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

Reply to
Zon
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In article , john@reply-to- group.please spouted forth into alt.autos.saab...

A couple of simple checks are.

1) is your gas cap loose. I think a lot of the more modern cars will show the check engine light but worth a look anyway. 2) Check your oil cap is on properly. Again simple free to do. 3) check for any vac hose leaks. A bit early for leaks to occur but a lose may have popped off or split. 4) Have you changed where you buy your fuel from recently? Different brand, or even different stations of the same brand can have fuel that behaves differently.
Reply to
MeatballTurbo

Checked. Gas cap was tight, and there is not check engine light on dash.

Checked. Seems to be ok.

Checked. All hose seem to be in proper place and also clamps are tight.

Nope. It is the same conoco premium gas I have been using since I bought this car.

Is there anything else I should check? It was doing just fine yesterday evening, so problem seems to be on-off kind of thing.

BR;Z

Reply to
Zon

BTW; what is correct idling speed? Just noticed that rpm gauge says 1000rpm when idling, which kind of sounds high. Is it ok for a saab?

BR;Z

Reply to
Zon

My old 900 I'm sure says something like 750 or 850 RPM (can't recall correctly).

But when on cold idle, or straight at the end of a run it will sit arround the 1k mark for a little while, then drop back.

Reply to
MeatballTurbo

Automatic or manual gearbox?

For manual I would say 850 (I thought I had a 9-3 manual but can't find it).

The problem sounds electrical. Engine management system?

If it helps muddle the waters. Charles

Reply to
Charles Christacopoulos

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