1990 Legacy wagon starts up, drives for about 30 minutes in rain or wet snow, then starts misfiring and dies. Will  start right back up, but acts as if not running on all cylinders. Tach all over the place but no power.  Can sit for awhile, then nurse it a couple more miles and it dies all over again.

Replaced spark plug wires, fuel pump.

Is there a crankshaft position sensor that could be getting wet?

Suggestions?    

coil pack??

it could be the coil pack  or the ignition relay(well hidden under the dash orange relay) or the igniter(under bonnet) Have you checked for codes?

 

TOONGA

Get it warmed up one night and most some water (spray bottle) on the coil pack, look for sparklies.

Get it warmed up one night and mist some water (spray bottle) on the coil pack, look for sparklies.

 

Do this ^   waiting until after dark makes the spark easier to see.

 

Also mist a little water around the spark plug end of the wires. If you used a cheap set of wires you could have one that is jumping spark to the block. I had that happen to me before on my 1990 EJ22 - it was so bad that I could see it in broad daylight! Had to wrap the boot with electrical tape to get to where I was going & get another set of wires. No more cheap wires for me!

 

the crank & cam sensors should not really be affected by moisture unless the housings are cracked/damaged (pretty rare)

 

Do you have a CEL on? (does it even work?) If so, finding out what the code is would be big help in diagnosing.

I had a similar problem with my 96 years ago and it was water getting into the MAF. I replaced the MAF and put the sound deadeners back in and it never happened again.

I had this problem (a while back) with a Datsun PickUp Truck... spark plug wires.

Spark plugs + wires or maybe a Cam Position sensor.

 

All 3 are easy to swap out to check.

You can actually take a hose with a light mist and work your way around the engine compartment. Also do it UNDER the engine too kaing sure to get the engine temp sensor wire, and the cam and crank position wires

Wire harness beside the battery in the fender well about 4 inch from fuse box is my gess broken or coroded wire