Put in a bottle of Redline SI-1 a day ago, gonna run it through and then try to test again. The air filter is new, first thing I did with it as the old one was crazy dirty.

 

Apologies, sometimes on the forum, we can go off onto a tangent. Let us know how you make out after the next test.

 

And it better be good news, or the conversation may be triggered again.

 

XJPoirer
I bought a '96 XJ last spring from the original owner and the CEL was throwing the bad Cat code. They had all of their repair records and they had replaced the Cat three times prior to me buying it. I assume that the mechanics were throwing parts at it and never did resolve the root of the problem. I live in CO as well and somehow passed the emissions test last spring after resetting the CEL. This probably isn't much help but maybe there is something to these Cats in the 96 Cherokees. Let us know how the test goes. I have a 97 TJ as well and I can't tell you how nervous I get every time I have to go in and get these damn emissions inspections for these ancient vehicles. I am looking forward to moving out of the state for retirement......

Regarding the emissions testing, I would say that most cars 10 years or newer probably don't even need an emissions check since the pollution controls have become so efficient nowadays. But, like most government programs, once you start one, it's almost impossible to kill it.

 

Appreciate all the replies everyone. I have a question in regards to the Redline Si-1 additive I put in. Would I be better waiting till I run the tank low so I can fill it with pure gas or should I be fine going to test it with that in the fuel?

 

Probably fine to leave it in the tank. Whatever you add to clean the fuel system and valves/combustion chamber, I'd also strongly recommend giving the engine an Italian tune-up before you go in for the inspection. This will clean things out and likely cause you to run cleaner. If nothing else, it sure is fun!

 

The last emissions test I brought my 95 XJ to in CT was performed with a gutted CAT. Ran the tank to below 1/4 then added 3 bottles of isopropyl. The engine has about 280k on it. Was it the alcohol? Was it the carbon clean up? Who knows.

 

Several pieces of good advice from others in this thread. Hope she passes with the new cat installed!

High NOx occurs when combustion gases exceed ~2500 degrees. Usually this means a lean condition caused either by air that enters the engine unmeasured (and therefore unaccounted for by the engine computer), or by less fuel being injected than the ECU "thinks" it is calling for. Any vacuum leaks downstream of the mass airflow meter will lean out the engine. The mass air meter itself may be dirty or defective (usually easy and worthwhile to clean this anyway). If fuel pressure is below design spec the pulse width being specified by the ECU will not be sufficient fuel; dirty injectors can do the same.

Excessive carbon build-up in the combustion chambers effectively raises the compression ratio, also creating higher combustion temps. Sometimes in older vehicles you'll find a combination of these factors "stacking" to create excessive NOx.

The oxygen sensors will, to a point, cue the ECU to correct for the lean condition but typically that only leads to a "trim value" or variance of about plus or minus 10% or so in most factory systems. So if the dirty airflow meter, vacuum leak, weak injector flow, etc. lean condition exceeds this variance the engine will still run lean and create excessive NOx. These are the areas where I'd look first.

As others have suggested, a reasonably priced code scanner will be worth its weight in gold.

 

Finally passed!

 

Nice. I'm going to guess the Cat did moat of the job with such a drastic reduction on your results.

 

Good deal!

 

For sure

Cats are a wear item that needs renewal in every vehicle once they have been depleted

Palladium is the other metal apart from Platinum.

I cant understand peoples reluctance to replace them when they have reached end-of-life

That is the only job of the rear O2 sensor, to alert one to Cat failure..they do no absolutely nothing else