1998 5.7 Not Cranking Properly

[98GMC4x4]

1998 K1500 5.7 Auto. Sometimes if it cranks for longer than normal before it fires, it sounds like it hits a dead spot in the starter. it cranks fast and normal, then all of a sudden it will stop cranking for a second like theres a dead spot in the starter, or like 2 cylinders are firing at the same time. a little while ago I came home after a weekend of it sitting an it wouldnt start. it would crank and hit alot of these "dead spots", and it would fire occasionally, but not enough to start. took it to a shop, they unplugged the crank position sensor and cranked it till it was dead, then plugged it back in, charged it, then it was alright. then i went and had the timing reset, and it was about 98% good. is it possible the crank sensor is "half bad" and is making the computer compensate and advance the timing enough to make it fire on 2 opposite cylinders? whats my problem guys?

[Doug_Scott]

Quite possible there is a dead spot on the armature in the starter. When cranking over, it just passes over the dead spot. The commutator is about an inch across, so when spinning at about 100 times faster than the engine is, it is easy to pass over the bad spot. Sometimes you happen to stop right at the dead spot, so no start. You are not getting 2 cyl firing at the same time, not enough timing available to do that in an 8 cyl engine, maybe in a 16 cyl, but not an 8.

Have the battery tested, and if it tests ok, take the starter off and pull it apart. You may get away with just cleaning up the contacts inside the starter. I doubt you have the tools to test the armature, but if you have an auto-electric shop around, they will have the tools. You will likely end up replacing the starter, but at least you will get to see what it looks like inside.