So one night I was doing 4th/5th gear pulls, got no knock all the way up to redline in 4th, but got a few flashes of the CEL in 5th after 8k RPM. I went home and got my laptop to datalog, and ended up getting between 50-100 knocks after 8k RPM in 5th but none in 4th. I retarded timing a little up top and also retarded timing a little just for 5th gear.
Did another pull and got the same result. Retarded a little more up top, one more pull and no more knock even in 5th. The next day the car started misfiring on cold start up but went away. By the end of the night on another cold start I got the code for cylinder 1 misfire.
I changed the plugs to the OEM iridium/platinum NGK ones about 37k miles ago so before I pulled those I swapped the coils on cylinders 1 and 2. Misfire still on cylinder 1. So I pulled the plugs and found these bad boys. From left to right are plugs from cylinders 1,2,3,4.
Before the night of the 4th/5th gear pulls I'd done several top end 5th gear pulls with no knock. Granted it's usually in warmer weather with more retarded timing as a result of IAT compensation. My question is what the hell started causing the knock? I'm guessing that the autoignition melted the plugs, rather than bad plugs causing the knock. But I'm not sure, can any one lend some insight?
Also I ended up doing a compression/leakdown test. Got 175-180 psi in all cylinders and an even 20% leak in all cylinders. The leakdown tester I used had 20% as within an acceptable range.
Did another pull and got the same result. Retarded a little more up top, one more pull and no more knock even in 5th. The next day the car started misfiring on cold start up but went away. By the end of the night on another cold start I got the code for cylinder 1 misfire.
I changed the plugs to the OEM iridium/platinum NGK ones about 37k miles ago so before I pulled those I swapped the coils on cylinders 1 and 2. Misfire still on cylinder 1. So I pulled the plugs and found these bad boys. From left to right are plugs from cylinders 1,2,3,4.
Before the night of the 4th/5th gear pulls I'd done several top end 5th gear pulls with no knock. Granted it's usually in warmer weather with more retarded timing as a result of IAT compensation. My question is what the hell started causing the knock? I'm guessing that the autoignition melted the plugs, rather than bad plugs causing the knock. But I'm not sure, can any one lend some insight?
Also I ended up doing a compression/leakdown test. Got 175-180 psi in all cylinders and an even 20% leak in all cylinders. The leakdown tester I used had 20% as within an acceptable range.
Misfire resolved but curious as to the cause
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