[olddog]

Compression should be checked with all plugs pulled out and throttle wide open.

I thought 110 psi was low, but I didn't know what the compression ratio is or the cam. I figured if they were all nearly the same, then there is most likely no issue with the engine mechanically.

I never heard of a lifter staying pumped up after an engine cooled off and was restarted. I don't know everything, so let's assume it is for a minute. If the exhaust valve is lifted on the intake stroke, it is going to suck exhaust into the cylinder, not push fuel into the exhaust. With unaccounted for exhaust in the cylinder EFI will assume the proper amount of air is in it, resulting in a rich charge. On the compression stroke, if the exhaust valve is still lifted, it would then push some of the air fuel mixture into the exhaust. This could cause the back fire in the exhaust.

However if the valve is staying lifted off the seat, it will melt fairly quick. The exhaust valves cool by toughing the seat in the head. Also the compression will test low on that cylinder if the valve is leaking. Also a valve issue should pretty much be constant and the same at all temps.

If the plugs, wires, cap, and rotor don't find the problem. Do another compression check the proper way and see if they are all the same or if one cylinder is lower than the rest.

My guess, at this point, is that one of the cylinders is not firing intermittently and the unburned air fuel charge is shoved into the exhaust and lighting off in there. I suspect an ignition issue.