Hi!
The problem described bellow is related to my Audi A6, but since this seems to be related to the Bosch control unit, I post it in this news group as well.
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