runs poorly / misfires, during and after torrential downpour

A brief bit of history first. 2001 / 3.8. Quickly power washed engine for convenience sake, ran poorly for an hour or so until it dried out, then replaced the isolator bolts back in June (?) or so. Passed provincial e test shortly thereafter with apparent ease. Ran like gangbusters ever since, although mostly it's been relatively dry weather here except for the odd regular rainfall, even then it ran equally fine. Had the cowling off to do the iso bolts, and noticed that the 'fit' was not super tight upon replacement. There was a little concern on my part that the fit could be a tiny bit better, but just chocked it up to repeated removal (was off at least once before to replace wiper motor) and general wear on the plastic clips etc, notably where it meets the bottom of the windshield area. Close but not what I would describe as absolutely watertight. Also I'm assuming that the spark plugs, wire, and coil are all factory original (138,000 mi). Maybe I'm foolish, but my basic contention is .. if it ain't broke don't fix it. Plus I'm on a low financial budget overall. Ok, hope that's sufficient history ...

Yesterday there was a torrential and I mean TORRENTIAL downpour while I was driving at hwy speeds. I imagine there was lots of tire spray and perhaps some water leakage at the cowl. Yeah, it immediately started to run like a bag. Eventually got home, opened the hood and sure enough there was evidence of water, still laying in the crevices of the plenum upper half. Left hood open to allow evaporation. Drove a few hours later after the rain had subsided, and it still ran like a bag. Haven't checked it today. Even still, I'm looking for advice on what to check, replace as possibly the most likely cause - coil? wires? or ???. I do have a spare used coil that could be swapped out. Just wondering, if anyone has advice on where to look or what part(s) to suspect first of all. All recommendations are appreciated.

Thanks.

ETA: CEL is not on

Coil getting soaked maybe? Since it has rained hard lately, the Windstars have a funny design to channel rain water away from the front windshield. The cowl collects the rain water and it channels to the middle of the cowl right over the back of the engine. It has a plastic tube that resmbles a gutter type design that directs the rain water thru the firewall and down between the transalxe and rack and pinion on to the ground.

This plastic gutter has an elbow the leaks thru the seal and this makes the rain water fall right on top of the Plenum and Coil area, this could be making the Coil short to ground. Look for signs of water or rust at the base of the Coil preventing the Coil from making a good ground to the engine block.

On my van the seal had deteriorated and all rain water collected was over flowing thru the back of the engine.

Yours might be doing the same and messing up the Coil, Fuel Injectors or PCM wiring... worth taking a good look back there.

Two possibilities and my 2001 Windstar has experienced both:
1) There is a tech bulletin about resealing the cowl/s for water entering the PCM area. I use about one-half tube of Permatex 24105 every time I've had to remove the cowl/s. This happened to my Windstar at 46K miles and the PCM eventually failed at 160K miles.
TSB 05-23-7, superceded 06-14-10

2) Check the under hood battery box for water entry. If the lid isn't snapped in place water can run down into the base of the PCM power relay. My PCM didn't like the resulting 8.2 volts, and this along with the earlier (46K miles) water entry, resulted in the
original PCM's death.

btw - Don't forget to check the downspout per Ed's suggestion above...

Great, that sounds like excellent advice. I'll admit though, I still haven't looked at the problem any further. Yet.

I've only driven the van a few times since then, the weather was dry each time, and it ran absolutely fine. So, the urgency level just hasn't been high enough to motivate me. I'll certainly take the info into consideration when I finally get around to having a peek and a go at it, which should be soon.

Will probably post again with my findings, for the sake of posterity.
Thanks again for the advice.

I just had roughly the same issue but after i put my winter tires on the van (i don't know it "Felt Funny") and after i got home the van sat for a little while then i had to run out so after the van warmed up the van started to feel like it had a misfire but never had the issue before so i thought maybe it was like the focus i had and had traction control where one tire might be bigger than the other so i put my summers back on and the issue seemed to persist( Never did this till i changed the tires). so when i went back out the van felt like it had a misfire at idle in gear but as soon as i put it in neutral it went away so now i am thinking maybe it's trans issues.... so i went the cheaper route and bought a coil pack, plugs,wires and replaced them all and after i finished i looked at the coil pack and it had the dreaded cracks in the backside of it so i guess it was a misfire, plugs looked like they were firing ok and that just left the wires that were motorcraft so they were all originals plugs,wires,coil w/135000km on them. so i took the van out again did a 30km drive around the city and found no issue with a misfire. i guess the van lives till another day, if it were trans issues i would have scrapped it. but it just seemed funny that one day it ran fine the next ran like crap, both days were dry and sunny. so i wasn't sure what the issue was as i had no CEL but i still had 4 sensors that won't reset after 2 months of driving with a full tank of fuel

An old Windex t bottle filled with water on a dry day might help you find the problem. Just spray on each suspected cause until the problem shows its face. I'd start with plug wires and the coil.

i changed all that and it cleared up the surging power issue i just have 3 sensors that WILL NOT and i repeat WILL NOT reset...... i guess i am changing o2 sensors this weekend and see if that helps...... i have no codes but the 4 sensors have yet to reset after i insured it in august 2014 and to this day still blink when i hook up my scanner i just hate throwing money at something but if i had the choice of car or wife i choose the car it is cheaper in the long run and can't divorce me and get half

I'm confused by your description.... my scanner doesn't "blink" when sensors don't "reset". The way my scanner works, when the MIL is reset a new code is set (non-MIL), telling the technician that the monitors have not yet reset. When I read the monitor status, it shows the list with an indication ("OK") next to the ones that have completed or not completed ("Pend"). If there is a sensor problem, I think it eventually sets a corresponding code.

I've noticed that the catalyst monitor can take a while to complete, mainly because it requires a specific driving condition that isn't easily met in a lot of driving circumstances... the condition is not met in normal stop-and-go driving or highway speed driving. I'd have to look it up to see exactly how the condition is described, but it's something like cruising at 40 mph with steady throttle applied (no coasting, no acceleration) for 40 seconds.

Regarding oxygen sensors, the Windstar has four, two that monitor the engine exhaust (one on each bank) to set the fuel trims, and two that monitor the catalytic converter exhaust to make sure the converters are correctly functioning. If an O2 sensor goes bad (i.e. bad heater or bad O2 signal) the PCM will detect this and set a code, describing the nature of the failure and the sensor involved (e.g. "heater open ckt").

My scanner is an older one Innova 3030 scanner when the sensors are set the indicators on the top stop flashing and the ones that still need to set will flash telling you that you have sensors that still need setting it just so happens that these (4) will not set even after 4 months on driving in the city several times on the highway and i even tried to reset the pcm by clearing the codes again.

I still have 0/0 codes and i have a yellow light for emissions due to the:
C=Catalyst Monitor
EV=Evaporative System Monitor
O=Oxygen Sensor Monitor
OH=Oxygen Sensor Heater Monitor

These sensors won't reset so i am thinking maybe i'll replace the O2 Sensors maybe that will clear them up (Darn FORD'S Anyways:sarcasmsign:)