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I don't know if this in any way helps, but I just started to have massive de cel popping, it started a week ago. after checking over all the rubber bits and suspecting everything else. Yesterday morning when I started it up the sound was not right. Running my hand around the headers found the problem. What looked like a small crack in the upper header. it was very hard to see. In fact it would have been under the small heat shield at the top of the head (which is no longer there)
I pulled it off and there was a small hole and a thin but long crack winding more than half way around the casting near to the header flanges.
it is out for welding today. I expect this will be the end of the popping.



Very useful info, Micah...when the ignition sensor failed, there was serious detonation going on inside the starboard side exhaust, to the point where a heat-shield weld failed on the silencer...I can't say for certain what caused the weld to fail, though.

We are on the same frequency though, as I planned to go over the intake and exhaust systems with HVAC smoke to see of there are any holes/leaks that were not apparent on visual check alone. Your input makes it more important for me to do so.