I have a 199 Pontiac Bonniville with 3800 series II engine.I had crankshaft sensor replaced as well as the serpentine belt. Now it turns over but won,t start. It;s getting fuel.Has new ignition module, all three coils packs are new, as well as MAF MAP,battery,plugs and wires. what could be cause of this?

Loose fitting parts. yea, like hoses, grommets, aftermarket pcv in a loose or missing grommet, split hoses, hoses that fit like socks on a rooster. Especially hard starting when cold. when it's warm out it might start, but hard starting the first time, right? Any codes in it ? can you hear "tick tick tick" etc. when cranking? They eat aftermarket modules for 3 meals a day. They also can have a timing chain issue and concerns that lead to checking the cam sensor. So correct the simple stuff, and then restore your GM parts where you can. Even used GM parts can be better than some aftermarket stuff I have seen. But take the list from the top, getter done and try starting as you go. get a good battery charger on there, and remember if you have a security system, enhanced codes can be read with the newer scan tools to help diag any issues there.

How much for the engine

I have to say the vehicle may have been looked at with diagnostic test equipment after the answer sent them to a technician or to get scan and pinpoint tests. It was very likely their security system is their problem cancelling spark, or they are not using the highest quality parts even though they are new parts. Extended crank occurs, and the battery suffers deep cycling. The tests steps are bypassed without a diagnostic plan. Even with the parts done the false air leaks can keep it from starting. 4 months ago they made no reply after asking. Busy seeking good diagnostics, I trust.