Thank you, Doug. That's useful information. I did the test suggested by George and it seems to be isolated to the #5 cylinder. There was no change in the idle when I pulled that wire and the spark plug is black and kind of wet looking. All the other plugs are dry and tan. I had to stop for the day but I was going to check and see if that plug is making a spark at all. Or maybe the better idea is pull the valve cover and see if either one of the #5 valves are stuck? This happened so suddenly that I have to believe the cause was also sudden, like a sticking valve and not the gradual wear of the valve guides. I'd appreciate hearing how you guys with a lot of time and experience with these trucks would go from here.
