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Re: '91 9000 Engine management
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 19 Apr 2005 13:41:04 Share Post by Email
In Reply to: '91 9000 Engine management, Everett [Profile/Gallery] , Tue, 19 Apr 2005 12:39:31
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A 9000Turbo with the 2.3L it is running LH2.4.2, DI/APC. Trionic didn't show up until '93, I believe.

You are having a Base Boost issue. If the engine control (APC) thinks all is well, it allows full boost - to the end of the yellow/beginning of the red. If it detects knock, adjusts the BPC valve (mounted on the radiator, three hoses, one electrical connector) to feed more pressure to the wastegate. The wastegate opens sooner, and boost is reduced to 'base boost', around mid-yellow.

Do a search on Base Boost. Tons of information. But basically, one of three things is going on - either you are knocking and the APC is doing it's job, the APC *thinks* your engine is knocking, or (3) something is busted.

If you are knocking, try running higher octane fuel if you aren't already running the higest you can find. If that fixes it, you may be stuck with high octane fuel, but also check spark plug gap, spark plug heat range, and other things that can cause knock, like running lean. Or years of carbon buildup have created hot spots and increased cylinder compression. Don't overlook lean running.

Thinking it's knocking? Sounds that imitate knock can fool the knock sensor. Examples would be a really shot wheel bearing or bad engine mounts.

Something busted? A typical example is a bad BPC valve. They usually fail 'safe', which would be to base boost.

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