Date: Sat, 24 Aug 2002 21:25:59 +0100
From: "Lee Marshall" <leenopsamvespamenigma-it.com>
Subject: Re: My dealer hasn't got a clue, can you help? ('97 9000 Aero, Manual)


I had a conversation with the service manager yesterday. They did replace the exhaust systems and surprise (not) it didn't make a blind bit of difference. I mention the MAP sensor again but he said they had re-checked it and it's hose. Although I don't have too much faith in there ability to check anything. What you have said makes sense to me (and you would hope to Saab), I will keep on at them at let you know of the results. They have now promised to keep the car there until the problem is resolved. So (hopefully) I will have some more positive news within a couple of weeks. Thanks Lee "KeithG" <noonenopsamspring.com> wrote in message news:3D663C24.9010500nopsamspring.com... > Lee, > > That is what I meant. I would replace the short bit of hose or at least > determine that it is clear and does not collapse or is otherwise > problematic. Has the MAP sensor been tested to linearity or response > independently of the car to the 1.2 bar or so that the aero produces and > beyond to see what its response curve looks like? That is what I would > be interested in knowing. > > Well, 'under load' would be sensed as a throttle opening for a longer > period of time, more boost development, and a slower acceleration of the > engine speed. This would be a symptom of a bad ECU, I would think, but > that has been replaced with no change. I say ECU as it is not a sensed > value which would cause the overboost, but an algorithm. If the hose has > a split and opens up under sustained boost (possible scenario), the MAP > would see lower pressure and the ECU would keep the wastegate closed > looking for maximum boost and wild boost may be developed. > > I keep repeating this, but I am just an engineer and am supposing a lot > here. Basically, based on what has been replaced by the 'parts hangers', > I am leaning toward blaming the MAP, the nipple or its hose or possibly > wiring (map sensor ground reference), though I could be full of > pressurized hot air (as the Aero sometimes is!). One other thing, the > Throttle Position Sensor could, potentially, cause some problems though, > it is an outside chance. I would verify its operation and its ground > reference as well. I would guess that the system reads WOT from the TPS. > It then probably goes to all maximum power settings, maximum duration of > fuel injectors, maximum boost and opens the wastegate when it is reached > and when the RPMS increase to the point that it starts to taper back > boost. It sounds like it just ignores boost to me which leads me to > suspect the transducer. That you have no other drivability issues, does > not lead me to suspect the crank angle sensor (this should cue the ECU > to spool back boost as RPMS rise based on a calculation once again). > > based on my understanding (which may be lacking), if the boost is > uncontrolled, it should be the wastegate sticking (ruled out), the BPCV > sticking (3 different ones tried) or a bad pressure signal (not > completely ruled out) to the ECU. > > Good luck! > > KeithG --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.384 / Virus Database: 216 - Release Date: 21/08/2002

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