Short run - cold start problem with A6 1.8T 1999 mod
 

Hi!

Problem:
I have for the second time run into a cold start problem with my Audi A6
1.8T (AEB) 1999 mod. The problem is as follows: After car has been run for a
short period (< 1 min), parked and left for some time (> 1 hour), the motor
fails sto start. This is known as the "Car Wash" syndrome or "Flooding"
syndrome. There are no diagnostics code from the control unit. I both cases
I had to take the car on a truck to the Audi dealer. Their standard
"procedure" is replacing spark plugs and then everything is "fine". In my
mind this is treating the symptoms rather than the source. The failure
described here seems to be a common problem for many German care makes and
most pointers are haeding at the Bosch engine control unit which is located
in most German cars. There are different opinions on wheather this is a
"bug" or a "feature". Let me explain why:

The "bug" hypotesis:
The ECM unit have three phases of the engine control program: Cold-Cold,
Cold-Warm and Warm-Warm, where the first is the temp. of the coolant andt
the second is the temp of the engine. When the engine is started (cold) the
Cold-Cold program is used to flush gas into the engine (same effect as the
old choke), then quite fast moves into the cold-warm program mode which
gradually dilute the gas mixture until the warm-warm mode is reached. The
problem seems to occure when the engine is stopped in the Cold-Warm mode.
Some people speculate that there is a software bug which locks the control
unit into the Cold-Warm mode next time the you try to start the engine -
unsucsessfully. Because of the lock-up next time you try to start the
engine, to little gas is injected into the combustion camber and the engine
faiuls to start. The other hypotesis is that there is still a to rich
mixture in the combustion camber when the car is stopped in the cold-warm
mode. Then, next time the engine is started in the cold-cold mode, the gas
flush into an already flooded chamber gives an ignition failure. This
hypothesis is well supported by coated spark plugs which is a typical
phenomenon observed when this problem occures.

The "feature" hypotesis:
The cold-wars start problem can also been seen as a "feature", as it is ment
to protect the CAT from beeing flushed with unburned gas. Therefore one of
the work around solutions on the net is "...cranking the engine for at least
30 sek with gas pedal floored. This will eventually flush air through the
engine and dry up everything. Many people reports that this seems to be
working.

Are there anyone, especially with particular knowledge to the Bosch Motorinc
control unit which can explain whats really going on here? Or, eventually
point to official sources of information giving a "official" solution to the
problem? It could be a program upgarde or a "safe" work-around" procedure.

Thank you!

Jacobsen