My 84 d150 has an intermittent miss in one cylinder. Engine is the 225 slant 6. Everything has been replaced new from the plugs to the rotor . Five of the plugs are burning and look fine and one comes out wet with some carbon deposit build up. Tried new plug and wire but still the same. On start up seems to idle smooth for about 2 minutes the starts missing. Any thoughts on this problem would be appreciated.

 

have you checked the compression on that cylinder? have you also checked the reluctor in the distributor? maybe it is damaged causing the coil not to fire on the one cylinder. may also be worth swapping plugs with one of the other cylinders and see if the issue follows the plug. it is possible for a brand new plug to be bad. also what ignition system does the truck have?

 

Try a new cap and rotor with either brass or copper electrodes. The standard aluminum contacts sometimes develop faults quick. Also, when you pull the cap that's on there, look for any fine lines that might be thermal cracks.