Re: Boost Induced Woes

[donohue@azstarnet.com (Terry Donohue)]

On Mon, 22 Sep 1997 11:57:45, Kerry Griffith wrote:

>I still have the following symptom: When I floor it and
>boost builds, the car will suddenly lose power and boost
>and run really rough. If I ease off on the accelerator, the
>car runs great. I've replaced the IC to TB hose, the
>sparkplugs and the fuel filter. I'm in the process of finding
>a shop vac to do the pressurization test to find a leaky
>vacuum line. If that produces no results, I'll be back to
>square one.

I had the same problem with my '90 200TQ; however, this problem followed a
repair at a local garage to fix the infamous exhaust manifold leak problem;
unfortunately, this eventually involved removing the head to get the broken
studs out.  Anyway, my problem was similar; the engine would cut out at
high boost (over 1.5 bar), not necessarily at full throttle; backing off
slightly would instantly cure the problem.  Careful listening to the engine
suggested slight pinging occurring just before the engine would cut out.
The fault codes showed no problem.  I came up with a theory that suggested
the ignition control unit was hearing knocking, but the maximum retard it
could give wouldn't fix the problem, so it would cut the ignition.  And
yes, upon careful checking of the cam/distributor timing vs. the crankshaft
showed that the head had been reinstalled one tooth advanced!  Retiming the
distributor (why is this done statically where every other car I've owned
is timed dynamically, with a timing light?) totally solved the problem.  At
the moment, I'm running the cam one tooth advanced, but some on the list
think this is better; I'll be performing some comparison tests to see which
works better.  I don't know if this could be your problem (timing belts
have been known to jump a tooth), but it's an interesting lesson.

Terry Donohue
71 BMW 2002Ti 2.3
90 200TQ (2.0 bar)
95 BMW M3