using? Are you always using the SAME octane level (i always use 93 becausemy S4 is heavily modded stage 3 tip). 

Also, when was the last time you changed spark plugs? Newer plugs give your S4 a cleaner burn (hotter flash-point during ignition). How are your injectors? Maybe an injector is sticking under boost. If so, try a fuel injector cleaner - never hurts. Finally, if you don't have VAG-COM, BUY IT!  Having VAG-COM is well worth the purchase price - many times over! VAG-COM will take most of the guess work out of diagnosing issues with your S4.  

Based on your email, it sounds like the only mod you have are the aftermkt DV valves. If that is the case, then the boost levels you are seeing, is quite normal for a non chipped S4. If you don't have a chip - buy one - you will NEVER drive a non chipped S4 again. As far as a Stage 3+ S4 like mine - it's worlds apart (20 psi @ WOT on a early generation X-chip & manual boost controller) from a non chipped S4. 

Good luck.

----- Original Message ----
From: Chris Newbold <chris at newbold.org>
To: Bi-Turbo Audi S4 Audi Fan Group <biturbos4 at audifans.com>
Sent: Monday, March 10, 2008 12:50:02 PM
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 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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