rough running when damp

[freak]

My 2000 XLS 4.0 OHV explorer runs extremely rough once in a while when the temperature has a wide swing and humidity condensates. I know that moisture effects ignition wires/plugs/coils. When this happens the engine will run rough till it warms up and dries out the engine. Maybe 5-10 minutes. The engine runs very well otherwise. I've looked around and can't see anything obvious. Is there any specific area that explorers and known to have problems with moisture and the ignition system?

 

[Robman]

My 2000 sport 4.0L OHV 5speed was doing this in damp weather and would also develop a miss in the rain.

A spark plug boot had a crack in it.

I changed the wires, plugs and just for good measure replaced a inner fender skirt thingy which was ripped, and all is well now.

 

[Mike65]

My 2000 sport 4.0L OHV 5speed was doing this in damp weather and would also develop a miss in the rain.

A spark plug boot had a crack in it.

I changed the wires, plugs.

X2. That was my first thought on your problem too.

 

[Runnin'OnEmpty]

You might also clean the dirt and grime off the top of
the coil pack. The gunk absorbs moisture and could
cause arcing and voltage loss between the terminals.

 

[J_C]

I also had a similar problem which was fixed with new plugs and wires, though I think my problem was compounded by the fact that it wasn't a daily driver and so the battery had some time to drain between uses then with short trips, I was always running on a partially charged battery.

When I swapped the plugs and wires I didn't notice anything wrong with them, sure there was a little soot buildup on the plugs but nothing obvious yet the problem disappeared once they were swapped. Some people say it's important to also clean the rust off under the coil pack, but I didn't do that, still question, disagree with the theory some have proposed that it might be an important electrical ground (besides the one theory I read that seemed reasonable which was that there might be a grounded metal cage around the base that reduces RF emissions getting into the radio, but not all vehicles have their coil pack mounted on any metal.

 

[Robman]

I had also taken the coil pack off and cleaned it up but it made no difference, the plugs and wires were the remedy. It's a good idea to clean it up though.

 

[freak]

The problem is it's so intermittent, depending on the weather. Maybe I'll use the garden host to troubleshoot it.

 

[freak]

You might also clean the dirt and grime off the top of
the coil pack. The gunk absorbs moisture and could
cause arcing and voltage loss between the terminals.

Well it happened again so I waited till dark and went out with my daughter to start it again. It still wouldn't start and I could see arcing all over the top of the coil pack. I sprayed it with wd-40 which did no good. Then I wiped off the coil pack of all it's dirt and grime. The arcing stopped and it started right up!!!

 

[J_C]

Heh, I love cheap fixes.