My '94 Facelift 6L has barely passed the last few years, but failed this year.
It had not been driven much in the months prior to testing.
It starts, idles and runs great. (98k miles) Plugs and oil are just a 2k old.

Tested both L and R sides, a week apart, as they are basically separate.
CO% was good <.2%, but HC and NOx were high.
HC 116 (Limit 78 ppm), NOx 810 (Limit 767 ppm).

Have since checked for any cracked or leaking hoses or connections.
Tested coolant temp sensor, and running temp.
Also tested the O2 LAMDA sensors and they seem to toggle 0V-.9V as expected so engine seems to be running closed loop and in control.
Also rearranged the plug wiring to help minimize any misfire, per the TSB.

It is suggested that replacing the CAT's would improve it but that is not a cheap undertaking, and if there is something wrong, possibly a poor course.

How to diagnose if the CATS are indeed working?

If I drove it more regularly, would it clear out any old HC in the oil? Does the oil even have any great effect?
My plan is to run another 3-400 miles of frequent driving this week and then get a pretest to see if it does improve after some frequent use.

 

When ever my smog tests were due, I'd drive the car a few days before with higher revs, kind of a sportier method to blow the cats free and clean up their surfaces. A really bad nasty fail was a glorious pass after a 2h drive with revs exceeding 5000 rpm in normal traffic. Cost some fuel but worked. This though was on my XJ8...

If you barely drive the car and it never really has the chance to declog the cats, it is worth a try.

 

Ugh, SMOG fail. Been there, but not for a decade or so. Failed cats in each case!!!


The things do have a finite life. Recovery is iffy. The real fix is replacement!!


1. My 94 Jeep failed a few years ago. Not long after I bought it, used. Suspicious as it "passed" just before??? Just barely though!!! New converter, and all was/is well.


Two years later, up again. Oh, s..., the older couple ahead of me were advised their 94 Jeep failed...... but, yahoo, mine passed.


2. I've developed some pre test things to do. At least one is sound, the others may or may not be.


A. Let the fuel tank level drop to less than 1/4. Add about 5 gallons of Chevron Supreme. $'s. But high Techron content. Add a truck size can of Techron. Resut, a super dose of injection cleaner.
B. Swap or clean the air filter element.
C. Change the oil and filter.
D. Drive energeticly for a day or two pre test day.
E. On test day, just before going in, take a freeway run in 3rd. Objective, get the cat/s good and hot for the test.


Yes, there is a test for cat function. If any doubt, money probably wasted. Two holes drilled in the pipe. Sniffed pre cat. Sniffed after cat. Any better? Hoes plugged, bucks collected...


HAPPY NEW YEAR TO ALL


Carl
Carl