2000 4.3 Backfires on start up

Ok, I have a 2000 4.3 Blazer, First the fuel pump went bad replaced with new one, then a little while later I had to replace my fuel spider with the MFI upgrade. Only problem I have left now is once in awhile on start up it will backfire cause the engine to engage with the starter causing a grinding sound. I thought for shure that the leaky fuel regulator was causing this but it's still there. I had one mech tell me that he has seen bad crank shaft sensor cause this and take out starters. Any ideas would be greatly appreciated. Dist cap, wires, plugs, have been replaced.:banghead:

Moisture inside the distributor cap causes that problem on my stuff.