[BiturboS4] presure leaks and important information about MAF

Miikka Salonen miikka.salonen at kolumbus.fi
Thu Sep 11 10:43:33 EDT 2003

Hi guys

Now it was my turn to blow bosch bypasses. Last few days my car was
not builder boost very well. I logged group 115 with vag-com and could
confirm, that boost building was slow and boost did not hold at high
rpm. I drove to local MTM-dealer to have them transfer 3bar sensor and
chips from my old car's ECU to new ECU (old one had some problems) and
driving there (200km) I noticed that if I in middle of acceleration
release pedal and push it again, presure drops and don't build again.
So I asked dealer if he had forges and they had. We replaced bypasses
and found that both bosch where broken.

We went to test drive and boost was comming quite well but engine was
riching the mixure too much (ECU compensates failing MAF, normally the
MAF goes little by little and ECU can fix that with compensation).We
tried with test MAF but that did not help as much as it should have.
So they pressurized the intake and found one broken low pressure pipe
and to injectors where leaking becouse o-ring was broken! After that
we put orginal MAF back (test MAF had other problems) and car worked
quite well. I still have to buy a new MAF soon, but I can drive with
old one and little rich mixture just cools down engine better :o)

This problem with MAF is really common. Because ECU will learn this,
car continues work almost like nothing was wrong until MAF starts to
give almost random information or compensation becomes too incorrect.
If your car seems to sometimes lose power and sometimes works well, it
is probably the MAF. If you have VAG-COM, this can be tested with
measurement group 033. Warm engine first and then accelerate. Readings
should be positive something, probably over 10%. Then drive constant
speed. Now without acceleration, mixture should be normal. That meens
readings should be something between -5% and 5%. Or at least jumpping
between negative and positive. This is how I remember it, but I will
ask the dealer to be sure. I already got instructions how to reset
this MAF compensation after I replace the MAF (that is important,
otherwise it takes long time to learn new MAF).


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