I've got an F-150 with a 4.2. I changed the alternator back in the spring, but ever since I did that, every time I go through a puddle (doesn't have to be deep) making a slight turn to the left, it starts missing, spitting a sputtering. I have had the alternator checked. It's good; changed wires and plugs - seemed to help. Battery light comes on and goes off after a while, like it is charging. I have inspected every thing closely and I don't see any issues. It only does the missing thing in gear and only after I go through water.
I have replaced the battery, plugs and wires again but the battery light sill keeps coming on and then going off after a few min. even when it's dry. The gauge shows a good battery charge and I have done a load test on it.
Could I get a little help?

 

I had a similar problem. 2002 4.2 runs fine until it gets some spray into the engine compartment. Afterward it misses a lot. The fix for mine turned out to be the coil pack which had a hairline crack in the resin filling the back of the coil pack. $78 & 20 min to fix.

 

Is the flexible splash guard in place down in front of the engine?