High nox and hc California smog...

Need help diagnosing my problem
Sniffed it today and had high nox and hc,
Hc measured at 15 mph were 166 max was 124 average says 45
25 mph measured at 121 max was 104 average says 36
Co% passed but measured at 15mph was .34 max was .75 average .14
Measured at 25mph .27 max was .95 average is .16
Nox measure at 15mph was 787 max was 714 average is 393
At 25mph it measured at 606 max was 616 average was at 308
The smog tech said I needed a new cat, which I may but the reading are so close to passing I was wondering is there anything else I should look at before replacing the cat, I appreciate all feedback

Google "naxja.org California smog high NOx" for the thread that covers this for starters. Lots of prior case histories and what worked in one thread.

Sounds like you need a new CAT.

Is it stock, if not what mods does it have, tire size, gearing etc, miles and year?

HC is usually unburned fuel, high NOx can also be too lean i.e. high combustion temp. Run a bunch of injector cleaner through it or guaranteed to pass stuff. Tune up and make sure compression checks good. Adjust timing if possible. Drive it hard, real hard, to get the cat heated up if it's still got its core.

Year & engine, please ?

Things to check. I go through this system every two years, my 4.0 comes out clean with very low numbers

Vacuum lines: Are there any leaks or missing vacuum lines. Does your heater/air blow out the front vents or just defrost?

Any smog equipment removed. Is it nicely warmed up (do you take it in immediately after a nice 1/2 hour drive, orright out of your driveway to the smog shop)?

Have an EGR? Is it working, all vac lines to and from it?

Vacuum test to see if cat is blocked/clear.

AND...

If you have never replaced the 02 sensor, do it.

Once you get past all of this and think CA is too restrictive, remember, we have no vehicle inspection. Like (e.g) we don't have to make sure all the tiny little things like back up lights and horn and e-brake are all working.

Dont get the NTK sensor like I did.The one on the left.
It lasted a month before it quit. Smaller and no ceramic insulator for some reason. Bosch is the best.

my2monkeys said:

Dont get the NTK sensor like I did.The one on the left.
It lasted a month before it quit. Smaller and no ceramic insulator for some reason. Bosch is the best.

Click to expand...

Have me worried about my Denso's now!

Second request, what forking year jeep is it? If it is Renix, yes you should only use Bosch. They designed the OEM Renix sensor. It is special. The later year HO 4.0s like NTK O2 sensors from all the posts here.

my2monkeys said:

Dont get the NTK sensor like I did.The one on the left.
It lasted a month before it quit. Smaller and no ceramic insulator for some reason. Bosch is the best.

Click to expand...

88 4.0 aw4

I failed CA smog last year. Here's the combination that worked for me:
1. New EGR. Mine was dead.
2. New EGR solenoid. Mine was dead.
3. New o2 sensor. Mine was dead.
4. 180 deg tstat.
5. Colder spark plugs. Champions, I don't recall the part #.

Didn't need a new cat. Do a search for the o2 sensor and egr tests.

Forgot to mention that I had high nox too.