1997 chevy s-10blazer- i checked fuel pump good pressure, sparks from coil good, replaced crank sensor. it just cranks and cranks. once in a while it want to back fire after you let of the starter.

It probablly needs a distributor cap. I had one that was crossfiring in the distrubutor cap and kicking back hard against the starter.
It could also be that it needs new spark plugs. Pull one and check the gap. Spec is .060". If its severely worn to say .090" or more it may be causing your problem.

we check cap and spark plugs, check timing