[BiturboS4] presure leaks and important information about MAF

California Fields cfields72 at hotmail.com
Thu Sep 11 16:09:30 EDT 2003

Group, Mikka's post is good place for me to offer some advice about the
diverter valves (just from my experience). While I recommend the Bosch
diverter valves, they won't last forever since they are rubber/plastic
(instead of metal like the other aftermarket ones). I recommend removing the
Bosch diverters after each 5k mile oil change and quickly checking for their
ability to hold vaccuum by sucking on the nipple (yes, I know that sounds
funny). If you want exact instructions, write to me directly.  It only takes
about 10 minutes to remove the valves and another 10 to inspect and put back
into place.

Another way to see if something is wrong with the valves (as Mikka pointed
out), is to record block 115 on the VAG. Some tell tail signs of a faulty of
valve are if the actual boost does not fall off as quickly as the requested
boost between shifts (boost lingers, or worse continues to increase), or if
the boost never builds to requested levels (although that could be caused by
boost leaks elsewhere in the system).


<DIV>Carter Fields, San Francisco</DIV>
<DIV>2001.5, GIAC-X, Miltek 3" cat-back, Strat. shifter, Strat. DVs,
A-pillar boost gauge</DIV>

>From: "Miikka Salonen" <miikka.salonen at kolumbus.fi>
>To: <biturbos4 at audifans.com>
>Subject: [BiturboS4] presure leaks and important information about MAF
>Date: Thu, 11 Sep 2003 09:43:33 +0300
>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).
>BiturboS4 mailing list
>BiturboS4 at audifans.com

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