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Re: 84 900 T knock
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Fri, 9 Nov 2007 06:02:05 Share Post by Email
In Reply to: 84 900 T knock, Trollguy, Thu, 8 Nov 2007 19:30:38
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The APC system dials back boost when it detects knock. But it only dials back to base boost - it can 'dial back' no farther. It sounds like you're knocking well before that.

Question 1 - what timing are you running? Check the timing and make sure it is set to the decal under the hood. Running too advanced will cause knock.
Question 2 - what gas are you running? Try running a higher octane gas, if you aren't already running as high as you can reasonably find.
Question 3 - spark plugs - how do they look? What kind of shape are they in? Do they look white? Make sure you have the right plugs, gapped per the manual (again, see the decal). Don't run a hotter plug than stock if you don't have to.
Question 4 - how did the plugs look? Where they a stark white? That indicates lean running, which will contribute to knock. check for vacuum leaks, make sure your fuel pressure regulator (FPR) is working, and check for more vacuum leaks.

When the plugs are out, peek into the cylinders with a flashlight. What does the top of the piston look like? Can you see it, or is it a black mass? If you've built up a lot of carbon in the cylinder, that increases the compression ratio, which causes knock. Short of pulling the head and de-carboning the pistons and head, you may need to run the timing more retarded.



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