I have a 92 Bronco. It has a 351W in it. I bought a crate engine and installed it. I have got it running but around 2,000 RMP it starts to run really rough and the tak will jump all over. I have replaced most everything that I can think of. with each new part it gets better but not good. It runs the best when I have driven 5 or so miles and then turn it off let it sit for more than ten minutes and start again. Took it to a mechanic and after six weeks he still hadn't done anything to it yet. Have done all work by myself.
New parts
Crate engine from oil pan to heads
distributor
tfi
fuel pressure regulator
fuel injectors
original fuel rail dented so got one from junk yard
fuel pump
fuel filter
throttle positioning sensor
o2 sensor
spark plugs/ wires/ cap/ rotor
pvc valve
egr valve
map sensor
idle air control
ignition coil
Had headers on replaced with manifolds with the idea of headers leaning out the engine

OLD Parts
upper and lower intakes
throttle body
ecu
wiring harness

If any one can help would really appreciate it.

 

May be an obvious question, but have you checked the timing?

 

The timing is set. We had the timing light on it and when we revved the engine the timing is retarding. When the timing retards, that is when it starts acting up. The distributor should advance the timing shouldn't it? What would cause that?

 

check out broncozone.com they'll have some ideas