Date: Wed, 7 Apr 2004 16:03:54 -0600
From: "Zon" <johnnospamy-to-group.please>
Subject: How to diagnose the cause of loss of boost pressure?

I'm experiencing loss of boost pressure with my '99 9-3 FPT. Nowadays boost gauge goes up to normal figures very rarely. Most of time It barely reaches mid yellow area, even in higher gears. Not long time ago, boost gauge went little bit to red area in all gears from 2nd to 5th. After reading various web-sites and forums, I have come to conclusion that there are quite a few things that can be wrong. Could it be air flow (or mass) meter (is that also called MAF?), by-pass valve or magnetic boost control valve (is that also called APC?) Can you tell me the procedure to diagnose those? I'm used to work on cars, but not turbo boosted cars, so these questions may sound somewhat naive. I'm sorry If they do. What I have found about these so far: 1. Air flow meter: Can be dirty or broken. I have understood that in some cars you can measure a voltage somewhere and get an idea of air flow meter function. Can I do this with my Saab? How? 2. By-pass valve: I have understood that a small hose controls the valve. If I disconnect this hose, what should happen? Full boost, or no boost? If I blow into or suck from this hose connector, what should happen? 3. Magnetic valve: I have understood that the wires that go to the control use PWM, so not easily measurable with regular voltage meter. However, there are those three small hose that go there: I do not quite understand purpose of them. What do they do, and could I use them to diagnose if valve works or not? I'd appreciate some help, and I also would like to hear also your ideas of what is causing this? Car seems to work fine, no abnormal noises, sounds or warning lights. It just feels weaker than before, and boost gauge shows smaller boost. BR, Z

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