91 MJ failed emissions

Hydrocarbons- 5.71 <-----Failed
Allowed- 2.4

NOx- 8.94 <-----Failed
Allowed- 3.75

CO- 33.1
Allowed- 80

1991 MJ 4.0, 185k, I think it has the stock cat so I was going to start there. Recent tune up and seems to run good, keeps steady at 210 degrees. Any other ideas?
Nathan

O2 sensor.

Rev

Ditto O2.

Just had my '88 XJ smogged and failed with a HC reading 4x's the limit. Turns out the connector to my O2 sensor came apart. Put in a new one anyway. Passed on the retest.

However, clearing up the HC will likely make the NO rise. This would be the Cat. The guy at the smog station said that if you run rich like that for a long time, it can trash the CAT. Mine made it by a very small margin.

Yeah it was very poorly taken care of by my brother in law for a few years. Ran real bad when he gave it to me so replacing the cat is probably a good idea anyway. I will give the o2 sensor a shot too. Anyone know of a good place to pick one up cheap?
Nathan

They're $20 at Autozone for the generic one (no connector) and $55 for the "OEM" ones (has the connector).

You'll get what you pay for - replace the HEGO with either Bosch or ACDelco, and you'll be fine. Also, I'd not bother with a "universal" sensor - they rarely are (there may be conflicting reports from the field on this, but that's MY story and I'm stickin' to it...)

15 years is long enough for a cat - I've rarely run across "lifetime" parts from the factory. I've replaced the ones I've done with PFP units that were actually meant for BB Chevvy applications - just cut the flange off of the OEM unit and have a pipe stub welded to it at your local muffler shop (probably cost you five bucks, unless you have a welder of your own.) Especially if you have a manual, that bolted join is just too handy to lose...

I haven't had any trouble with the Smog Nazis out here due to the catalytic converters I've used, and I can probably dig up smog numbers going back years to validate this...

5-90

Autozone lists the Bosch "OEM" for $59 so I will pick that up. I will also just grab the bolt on Magna Flow Cat from Summit for $75. Hope that works.

Make sure that you have the correct amount of timing in the engine. Too much timing will make your Nox reading high. A simple thing like an oil change will also help lower your HC. O2 sensor will more than likely get you under on HC & Co. The Nox may take a little work. Also don't be afraid to drive your jeep hard on the way to get tested. You would be amazed at what this can do. If you still fail let us know as I am a certified emissions inspector in the state of PA.

Oil change right before the test knocks numbers way down. Get a can of BG's 44K into the tank and the injectors will get a major clean up too! My '93 XJ with 240,000 miles passed WA state emissions with a gutted cat after running a can of that through.