1989 Chevrolet Blazer Replaced valve cover

I replaced the valve cover and pulled and cleaned the rocker arm shafts put it all back together and I t won't start all the pulleys move and it will back fire out the tbi after a few try can't figure it out?
all the spark plug wires where taken off and put back checked the plugs seem fine.
The engine makes no noise when trying except for the pulleys winding.