Re: set base boost - Saab 900 Bulletin Board - Saabnet.com
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Re: set base boost
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Posted by JohnK (more from JohnK) on Tue, 17 Feb 2004 09:09:21 Share Post by Email
In Reply to: Re: set base boost, John Roberts, Mon, 16 Feb 2004 16:06:54
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Most classic 900's need to have base boost reset. As noted, better spool up and max boost. Simple to test, since you have a gauge.

Boost taper happens but needle drop should be like 1/8" after sustained high rpm boost.

I hope you don't have Bosch platinum plugs, and do have the NGK BCP7EV platinums. Replace Bosch and regardless, regap, to 0.024. I have not heard any comments on your wires, but the ignition likes Bougicord and some have had good luck with Magnicore. Wires can make a big difference.

Once you verify base boost at 5+psi, I would then open your APC box and tweak the "F" pot about 90 degrees clockwise and bump the "P" pot about 30 degrees. You should get higher max boost with less taper. If the boost overruns early, cut back the "P" tweak until boost is smooth up to max, which is set by the "F" pot. Don't monkey with the "K" pot to preserve factory knock sensor protection.

There is a chance that your symptoms were caused by incorrect APC box tweaking to try to compensate for low base boost. That could produce the high boost overrun that cuts back to a reduced sustained max boost.

One other item. It's a good idea to periodically clean out your APC solenoid with carb spray and finish with a shot of WD-40. This simple bit of maintenance can solve lumpy boost performance.

posted by 208.208.152...

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