Acceleration Problem

I have a 92 XJ Limited, 4.0L, AW4 Trans. Recently I have been having a problem when trying to accelerate. From a stop, there is not much trouble as long as acceleration is slow and gradual. If I am getting on the highway, as soon as the trans down shifts, the engine starts to sputter and backfire through the throttle body. If I floor it, it downshifts to 2nd gear and takes off.

I have replaced the fuel filter, cleaned the K&N air filter, replaced plugs, wires, cap & rotor to no effect. When I pull the ECM codes, all I get is 55 which I believe is the check code for "beginning of codes" or "end of codes".

Can this be caused by a plugged catalytic converter? Or is my XJ just possessed?

OK ... I have 213,000 miles on this thing. I'm getting tiered of waiting for it to heal it's self

The problem might be your Throttle position sensor (TPS). I just had mine replaced because of similar problems. I would also have to start out slow, and at higher speeds it would kinda sputter. The part should only be around 50$

Check your fuel pressure... I had the same problem when my fuel pump was giving out... Good luck

I was thinking it might be the TPS. A GM mechanic friend of mine says it might be the catalytic converter (CC). I have a new CC on order. Maybe I'll try the TPS as well.