I don't have much experience with the LPG fueled engines, but I've seen where an injector sticks open, and will flood the cyc. with fuel.
This washes the rings, and drops compression, and of course, the super rich mix does not burn, so you get a misfire.
Wet plug and low compression were what I found. Added some oil, it brought compression up, but as soon as the engine was run, it misfired again.
Pulled the injector, swapped it with another, and the "bad" cyc moved...
Sonic cleaned all the injectors, and it "cured" the problem for that vehicle. If not, I was ready to replace the bad/stuck injector. (But upon pulling them, they were all filthy, so new fuel filter, sonic cleaned the injectors, keeping the bad one seperate so it did not get confused with the other 5 on this I6 engine.)
The coil and plug was fine, the valves and pistons were fine. Rings were fine, but washed with too much fuel, they don't seal up well at all.
I would imagine if you ran the engine at a high enough speed/RPM, that the right air fuel ratio would be reached, and the misfire would go away. (Depends on how stuck open the injector is.)
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