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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