[jeffcoslacker]

Originally Posted by cadgear

The placement of the ICM was kinda a bad idea, being right in front. There you have rain coming in via radiator, roadsplash, and anything else that water can think of. I once drove through SHALLOW water (not even half an inch) and enough splashed up on the ICM to kill the car for a minute. I appreciate GM's later idea to move them to the back of the engine, though if you have bad ws at the firewall end of the hood similar could happen.

These coils will fire across a 1/2" gap if allowed, so the gap is NOT the problem. I agree there is most likely a cracked insulator on one plug. Very common mistake if you are not someone who does this stuff daily. Might want to investigate the condition of the module, and the coils' connections to it also, given the no-start in rain you mentioned. You might try misting water from a spray bottle near the ends of the plug wires while running, to see if you can cause a misfire, then you'd know which plug was the problem.