OK guys I need some help. I have a 99 S10 Blazer. It will run fine for months on end and then will just not start. It turns over fine but wont start for anything. The problem is NOT temperature or humidity related. My neighbor is an ase mechanic and has been trouble shooting for months with no luck. Here's what we've tried so far:

The truck is not throwing any codes.
Its not the fuel pump or filter or relay or a fuel line.
Its not the plugs or wires.
The engine is getting fuel.
We've replaced the plugs & plug wires, The distributor, the alternator, the ICM, relays, fuel pump & filter. We checked the voltage at the injector pack and its good and the injectors are firing. We've checked and or replaced most of the fuel and electrical system and still no solution.

The engine appears to be getting furl and spark but won't start. Seems impossible but thats what we've got. So what are we missing?

 

the crank sensor is a common problem with these trucks and pretty easy to change