Been having same prob with my 97 3.9. Ive changed complete tune uo twice iac ,dist, intake gaskets. computer, temp sensor. I was wondering if anybody has removed the heat shields around the spark plugs. and if it helped less chance of arcing there

 

This is a really dumb question.. if it sounds and you think its arching on something.. have you tried running it at night and then watching for the arch? I did that on wifes car and found a broken plug wire arching against the motor..

Just curious..

 

Exactly how i found some arcing. Just thinking it may be arcing low in the heat shield tubes and possibly not able to see it happening