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Re: problem with S2 92
Having the engine shut itself down at 4000 RPM sounds typical of an Audi
engine that is sensing a potential problem and is allowing you to use it in
"limp home" mode. Since you only see the problem under boost my thinking is
that either the engine is producing too much boost, or the sensor in the ECU
thinks that the engine is producing too much boost. The typical service
diagnostic is to attach a separate boost gauge to the intake manifold and
observe the boost pressure under certain load conditions. There is a boost
curve that is expected for your car ... perhaps you can get a copy of this
graph from a dealer, or someone who happens to have the graph for the S2 ...
If the engine shuts down only at *4000*, it's probably not overboost
(which leaves only 99 other things!).
On some older beasts (the UrQ, fer instance), the intake manifold air temp
sensor would exhibit this same symptom -- at 4000RPM if it is "out of
range" the ECU will shut down the engine, but *only* if under boost...
if you ease the engine to 5000RPM and then "boost" it, it runs right
to redline with the faulty sensor.
I'm pretty sure (I certainly *HOPE*) Audi doesn't use that same <expletive
deleted, but it's a past participle> air temp sensor, but they may well
have kept the same algorithm. (As a quasi-non-random experiment, if you
can easily access the ECU, unplug and replug it a coupla times [engine/
ignition *off*, natch!] and see if this has any effect on the problem.)
-RDH