Originally Posted by john_galt

I've changed my mind. I don't think it is a head gasket issue. It now looks like I had two separate problems.

I removed the rear heater lines from the coolant system. Now, the pressure holds overnight, even with the #2 spark plug removed. I saw no coolant in the cylinder the next day (borescope) and turned it over with a rag over the cylinder. Seemed like only fuel came out - no coolant.

The P302 has become increasingly regular. After a new front O2 (seemed biased lean), cleaning the IAC valve & throttle body, I saw no changes to the misfire - though it does run better.

Compression is: (1,3,5) 203, 205, 210 and (2,4,6) 205, 210, 220. My current thought is that it is a fuel related misfire, probably a dirty fuel injector.

If it were fuel pressure, I'd think the misfire would move cylinders and perhaps be towards the return of the fuel rail on the passenger side. Thoughts?

I'm just started a tank with Lucas Fuel System cleaner. We'll see.