My dad has a 02 f150 with the 4.2L v6. After raining or after goin through the car wash it feels like the motor has a really bad misfire. But after about 30 min (I'm guess whatever was wet, dried) everything is running Just fine. To me it seems like maybe some water is running off of the cowl and dripping onto one of the ignition coils? Any ideas of help is greatly appreciated.
Thanks
Chris

 

Get yourself a 99 cent spray bottle from walmart. go outside after dark and spray all your plug wires(with all lights off). I'm guessing you will start to see arking from your plug wires onto somewhere on the engine. Check for rubbing on the manifolds or head. Water is a sign of an ignition concern. could be a cracked coil as well, clean the coil surfaces and check for hairline cracks in the yellowish surface of the coil.

 

Thanks for the help! I'll try this and see what happens

 

That's what happened. Get some dielectric grease and put a good amount in all of your plug boots.