I am having what has been narrowed down to a CPU issue. I have a 1994 ZJ with the 4.0, Automatic, 4x4 w/no security. Am I stuck only looking for a 94 with those same options? I have a second ZJ but it's a 1993 4.0, auto, AWD, w/security. Not sure if I can swap those 2 CPU units to verify it is the issue or will I have to find a 94 with all the same options (or lack of options lol).

The issue I am having is while trying to smog the jeep the Nox will be nice and low then out of nowhere it will shoot up from 85 ppm to 1300+ ppm. All the other numbers look great and are way lower than the average. I checked the fuel pressure under a load. I have changed the cat, O2 sensor, computer temp sensor, TPS, Intake manifold temp sensor, Maf, and all the numbers have stayed the same. I also put my stock injectors back in (has the neon ones), went 1 temp range cooler on the spark plugs, and put in a 180 thermostat in. This lowered the NOx to 0 then as we were running it on the dyno the numbers shot way up then came back down then shot up again. All the wires have been checked, no intake, vacuum or exhaust leaks either. After talking to a few older smog techs they have said they have seen this before and they swapped a cpu from a different jeep or just replaced the cpu and that took care of the issue.

Anyways any help is appreciated,
Max

 

Oh and I also ran seafoam through the intake and fuels system. Also did a compression test, all between 120-125.

Max

 

A 95 ZJ PCM should work for you. You may want to try and change your coolant ratio to 70% water and 30% antifreeze. More water to the mix will absorb the heat faster and more efficiently, that may be enough to lower the combustion chamber temps to lower the NOX emissions.

 

I am right about at that ratio on the coolant. I forgot to add that.

Max