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 Basically, based on what has been replaced by the 'parts hangers',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
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