Cant get my YJ to pass CA Smog

[jkruegel]

Im here in SOCAL and I bought a 92 YJ with the 4.0L injected motor with the 5 speed manual trans. I have now replaced the CAT, O2 sensor, fuel pressure reg, spark plugs, map sensor, coolant temp senor and thermostat. Ive checked the cylinder compression (150psi to 160psi). Ive used Seafoam in the engine and fuel. I can not get it to pass the 15mph or the 25mph NOx test. it will pass all the others. It has no EGR valve and I can not adjust the timing, Oh yeah, I opened the gap on the plugs to 0.045 instead of the 0.035 that is recommeded. Does anyone have any suggestions besides the C4 Im about to put under the engine.

 

[Zarski]

I wish I did. I have a 2.5 yj 93. That failed smog in NorCal. Same with NO. Text. But passed all other test. 2 years ago I put new cat in. Month ago. I put in new plugs, wires, cap and rotor. I need help also. Hopefully someone can help us.

 

[69jeepcj]

Have you replaced your pcv valve. Im not even sure if you have one but would think so. Not a expert, but the way I understand it is that the pcv pulls the unburnt gases from the combustion chamber and re-enters it into the carb to be burned completely. With out it the unburnt mixture go,s out your exhaust which I would think would raise your emissions. May be worth a try, their not expensive. hope it helps

 

[superj]

the bmw guys pour a few bottles of 90% rubbing alcohol in the tank and do a run before going to smog.

 

[72rtchallenger]

I found the advice below on other forums

I understand, the fact that the 4.0 does not have EGR puts it all on the cat. If you don't put a 3 way cat designed to reduce NOX emissions it's going to fail. at least this is one thing
I read about it
Also, a couple easy tricks... If you don't drive it much, especially before you test it, take it on the freeway and get the mph's up. And get a new tank of gas with the highest octane.
changing the oil helps
if running bigger size tires like 35 some have passed by putting on smaller 31

 

[desertrunner]

High nox is caused by high combustion chamber temp. The egr valve recirculates the exhaustinto the intake which in some way cools the temp inside the chamber eliminating nox. Unfortunately our nice friendly 4.0s don't have an egr system.

If all your other emissions pass really well especially co and ur nox is way up the problem is carbon buildup. Just went through the whole process myself with a 93 Cherokee. Replaced every last sensor I had and had improvment for my hc and co but my nox got worse. Then after much research I learned 4.0s from this time have nox problems usually from carbon buildup in the combustion chamber. So much carbon builds up that it actually increases the compression.

I had to pull the head off and clean a good 1/8 inch of carbon off the top of the cylander and another 1/8 inch of the black grime off the head. I was impressed by how much there actually was. Seafoam doesn't work. I tried it. Same with water and other cleaners. You have to physicaly remove it with a soft wirewheel being very carfull not to scratch any machined surface. After that and reseated the valves and my Cherokee passed no problem...

All said and done it set me back about 200 bucks to do myself.

I've read on another forum that a certified smog repair station will be able to do some kind of cleaning that will remove enough of the buildup to pass smog. Its something like 3 hours of labor.

Best of luck to you. Had a heck of a time with mine and I hope yours hoes easier

 

[69jeepcj]

Just a thought here, but they had emmisions testing here in our state years back and have done away with it (thank god). We had two testing stations close to home in two near by towns, I went to one and failed, the next day i thought let me try going to the other one just to see, it passed! the next year I did the same thing, failed at one and passed at another. Made no sence to me what so ever. Try going to another testing site if one is close by.

 

[jkruegel]

Thank you all for your replies. I have tried 2 differnt smog shops, same results.:???: I scoped the cylinders and the top of the pistons look real clean. I took the Jeep to a smog repair shop and they could not find any problems after going over it. He told me that the 92 4.0L Jeeps all had the same problems and that the Govt keeps lowering the emission levels making it tougher and tougher to get them to pass. He did say the engine is running lean and that causes high NOX as well. We are going to replace the computer and hopefully it has up to date software in it. If it doesnt then I will have spent enough to take it to the ref and challenge the test. If he passes it, then I have 2 yrs to figure out what and why.

 

[jkruegel]

Did you ever get your Jeep to pass? I still havent. I think the next step is to move it to Arizona. lol

 

[jkruegel]

The latest on my nightmare. I removed the head and found very little carbon on the piston tops and on the bottom of the head. I did find that the valves were out of round and severely pitted, the valve springs were a bit weak and the valve seals were worn and seeping. After a lot of cleaning and a valve job, I put it all back together. After putting a few miles on it I took it down for another test. At 15 and 25 mph test, it was staying green and then the NOx started climbing and it failed once again. After my blood pressure returned to normal I found that smog requirements vary from county to county. Here in San Diego, you have to put your vehicle on the dyno to test it. In other less populated counties they only do a RPM test at 1500 and 2500 RPM's. In short, it is good to know friends in other counties. :beer: My nightmare is over, for now.

 

[desertrunner]

That's how it is in LA as well. I too have some friends who helped me "pass" smog