Re: plug gap and pinging - Saab General Bulletin Board - Saabnet.com


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Re: plug gap and pinging
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Posted by Ari [Email] (more from Ari) on Fri, 10 Jul 2009 07:46:06 Share Post by Email
In Reply to: plug gap and pinging, Mark from Toronto, Thu, 9 Jul 2009 11:42:54
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If the engine is pinging, the problem is waaaay past plug gap.

(1) use the plugs specified in the manual. If they are NGK, use NGK. Period. End of statement. The plug is an integral part of the knock-detection and avoidance system.
(2) gap the plugs per spec, slightly on the low side of nominal. Too wide a gap is the major reason for misfire. Spark plug gap opens with age.

The engine should NOT be pinging. There are a lot of very complex systems in the car to prevent this. However, the engine control only has so much it can adjust.

First and foremost - what octane fuel are you using? Does the problem go away with a higher grade of fuel? If so, use a higher grade of fuel. Detonation can destroy a turbo engine in very short order - this is an engine not designed to tolerate knock, because there are systems to avoid it.

The assumption is that the car hasn't been modified - nobody messed with the turbo or APC system to 'tweak' an extra 5 psi of boost, or otherwise mess with the system. I also assume you aren't seeing excessive amounts of boost (well into the red), indicating something has failed.

OK, say you're running 93 octane (US measurement system) and the engine is still knocking. Next question - is it really knock? Does it occur under heavy load and low RPM? Can you be sure it isn't something else you're hearing, such as a bad chain guide, lazy valve lifter, or wonky pulley?

If you've ruled out other noises, you're running the highest reasonable octane you can find, and the boost levels seem normal, then I have to assume you've got a pretty impressive carbon buildup in the cylinder, or something else to cause either increased compression and/or cylinder hotspot. I'd get the car to a dealer/indy mechanic with a Tech II scan device, and see if there are any knock codes. No, you won't see these with a regular OBDII tool from Auto Zone. I'd also consider removing the spark plugs and using an inspection mirror to examine the insides of the cylinders and head to look for excessive carbon buildup.

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