Rebuilt motor starts, but backfires.95 Jimmy

A few days ago, we had the problem of no power after the starter. MT was kind enough to help and we were able to rectify the problem. Now that it starts,it backfires.
DOes anyone know if on the manifold, are there supposed to be 4 bolts or 5. It says 4, but there was an extra spot where one was placed.:confused:

Which manifold are you referring to?

A manifold leak usually won't cause a backfire, check your timing and ignition system. particulary your firing order and crossed or dmaged spark plug wires.

Does it backfire through the intake or out of the exhaust? On acceleration, deceleration or idling? Totally different sets of diagnostics and possibilities.

could this be the spider injector or egr acting up

could this be the spider injector or egr acting up

It depends when and where it backfires. A lean fuel mixture can cause induction, (backfire through the intake).