Re: Overboost protection, You have something wrong - Saab 9000 Bulletin Board - Saabnet.com
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Re: Overboost protection, You have something wrong
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Posted by jj (more from jj) on Thu, 3 May 2001 16:40:46 Share Post by Email
In Reply to: Overboost protection, Allan, Thu, 3 May 2001 16:21:27
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with your boost control system if you can hit the boost cut-off. You
should find out what is wrong with it and fix it, rather than use a
bleed valve to mask the problem.

The bleed valve would have to be inserted into the MAP sensor (Manifold
Absolute Pressure) line. This would fool the MAP into thinking there was
less boost than actual. This would in turn tell the Trionic ECU there was
less booost than actual and the ECU would alter fuel and timing to that
apparent level of boost. This would result in a lean fuel mixture and timing
such that the motor could detonate. Prolonged detonation will burn holes
in the pistons, not a good thing.

Your overboost problem could be caused by a couple of things.
You could have a split vacuum line that runs from the middle tap on the
BPC valve to the wastegate actuator. A leak in this line would not
allow the BPC to open the wategate thus resulting in high boost.

Another cause could be the BPC valve itself. Some people have had good
luck removing the valve, spraying the inside with penetrating oil and
slinging the valve around to distribute the oil. You may need a new valve.

You really should fix the problem, and not resort to a bleed valve.

jj
'95 Aero

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