My 91. 5 truck with 180,000 miles was shut off in the yard last week and no start in the morning. I changed the shutoff solenoid fully expecting it to go. Well after too much cranking I held the throttle to the floor and it started. Fine for a few days, not many miles. Yesterday, I was driving on flat ground and coast to a stop, no warning, just quit. My son rescued with the other truck and for the heck of it I tried jump starting it. After about 20 mph it took off and I drove it home. Blue smoke and skipping a little. I backed into the garage and quit again. Oddly the grid heaters are not working now either, they were sporadic last week. The shutoff solenoid clicks when I take the wire on and off. Where do I start looking? Thanks