As title suggests, in wetter weather my 5.8 EFI runs rough after a rain or sometimes humid conditions. It does get better which tells me that the issue is moisture getting in somewhere.

I plan on installing a new Motorcraft coil within the next couple weeks and I installed a new solenoid about 6 months ago. On the solenoid, I think I put new ends on the wiring so they may be exposed to the elements.

Any ideas?

 

The high voltage ignition parts are the likely culprits, that includes the coil and all plug wires of course.

 

Cool, I had a feeling it might be the coil. The coil is yellow, so it's probably an Accel unit instead of factory. Something to be said for factory replacement stuff.

Also have new wires ready to install so sounds like one way or another I'll have it licked. Thanks.

 

Just chits & giggles try a can of dry gas, I did and to my surprise it worked.
Read an article saying that ethanol in gas attracts and or turns to water.

 

Sounds like moisture under the dist. cap, try spraying WD-40 under the cap and giving it a test drive.

 

That makes sense since the rough running is intermittent. I'll give it a shot.

 

Installed new coil and it did help smooth the idle out. Thanks

 

Went through and replaced cap and rotor as well as cleaing the inside of the distributor. Cap has a was corroded on #2 cylinder due to moisture getting into plug wire. Replaced plug wire and all spark plugs so it runs great, wet or dry.

For good measure, I installed a Mustang distributor boot to help prevent these issues in the future.

 

I know its fixed but here is a little trick we use at work is to take a spray bottle filled with water and spray the wires while it is running and see if it starts to run worse. finds plug wire issuse real quick.

 

Good to know. That's a great test to see if it's truly fixed as well. Thanks for the tip.