Date: Fri, 23 Aug 2002 09:44:04 -0400
From: KeithG <noonenopsamspring.com>
Subject: Re: My dealer hasn't got a clue, can you help? ('97 9000 Aero, Manual)
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 Basically, based on what has been replaced by the 'parts hangers',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
Lee Marshall wrote:
> Keith,
>
> If you had said that the Pressure Transducer was also known as the MAP
> sensor I would have known what you were talking about! According to County
> Saab, they have already checked out the MAP sensor, at least that's what
> they said when I asked them about it a few months ago. I will bring this up
> with them again later today. Is there a chance that a fuel or waste deposit
> could have blocked the nipple or hose to the MAP sensor?
>
> You said that you assume that I have not driven another Aero that works
> correctly. True, but I did drive mine whilst it worked correctly (I have had
> the vehicle for 2 years).
>
> One bit of confusion I do want to sort out is that I believe the problem
> only happens when the engine is under load, I don't believe it is related to
> the throttle position. My reasoning is that the problem never occurs in
> first gear and very rarely in second, when there is little load on the
> engine. However the problem is very prevalent in fifth and occurs often
> before WOT. When the car is in third or fourth, it requires WOT to instigate
> the problem (usually on a country road when you are trying to overtake a
> line of slow moving traffic!!!).
>
> Thanks for you help so far Keith!
>
> Lee
>
>
>
> "KeithG" <noonenopsamspring.com> wrote in message
> news:3D64E32C.5010809nopsamspring.com...
>
>>Lee,
>>
>>Still more musing on my part... If the MAP sensor lost a ground
>>reference, I could imagine it exhibiting the symptom you describe. Why
>>it does it only at WOT confuses it a bit. I am assuming that you have
>>not driven another Aero which 'works correctly' to have a feel for it. I
>>would disconnect the ECU and MAP and take a volt meter to verify that
>>both the ECU and MAP get a low impedance connection to ground. If there
>>is any variation, clean the bog engine ground cable at both ends and the
>>ground connection for the FI system. It should be a single bolt with a
>>number of ring connectors. To find this ground point, you'd have to have
>>the electrical manual, guess, or ask the technician. It'll probably be
>>near the battery or on the engine block somewhere. It COULD (very
>>outside chance) be something INSIDE the short section of tubing or the
>>nipple on the intake manifold which plugs the port and causes pressure
>>to be under reported as well. If all these check out, swap in a known
>>good MAP and see what it does. Please let us know what you learn as this
>>is now bugging me.
>>
>>KeithG
>
>
>
>
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