I have a 1990 base Jeep Cherokee 4.0 L, with 241,000 km. Never had a problem with it and have done most service myself. Recently it has developed an annoying problem that has gradually worsened with time.

At cruise speed anywhere between 80 km/hr and 130 km/hr there is a steady miss that feels as if several cylinders are misfiring or not firing at all. Under acceleration OR deceleration, the miss goes away entirely. Return to cruise and the problem returns. It seems that any time the engine is under load or is unloading (decel) the problem goes away.

I have changed plugs, rotor, cap, tps, HT leads, all sequentially, nothing solves the problem. I don't know where I can get a code reader so I have never looked at codes. I have never changed the O2 sensor or the injectors.

I just completed a 1,600 km trip and it stammered most of the way.

Help

 

On OBD-I vehicles you don't need a code reader, you just have to do the paperclip trick to get the CEL to flash te codes.

 

If you got the time I would pull the fuel pump and check the rubber line that goes to the fuel pump. I had a similar problem. the line was rotted and also it was barely connected.

 

the cel trick is a little harder on the AM jeeps... chrysler is the simplest (key on, off, on, off, on and count blinks) where the older ones usually had the odd connector under the hood. could be crank pos sensor, my buddies was an 89 ad did the same thing, but it also became harder to start when warm

 

Vacuum leak somewhere maybe?