Truck won't run in the rain

2002 2.7 AT 4x4.

The last few days when I try to start my truck during or after a good rain, it will start right at first then stutter and die when I put it in gear. When it stutters, the lights on the dash are blinking on and off. It doesn't so much feel like it's not getting fuel/spark as it feels like a loose ground or wire connection or an electrical short of some kind. Reading codes after it stalls gives no codes.

When I let the truck sit and dry out after a rain it starts and runs perfectly. This leads me to believe the problem is not water getting in the gas - because water would stay in the gas even after it stopped raining and continue to cause the problem.

Looking under the hood, there is no sign of moisture even while it's raining out. This morning I removed the cowl at the top of the hood, and that space appears to be draining properly. I also accessed the plugs to the ECU and it was dry all around them, no sign of water entry. No water on passenger side floor.

I'm wondering if anybody else has ideas for where I can check for electrical connections or grounds that could be getting wet in the rain and causing this problem? Or other ideas of what might cause it?

 

Spark, fuel, air... when she is acting up pull a plug and leave the coil attached and ground the elctrode and check for spark. If there is no spark at least you have a direction to start your diagnosis. If there is spark, take your test light and check for constant power at one side of the injector and on the other side crank the motor over, the test light should pulse, if it doesnt I would look at your crank and cam sensor. Pop the air filter out... I have seen where a paper air filter would get saturated with water on it and not allow air to pass through.

Does she have a tachometer, is so, does the tach needle wiggle during cranking? While this is not a definative test for a crank sensor issue it is an indicator.

When you pull the spark plug, sniff it for fuel smell.

The other thing is the wiggle test, locate the various connectors for the ignitor, cam/crank sensor, engine coolant temp sensor etc and have someone crank the motor for 5 seconds while you wiggle each connector and see if she starts. Dont grind on the starter for too long without a cool off period for the starter or you will be putting a starter in it too.

 

what does the inside of the airbox look like?