Poor running when weather is wet

[billc]

Hi, I have a 2000 Explorer with about 70k miles. Just recently it started to run rough and stall, but only when the weather is rainy and damp. It runs fine when it is warmed up, and in dry weather. I have replaced the ignition cables. Anybody have any thoughts?

Thanks in advance.

BillC

 

[dogfriend]

Hi, you didn't say which engine you have, but I'm guessing you may have the 4.0 SOHC. You may have a leaking intake manifold o-rings (gasket). When the engine is cold, the o-rings that seal the intake will leak and it will not idle very well. When the engine warms up, the o-rings expand and seal so it runs normally. The solution is to replace the intake manifold o-rings.

 

[BrooklynBay]

Do you have a check engine light? Did you scan the computer to see if there are any stored codes?

 

[Lizard]

Well ignition wires would've been my first guess. Maybe a long shot, but I'd check for a fireworks show at the wires. Find a nice dark area (not an enclosed garage..duh!!), and close your eyes for a few minutes to get them dark adapted then check under the hood. My wires are older and "leak" at any area where they come in contact with metal. You might try misting them with water from a spray bottle to see if you can recreate the problem. Check for arcing at the boots too. Did you use dielectric grease inside the boots? Maybe there is some contamination on the wires which is becoming more conductive under higher humidity. The water test should reveal this.
Also could be several wires running too close, (parallel) and are interacting with each other, more so in damp conditions.

 

[JDraper]

You also could have a cracked coil housing that causes the misfires when it gets too humid out.

 

[dogfriend]

Well ignition wires would've been my first guess.
.

Mine too, but he said he replaced them.

 

[billc]

The engine is the 4.0 OHV. The CEL came on back in Feb. and the dealer replaced the intake gaskets and o-rings. I replaced the ignition cables when this latest problem showed up about 2 weeks ago. I will try spraying some water around and see what happens. Thanks for your help.

 

[billc]

Solved, I think!

Well, after reading a bunch of stuff on this site, (thanks all) I crawled under the car with the garden hose and squirted water on the crankshaft position sensor and the EX began to stumble. I replaced it ($25) and squirted it again, no problem. We had a day of light rain the other day and I again had no problem. But I probably won't feel completely out of the woods until a monsoon comes through. Thanks everyone for your help.

 

[BrooklynBay]

Thanks for the update!