Re: Clicking sound when accel. - Saab 900 Bulletin Board - Saabnet.com
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Re: Clicking sound when accel.
Posted by MS (more from MS) on Wed, 7 Jul 2004 10:37:44
In Reply to: Clicking sound when accel., eee, Wed, 7 Jul 2004 06:04:57
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I'm surprised you can even hear the APC solenoid valve over the noise of the engine at the speeds you say you hear it. I could barely hear it at idle when I purposely triggerd it, and I never hear it under boost conditions even though I know it's working. If it is the APC "s" valve, the fact that it's clicking under boost conditions means that it is working as designed - keeping boost levels down because it senses engine knock/ping. Knock is not good for an engine as it causes valve/seat damage. Knock usually occurs with low octane fuel coupled with carbon buildup inside the combustion chamber plus hot ambient and engine temps. A hot day increases the intake temps which makes the already hot turbo boosted air that much hotter. The fuel is igniting before it is supposed to - called ping, or pre-ignition, aka knock. One of the APC sensors is a microphone attached to the engine and tuned to listen specifically for knock. When it hears it, the APC control box sends a signal to the solenoid to begin it's open/shut cycle (clicking) to lower boost levels (lowering combustion chamber temps), thus controlling fuel pre-ignition. Oftentimes a good overall tune-up takes care of knock. Techron fuel additive is also good for carbon buildup. A more efficient intercooler plus water injection is the ultimate knock-be-gone solution for turbo charged engines.
posted by 64.12.11...
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