CA smog failed, high CO

I just took my 90 cherokee to get its smog done and it failed the functional gas cap so i bought a new cap, but it also failed the 2500 RPM CO test. My CO was 2.08 when a passing max is 1.0. I understand when you don't pass the CO at high RPM its because the mixture is too rich. I checked my air filter and it was almost completely soaked in oil and garbage flushed up from the valve cover. even the hose that vents the valve cover into the airbox was mostly plugged with black stuff.
I bought a new air filter and replaced the valve cover vent hose. I bought some acetone to put in the tank, and tried to check the oxygen sensor but couldn't figure out how to do it as the haynes manual didn't make sence. I did change the oxygen sensor last time I didn't pass smog so I don't think its bad.
Do you think changing the air filter and the hose will be enough to lower my CO levels as it will be able to breath better at speed, or what else should I do?:tear:
FYI: Idle levels (co2=13.2, o2=1.7, HC=23, CO=0.0)
2500 RMP levels (co2=13.3, o2=0.0, HC=56, CO=2.08)

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check plugs, distributer cap, rotor, and basic tune up stuff, also check for exhaust leaks and other stuff along that nature first. but I am pretty sure high co is from being to rich so I would check plugs and ignition first then move on. and about the o2 sensor its a toss up i bought mine two years ago and tested last month and it was bad so i failed. changed o2 and cat ran seafoam through the tank and passed no problem... i would say don't rule the 02 out because it still is a possibility.

Apart from the tuneup stuff recommended above, high CO is usually the sign of a failed cat. There's no mixture adjustment on 4.0-litre XJs per se, so assuming the oxygen sensors are still good I'd blame the cat.

If you've got a ton of oil buildup on the air filter, it's probably time to clean out the PCV system as well as flush the crankcase and valve cover; all that crap would be making its way down the exhaust to the cat and depending on how unburnt it is by the time it reaches it may have contributed to burning it out.

Seafoam is your friend. Be sure to hit the EGR valve and throttle body as well while you're at it, but it definitely sounds like at least a new air filter and cat are in your future. And whatever you do, DO NOT go to the test with ANY additives in your fuel.

I'd like to check the o2 sensor to see if its good or not, but my manual says to either measure the resistance between the "white wires" and it should be between 5 and 7 ohms. My o2 sensor only has a red, black and grey wire, so there are no white wires to measure between. (between the red and black wires measure 7.3 ohms and I get nothing with any other combination) The other way is says to check it is to have the vehicle at operating temp and unplug the o2 sensor then measure the voltage on the o2 sensor side of the unplugged connector against ground, and it should read between .1 and 1 volts. But how does it show voltage if it has no power going to it? Does the o2 sensor just generate power by itself?:confused1
I believe the guy I purchased the jeep from (my dad) 4 years ago replaced the cataletic converter just before he sold me the jeep, do you think its gone bad already?

Have you gotten it tested again since replacing the air filter? A clogged air filter alone will cause it to run rich, I would imagine, due to the engine getting less air than it expects.

If you've been running rich for a while, then your cat may be bad already, as running rich really fouls up everything in the exhaust system. Is your tailpipe really sooty? With the engine completely warm and running, can you smell unburnt gasoline in the exhaust? Those would be indicators of a severely rich running condition, in which case you have a lot of things to check, and I would start by making sure the engine is actually getting to the correct operating temperature.

If you don't have these symptoms, then I would fix the blow-by problem and make sure nothing else is restricting the air intake, maybe change the plugs if they've been in there a while, and get it tested again. If it fails a second time, then I would start looking at the cat, O2, tune-up, etc.

Hope this helps- Rob

No I haven't re-smogged the jeep since I changed the air filter (I just finished changeing it now). I did check the plugs and they were in good shape, although they did have a very small ammount of carbon im sure due to the clogged air filter. I really don't want to check it again and not have it pass because I believe you only get one free return visit without having to pay for another smog check.
Whats the best way to check the o2 sensor?

I tried checking the o2 sensor again and while it was running the grey wire was giveing some very wierd readings to the multimeter. It kept jumping all over from 0 to 10 to blank to negative 9, back to 9.5 positive back to blank, etc. I assumed that was bad and pulled it out and tired measuring it after heating it up on my propane kitchen stovetop and it did absolutely nothing. So I replaced the o2 sensor and tried to get it in for a smog today and they told me to come back on tuesday like they didn't accept walk-ins except they let someone walk-in before and after my appointment on thursday morning.:gag:
I did check the tail pipe and it didn't smell like fuel, just exhaust, and my finger was covered in carbon when I touched the inside wall of the exhaust pipe.
Does anyone have any other suggestions?:scared:

That carbon(tailpipe) was prob. from when it was running rich before you changed the air filter and hose.
It wouldn't hurt to throw in a new O2 sensor and cats. are fairly cheap. I' d have it "re-smogged" first.
Moving out of the Peoples Republic of Kalifornia might be your last resort.

How many miles on your 90 XJ? Mine failed emissions, in CO, when in need of a rebuild on the engine, for the same reasons. Also, I would check the CAT(catalytic converter) if your XJ is high miles; mine failed after 280,000 miles, but I have heard when they are close to failing, or need replacement due to damage or structural weakness, they sometimes cause the vehicle to fail emissions, too.

BD
Somewhere in the Rocky Mountains

My '88 failed the last time by a wide margin. Put in fresh plugs, cap, rotor and filter. When I pulled the air filter, I saw a huge puddle of oil in the bottom of the air box. Throughly clean it, the CCV orifice and all other lines. Then found the connector to my O2 sensor came apart. Since it was probbaly to original, I changed it.

Easlily passed on the retest.

Can you fail an inspection for having a cracked exhaust manifold?

it certainly doesnt help at all but it would depend on how big the crack is. mine has a very little crack and made no difference. but, a big crack or little hole would prob fail just the visual inspection if they look (most of the time in cali they look) the running test would prob depend on the size of the "problem"

Just to update anyone in the future with the same problem, I checked my O2 sensor and it was bad, so I replaced it. I replaced my Air filter, unplugged a clogged PCV tube to the airbox, and checked my spark plugs but they were good. I just passed the smog this time around, so my couple fixes did the job.:cheers: