Re: 92 9ooo turbo boost mystery... long - Saab 9000 Bulletin Board - Saabnet.com
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Re: 92 9ooo turbo boost mystery... long
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Mon, 22 Nov 2010 14:09:41 Share Post by Email
In Reply to: 92 9ooo turbo boost mystery... long, john m, Sat, 20 Nov 2010 19:54:03
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The boost gauge is going to the max - for a normal engine, it should NOT go into the red. Base boost is mid yellow. So you're getting full boost. There is no problem with the wastegate. But all the boost gauge shows is intake manifold pressure. That means you're getting the air, but it takes more to make power - fuel and spark.

The implication is that you see the gauge go to the end of yellow, but sometime the car moves out, and sometimes it's doggy.

First is RPM - At low RPM (2000-3000) you can get plenty of boost, but the engine can be a little doggy. Above 3K it should take off.

One option is that you're getting some knock. Unlike older cars, when the system detects knock, dialing back boost is the last thing it does. Before that it retards the spark, something it can do because this is a DI-equipped car. This results in less power. Knock can be very finicky, down to things like how warm the engine is, outside air temperature, and engine speed.

Even with plenty of air and properly timed spark, if you have poor fuel delivery, the engine will run very lean, and the spark will retard to prevent knock. This is less likely, but still possible.

I would check your plugs - make sure you have the exact right NGKs (no substitutions!), gapped properly (see the decal under the hood). I assume you have a red DI, not the later black DI cassettes. If the plugs are old and worn, or have a nasty build-up on them, replace them.

Lastly, if you're not running high octane fuel, try running one step up (89 instead of 87, 93 instead of 89, assuming you're in the US). See if that helps.

But if the boost gauge is going to the end of red, the turbo and wastegate are working properly.

posted by 75.11.5...


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