Misfiring when wet

[AMC86MJ]

Here in NNY I have a stock 86 MJ 2.5 4sp. The problem it misfires when wet/damp in the mornings. The misfire goes away when it warms up. My fixes so far checked the pinch seam and resealed it (it was leaking), checked for leaking clutch fluid damage there is none. resealed all rubber plugs that go thru the firewall. Each fix I thoght would solve the problem but not yet so I am reaching out for suggestions any Ideas?

[Automan2164]

When was the last time you replaced the cap and rotor?

 

Rob

[AMC86MJ]

Never, it visual looks ok and is not cracked or carbon tracked. I have 132.000 on the original drivetrain.

[airspeed]

Take a spray bottle of water and spray around the plugs and plug wires while the engine is running. Chances are it is shorting out between the spark plug and rubber boot. Try the cap as well. Do this at night time and watch the sparks fly!

[88 Beast]

I had a similar problem om my 88, 4.0. After replacing cap,rotor,plugs and wires, still had problem. Turned out to be coil arcing out to outer metal ring when things got damp.

[Eagle]

It can also be the plug wires themselves. If the outer insulation jacket is wet/damp and the inner insulation is aged or deteriorated, the wires will cross-fire. Looks pretty spectacular if you pop the hood on it at night ...