My '90 F150 4x4 is running very rough, jerking as i drive. Can hear somewhat of a ticking noise almost like a lifter. Every now and then it will snap out of it and drive normal. When having problem, poor acceleration and very little horsepower for a 351. Replaced plugs, wires, and fuel filter. Performs like this weather I use front tank, or rear tank so I dont think it is a fuel pump. Please advise, cannot seem to figure this out.

 

I would start with checking out the EGR valve and sensor and all pipeing for the emmisions. If there is a hole in any of the emmisions pipeing it can sound like a lifter ticking or a bearing going out. If there is a problem eith the EGR valve it can cause the syptoms that you are describing. After that then start looking into the air pump.
You might want to get the codes read if you don't have a code reader.

Good luck

 

I dont' know if this would be it, but could it just be a bad/noisy injector? My injectors would make a ticking noise sometimes, but they were still good. Or was it worse than what an injector would do?