I have an '03 GC w/ 175Kmiles. A few months ago while my wife was driving during a rain shower the van began to misfire and began running on a limp home mode. I retrieved the van about 20 minutes later. It ran fine, and the only code it showed was a bank 1 lean or rich (don't remember which one, and did not write down code number). Cleared the code and all was fine.
In late October it began misfiring again during a rain shower. It flashed a P0304 code. I diagnosed the problem as a bad coil - coil replaced.
Last week during a snow/rain storm it began misfiring. I was able to detect some arcing from one of the plug wires - wires replaced.
Today during a heavy rainstorm it began to misfire again and went into limp home mode. The only code I got was P0455 (evap leak), which I cleared (this code has been persistent throughout the year). I drove it over 60 miles while it misfired and it would not throw any code. While misfiring this time I could hear backfiring through the intake manifold. FYI - the plugs have about 25K miles (Autolite double plats) on them.
I'm out of ideas on solving this - anyone run into something similar?

 

Did you say all the wires are new? If not, they should be at that high mileage.

 

Yes, all wires were replaced.

 

maybe a faulty crank sensor ?

 

My brother was thinking the same thing. I will try that.

 

Also could have a bad flex plate, if the crank sensor doesn't fix the problem.