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Any particular year? Posted by Ari [Email] ![]() ![]() In Reply to: Re: Knock knock!, Buz, Mon, 23 May 2005 11:56:25 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The Saab turbocharging system (APC) has knock sensing. Depending on the year, it is a dedicated knock sensor, or knock is detected by the DI cassette.
When the APC system detects knock, it will reduce boost. It can dial boost all the way from full boost (boost needle all the way to the end of the yellow/beginning of red) to Base Boost - about mid yellow on the boost gauge.
When you get knock, how much boost are you pulling? If you have knock and the boost gauge is going all the way to Full, then there may be a problem with the APC/BPC solenoid (name depends on year). If you are stuck at Base Boost - mid yellow - and still getting knock - then the APC system has done all it can - it has dialed back boost as much as possible. If the engine is still knocking, there is a problem.
The Base Boost level was designed to allow the engine to run without knock, with low octane (87 or so) gas. But that's a normal engine. If your compression ratio has been increased - either due to engine modifications or carbon buildup in the cylinders - then it may still knock on 87 octane fuel even at base boost. If you're running with too hot a spark plug, or you're running lean, that will also encourage boost.
So - some questions-
What Year? There were differences in different years.
What octane gas? Have you tried higher octane fuel?
Where is the boost gauge running?
Has the car been modified in any way? Anyone adjusted the Base Boost level to try and compensate for other problems?
How do the spark plugs look? Are you running rich or lean?
Any known problems with the car - Check Engine light on, etc?
posted by 192.249....
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