This truck was running but sometimes would make a 'popping sound' - especially under a load. I am posting for someone so know little info - as it was relayed to me. One recent morning, the truck would not start. It sounded like really low cranking compression. The back and forth movement of crank pulley indicated excess 'free-play' so next thing done was to expose the timing set to have a closer look. This confirmed chain had jumped two teeth on cam sprocket. New parts were installed, correctly I was told, and then cover, damper and pulley re-installed. With nothing else disturbed (during repair) engine was turned over but did not sound right. It would 'labor' for a second or two and then turn normally but no indication of 'firing'. These Vortec engines are apparently timed by a cam sensor in conjunction with the computer so nothing would result from rotating distributor back and forth, however, the rotor is pointing at No.1 terminal at correct time. Is there something that was over-looked? Could the computer timing be set as for the position of the camshaft before the repair? There is a fuse that states 'Crank' but no power to it. Does this mean anything? This is about all I know from the owner and I did see and hear engine cranking. Any ideas?