Trouble starting 4.0 motor swap

I swapped short blocks from a 91 4.0 to a 87. Sensors are all straigntened out, Transmission is bolted up and distributor is timed properly, with spark. If I spray some starter fluid in the intake and turn the motor over the, it back fires through the intake and ocationally through the exhaust, but never starts. Any suggestions?

Also my throttle body spring seems to be gone, if you open and let off it does not want to go back to the original position.

Okay, you said sensors are straightened out but, just to confirm -- you are using the correct CPS for the year of the chassis and ECU, right?

If so, backfiring thriough the TB sounds like a timing issue. First, confirm that the spark plug wires are in the correct order (1-5-3-6-2-4). Then confirm that you set the distributior so the rotor points at number 1 when the number 1 piston is at top dead center on the compression stroke. Remember the distributor goes around once for every two revolutions of the engine. It's a common error to pull number 1 up to the top and set the distributor, but forgetting that number 1 was on the exhaust stroke rather than the compression stroke.

She runs!, I was on the exhaust stroke