Originally Posted By: meep
There's another possibility we haven't covered--- predet due to carbon buildup or a hotspot such as a poorly seated exh valve. That would do exactly whats listed above and could be informally tested by a tank of 93 octane....
I have seen lots of this (carbon knock) in our fleet trucks when they get very high mileage. A dose of kreen in the gas clears it right up. Most times they make a noise similar to piston slap when first started cold when it builds up a bit...
There's another possibility we haven't covered--- predet due to carbon buildup or a hotspot such as a poorly seated exh valve. That would do exactly whats listed above and could be informally tested by a tank of 93 octane....
I have seen lots of this (carbon knock) in our fleet trucks when they get very high mileage. A dose of kreen in the gas clears it right up. Most times they make a noise similar to piston slap when first started cold when it builds up a bit...