Temp related low boost

[Taka Mizutani]

Tom-
I experienced pretty much the exact same issue, with similar results-
I don't know if your car is chipped or not, but anyway....
 With Lehmann stage I chipset, I would normally see 17psi with 19psi
on 4th and 5th gear extended pulls. When I had an issue, I would see
full boost until the engine was warmed up, then I would see a peak of
12psi with a very slow increase in boost to even achieve the 12psi.
 I replaced the MTFS, the ECU temp sensor on the back of the head, the
plugs, plug wires, distributor cap and rotor, still no success. Finally, I 
found
out from my mechanic that the altitude sensor had failed- I don't really 
understand
how this failure seemed to correlate with temperature of the engine, but it 
did.
 After replacing the altitude sensor, I never saw the problem recur. It's a 
rather odd
thing, never documented by SJM Autotechnik, or in the Bentley, but that 
worked for
me. I would go through the usual checks (VAG-COM is very useful to see what 
your
ECU values are cold and hot) in the Bentley before doing this.
 Taka


 On 9/19/05, Tom Ellis <tom at tomellisphoto.com> wrote: 
> 
> Alright folks, here is one that I hope you can help me with. For the past
> month or so I've noticed that my boost is limited to 1.4 bar once the 
> engine
> temperature (as shown by the coolant temp gauge) gets above a certain 
> point.
> On the temp gauge this seems to be at the thin line halfway to the first
> thick line, where that thick line is normal operating temperature. At
> coolant temps below the "thin line" I get full boost to 1.8 bar.
> 
> This does not seem to correlate to oil temperature. Driving on the freeway
> on a cool evening with the coolant gauge showing a temp at or below the
> "thin line" and oil temps somewhere between 60 C and the next mark on the
> oil temp gauge, I get full 1.8 bar no problem. But once the coolant temp
> rises above that magic line (regardless of oil temp) maximum boost drops 
> off
> immediately to 1.4 bar.
> 
> I've looked in the archives and found a reference to a possible problem 
> with
> the MFTS that might cause these symptoms. So I disconnected the MTFS and
> drove the car - same results.
> 
> Any ideas? Is there some other coolant temp sensor that I don't know about
> that could be the culprit?
> 
> Thanks for any suggestions!
> 
> Tom Ellis
> 
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