I am in need of some assistance here. I have a 1990 F-250 4x4 with the EFI 4.9L. I recently bought it, and replaced the fuel filter, O2 sensor. Ran it about two weeks, started having problems with cold starting (It's 0 pretty regularly here) so I pulled the codes, and replaced the IAT and ECT temp sensors, as indicated by the codes. Also replaced the MAP sensor, and did a complete tune-up (plugs, wires, cap, rotor, coil). Now, the truck has no power!!! I can get it to accelerate, but it just hits a wall at around 1800 rpm, and just is gutless above that. It will rev just fine at idle, and in the low gears (manual tranny) the problem is so bad, but trying to get it above 45 mph is almost impossible, it just bucks and hesitates, also under some light throttle conditions. I tested the fuel pressure at the rail and it is within specs on both tanks/fuel pumps and the regulator checks out. The only code I now have is 41, which correlates to "O2 sensor indicates lean" I am leaning towards replacing the fuel injectors, but am also concerned that I could be chasing a bad engine management computer or ignition module. Anyone have any experience with this sort of problem??

 

I do not know a lot about the 4.9 But put a vac gauge on it and see what the vacumn does when it hits the wall. I thinking slagged cat or muffler maybe.
Hope this helps
Gasman
Do you have Gas?
Propane Execeptional Energy