Re: Help with chattering APC Relay? - Saab 900 Bulletin Board - Saabnet.com
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Re: Help with chattering APC Relay?
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Posted by Bill S. [Email] (more from Bill S.) on Mon, 11 Oct 2004 21:42:06 Share Post by Email
In Reply to: Help with chattering APC Relay?, vsfoxe [Profile/Gallery] , Mon, 11 Oct 2004 16:13:24
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Do your brake lights work?

The red/white, red and white wires are for your brake lights. The small white wire coming from the switch tells the APC controller when the brakes are applied. When the brakes are applied, the APC controller stops powering the APC solenoid (so your car reverts to base boost), which explains why stepping on the brake stops the chattering.

It sounds like your APC controller is trying to modulate your boost, thinking that it's too high. When the APC controller detects knocking, for example, it modulates the APC solenoid to reduce your boost - you don't hear it cuz you're too busy hanging on and grinning!

When you say "APC relay", you mean the APC solenoid, right? I don't think there is any such thing as an APC relay.

If your knock sensor is telling the APC controller that the engine's knocking it will make the solenoid chatter. Could be the knock sensor's sending a bad signal - could it be that your engine's running lean when cold and actually is knocking? Doesn't seem likely as it seems your engine'd be too cold to pre-ignite, but it might not be a problem with your APC system at all. What do your plugs look like?


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