Hi all,

Well... it failed. All the measurements are well under the maximum allowable (CO2, O2, HC & CO) except for NO.

The measurements have now qualified my car as a "gross polluter", and I'm probably on the radar of the CA smog ***** for the rest of my life!.

Anyway, some research is pointing to numerous prime suspects, What Causes High NO - Nitrous Oxide - SmogTips.com. Why did my car fail emission test high NO emissions. What is NO. My vehicle failed high nitrous oxide emissions test. Produced high NO. Common high NO failures. NO emissions. How can I lower NOx. Co

I wanted to ask the opinions of those who know much better than I do about the suspects on the linked page above:

1, Lean fuel mixture: Wouldn't there be accompanying symptoms like rough running or crappy performance? The car *seems* to be running fine.

2. EGR: Could this be just a case of cleaning the EGR valve? Or is it prone to failure and needing replaced?

3. Bad CAT: Shouldn't this throw up an OBD code? CEL is not on and there are no stored codes.

4. Carbon build up? Is this an easy fix? How....?

Any advice is greatly appreciated, I'm struggling to justify dumping more $$$ to have some grease-monkey guess at the problem.

 

The past 2 1/2 years I'ved owned my XJ6 I've had to get it smogged twice...
First time was because it was back tagged almost 2 years and I had to get it smogged for registration...
Took it to get smogged and first time it didn't pass because of high Nox levels. After failing it put me on the gross polluter list so next year I had to get it smogged again... this time it failed again. Tried cleaning EGR, replacing fuel cap, replacing exhaust manifolds, lucas deep clean which lowers nox levels

First year it failed smog, I had the rear catalytic converters replaced and drove it 1k miles after replacement and went through a tank of Lucas deep clean and it passed with flying colors..

Second year I had to get it smogged again did everything as I figured I just replaced the rear cats, and looking down into the first catalytic converters they still looked ok but took it to get smogged about 4-5 times and still wouldn't pass. I finally took it to a shop to get the front cats replaced and after removal of the originals it was clear that they were no longer good, the bottom of the "honey comb" had fallen apart but it wasn't obvious from above. But after replacement I took it to get smogged again and this time it pass without any issues...


If you know your cats have no been replaced at 118k miles... I would consider replacing the rear/under floor ones first if you have 4 cats..

 

John,
would the EGR valve not be a cheaper place to start? A new cat would help, as it would be more effective than your existing one, but as AlbBolivar's experience may suggest, it could be a temporary solution. Your existing cat should still be up to the job if the car has been well maintained.
You didn't mention whether you have any codes showing; some EGR faults would be reflected in codes. JTIS shows 5 separate codes for EGR related faults, and there are also codes for reduced catalyst efficiency (on the primary cats).

 

Thanks, I had already hoped that the EGR valve was the culprit but I just pulled it with the hope of finding it stuck and fixing it with an easy cleaning. Cheap options first, I'm well aware of that habit. I'm may have left 20 years ago but I'll never lose my Scottish frugality...

As for codes, there are none whatsoever. I would have thought there would have been codes if the problem was one of the prime suspects I've been told for high NOx:- EGR, Cats, O2 sensors.

Anyway, the Jag place I used to fix my nonswitchoffable CEL are going to give it a "smog-diagnostic" for $95, I'll have to report back with findings and see where we go from there. The smog station yesterday wanted $220 to bring in an outside mechanic for a similar diagnostic!

In true pessimistic style, I'm going to assume the worst then celebrate anything even a little less bad...

 

It took me awhile to actually believe that it was my cats there were bad and needing replacement... that is why I tried all the other possibilities. Even switched out o2 sensors.

I didn't have any CEL's or any warning signs except the high readings..