Hello all,
Recently I had my 99 4.6 f150 engine lock up... We replaced it with a 2001 4.6 with 2500 miles on it, a great deal really.. All went well and bolted up fine and the truck fired right up, but now I have a miss and am getting codes PO420 (Catalyst efficiency below threshold bank 1) and PO171 (system to lean). After doing some research, after the fact mind you, I found that the 4.6 engine got the PI heads in 2001, not in 99 like the 5.4 as I had thought.. Could the increased compression be causing any of this condition?
I am grabbing at straws so any help would be appreciated.. Thanks in advance

 

did you swap PCM's? if not i would try having the keep alive memory cleared so it would relearn fresh what it takes to idle.

also double check all vacuum lines and air intake tube connections and make sure mass air flow sensor is plugged in.
also check to make sure all coils are tight and check to see if you have any injectors leaking out on top of the manifold. this happens when you swap the injectors and rail sometimes.

the cat code could be a bad cat monitor O2 sensor. or wires pulled out or unplugged. could be bad cats but i would check out the sensor first.

 

Something tells me that the old PCM is still being used. What is casuing the miss? Fix that first. One of the casues of P0420 is a cylinder misfire. Also,P0171 can be caused by a bad injector. One other thing to check is an exhaust leak near the O2 sensors.

Regards

Jean Marc Chartier

 

Did you use your old intake manifold on the new engine? If you did then you have an intake leak. The two manifolds are not interchangeable. They will bolt up, but the intake ports will not line up correctly.