Temp related low boost

Matt twentyV matt_20v at yahoo.com
Mon Sep 19 11:59:24 EDT 2005

Tom, the ECU temperature sensor is mounted on the back
of the head under the throttle body.  Nothing I've
read suggests the ECU uses this data to reduce boost,
but who knows.  
If you have a VAGCOM on a laptop or ProDiag the sensor
temperature is available in the Block 0 data, you
could try monitoring it while driving and hit the low
boost condition.  You should typically see 90C +/-,
check the Bentley for correct readings.
The MFTS is just a off/on high temp. signal that
reduces boost and turns off AC.  Your test shows that
isn't the problem.

--- 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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