'95 YJ not passing smog, high NOx...help!
my '95 yj (2.5L, no mods) is not passing smog. specifically, the NOx emissions are way too high, and the CO emissions are right on the border of passing. i've been doing a lot of reading and research into fixes, and after the 2nd check today i'm still failing. wondering if you guys could help.
here's what i've done so far:
1. tune up (distributor cap and rotor, spark plugs, wires, oil change)
2. seafoam treatment (through vacuum line off brake booster, half a bottle)
3. found two exhaust leaks before catalytic converter, had them welded
4. new fuel filter (to make sure adequate fuel was flowing)
5. put a couple gallons of 91 octane in before test, drove around to make sure system was at full running temperature
at this point, i'm basically wondering what else i can do...i know some guys have changed their catalytic converter and that seems to help, but so far as i know a cat doesn't affect NOx emissions at all, so why would that help? o should mention that PO (my buddy) replaced catalytic converter back like 5-7 years ago, so it's not the stock unit. also, haven't checked o2 sensor but in theory wouldn't the jeep throw a CEL and a code if the o2 sensor was too rich or lean? or maybe i can't rely on the system to verify o2 sensor operation?
i will say that when i had the exhaust shop look for and fix exhaust leaks, they said my manifold was supposedly cracked (though i don't see a crack anywhere). also, the forward most and rear most studs for the exhaust manifold are missing...that being said, she passed smog with flying colors two years ago when i bought her and those studs were missing then too.
basically i've spent a couple hundred damn dollars on this so far with some very big ticket items on the horizon...besides taking it to a shop to have them diagnose it, is there anything else i can do?
btw, i am aware that this model of jeep does NOT have egr, so that's not something i can look into.
thanks for any suggestions you can provide, this is driving me crazy and i just don't trust that a cat is going to fix my problems unless someone can describe why NOx would be reduced with a new cat.