I have been fighting this problem where my 87 GT 5-speed will not start or run when it's wet (rain or humidity). So far I have replaced the connectors on top of the coil, dist cap, rotor, and plug wires. I started it today and misted the coil with water and it would not die, the thing was soaking wet by the time I was done and still running. It's a bit frustrating since I figured that was the culprit. Any help would be greatly appreciated.

Does the fuel pump still turn on when its raining outside? Or if you're not sure check the relays and make sure they are up right and not upside down to collect water. Does it just turn over? Or attempt to fire at all? When you get a chance have the vehicle running and wash certain spots with the hose where you would have constant water dripping or running instead of a mister ofcoarse avoiding crucial areas of the engine to avoid more problems. Or try washing your car running and see if that might trigger it to die out. I've seen starters fill with water also or the solenoid if it runs and than wont turn over. Water is everyones closest needing thing and pulling your hair out kinda like women

Fuel pump runs fine. Motor turns over, just won't fire. Car will start after a light rain or car wash. Problem occurs mostly after a hard rain, while driving down a wet road, or when it is overly humid out. I thought I had it figured out a couple times but then it comes back to stump me again. As soon as it dries out enough, it will run like a champ.

that problem is GENERALLY a cracked coil. remove and inspect the coil for any cracks. just misting it might not work. If you have another coil without needing to buy one, just insert it. and give it a try! or if you can get one cheap enough :P

I agree with the coil or ICM connectors being the most likely culprit. If that doesn't solve the issue...
When it won't start, pull electrical connectors apart to verify for water. if water is found, check for deterioration of the water seal on the back side and front side. Adding Dielectric grease may fix it temporarily.

Had an old Ford Ranger (1982 V6 4x4) that would not start when it rained. I added dielectric grease to the coil and ignition connectors and it solved the issue for about a year or so.
Then I swapped the ignition for a GM system.

-Dave

[This message has been edited by IFLYR22 (edited 06-09-2011).]

check the bulkhead by the battery that big brick with the bolt in it. that houses the ignition power... try cleaning it with a toothbrush and some baking soda/water solution. then use dielectric grease to pack it

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1985 gt notchie auto (pic)| 3800 SFI N/A coming soon
1986 se notchie standard 4spd | 5.3 vortec soon

Thanks for the ideas, I'm going to pull the coil off my 86 this weekend and see if that fixes it. No rain in the forecast though...oh well, motor does need a good cleaning

When it acts up -won't start- try this, thing is, you need the car to be in dark place or at night. Have somene crank and watch the coil and other ingition parts, wires, coil to distrib park wire, etc and see if sparks are jumping from them to ground. You may simply have a bad/corroded ingition related connector, reseat all of them a few times each -that may clean the contacts enough to let it run- , base of distrib, coil etc/ Good luck. Oh yeah the tach should move when cranking, if not you dont have ignition pulses, here again, likley a bad connector. These cars are quite old now and old things corrode, go bald and get lots of wrinkes, oh thats me.

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Well, I took the coil out of my 86 and put it in the 87, hosed it down good with the garden hose and it started right up. Drove through a torrential downpour today and it ran like a champ. Looks like it was the coil, going to pick up a new one later this week and keep the old one from the 86 in the trunk as a spare.

You didn't mention anything about the spark plugs themselves.

It could be coil, wiring connectors, moisture inside the cap or bad spark plug wires. Start it up in the dark and see if you see any sparks...might even try spraying some water on wires from a hand pump bottle. My guess is you will see a real nice light show. If you see it, replace as necessary.

As far as the plugs go, I'm going off of what the previous owner told me that they are new within 6000 miles. Pulled the 3 on the trunk side of the motor and they looked good. Probably should have replaced them but those in the back are such a pain.

It's been running good now so I'm pretty sure I've got it fixed. Thanks everyone for the help!