My 1994 6.0 recently started running very rough and lost power. After having the car towed home I started doing some diagnosis and the culprit was a burned through distributor rotor. While I had it apart a friend of mine who is an electrical engineer had a look and made a suggestion.

The top portion of the distributor shaft has a bolt that holds the platform the rotor screws to. That bolt is a hex head and is also under the portion where the rotor arced and burned. His suggestion was to remove the bolt, as the sharp edges and corners of the bolt head encourages the electricity to jump to it. In its place, put a round headed screw, as that will reduce the tendency of the spark to want to go to the bolt over the rotor and then to the cap terminals. The screw is also slightly further away from the conductive strip in the rotor and that increases the air gap and the ability of the spark to jump through the rotor.

I did have some warning of the rotor failure, on a recent long trip the fuel economy was lower than it had been previously, and when passing the car didn't seem to have quite as much power as it previously did. It was subtle, but there of you were used to the car. So perhaps the moral is if the car seems to use more fuel than it should, an inspection of the ignition system should be added to the list of things to check.

Burned rotor:



The proximity of the bolt head to the burned portion is obvious:



The replacement screw in place of the bolt. The lock nut was on the original bolt and I reused it.

 

2 other things that can help are to cut off a portion of the upper part of the shaft that extends into the rotor, and fill the void in the rotor with RTV. It's not clear from your pictures if the bolt head or the shaft formed the path of the rotor grounding out.
I hope you also checked your plug gap and made sure they are .025". A larger gap there will also encourage the shorting out of the rotor. The rotor gap is in free air which becomes easier to jump than a spark plug under compression.

Jon

 

Yes, spark plug replacement is the next thing on the list to do. I pulled one and the gap was 0.030", so they will be regapped when new plugs are put in.

 

THX for this thread! I've noticed lack of power and poor MPG recently, but because I drive my conv less than 20mi a week lately I was thinking the ol boy was just getting tired (220K on him). I'll chk next time I go to take him out.