Date: 7 May 2002 18:02:01 GMT
From: davehinznopsamcop.net
Subject: Re: My dealer hasn't got a clue, can you help? ('97 9000 Aero, Manual)
Someone who looks an awful lot like Lee Marshall <leenopsamamenigma-it.com> wrote:
> They replaced the wastegate before the turbo (they thought it might be
> jammed).
OK, good, that's where I would have started.
> If the knock sensor was bad wouldn't that affect other areas of the
> engine like starting and emissions? Apart from replacing the sensor,
> how else could you tell if it was faulty?
Disclaimer: I don't know the inner workings of your particular control
unit.
However - as I understand it, and I'd be surprised to find that it has
changed, the knock sensor is there specifically to let the system know
when it's boost has gone so high as to cause predetonation (ping), and
to back down on the boost from there. Look at it this way - your problem is
that your boost is too high, right?
The only way for boost to be controlled is by opening the wastegate,
ultimately. If the wastegate isn't opening, it's either a problem
with the wastegate itself (which has been changed), or with the parts
that are supposed to be opening it. So, either the control module is
telling it to open and something between it and the wastegate is bad
(solenoid, right?), or the unit is bad, or the unit is getting bad
input from a sensor which is supposed to modulate boost.
I've been to that dealer in Milton Keynes, but it was about a decade ago.
(the new 900 was just coming out, I found myself in England for a few
months, and went in there to ask the sales guy to arrange a factory
visit in Trollhatten). They seemed quite knowledgeable about the cars
at the time, so I am a bit reluctant to second-guess them. However,
it wouldn't hurt to ask if they've narrowed it down to a sensor, or
a control problem. Either the box isn't getting the right information,
or it is, and it's actions aren't being translated into opening of the
wastegate. Until they can tell you which side of the box the problem
is on, any fix will be by blind luck.
> Thanks for your prompt reply, keep them coming!
Please note previous disclaimer; my in-depth understanding of the
Saab's boost strategies is based on the APC system which I believe
predates your car. But, the principles remain...
> Lee
Dave Hinz
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