95 Cherokee high NOX

My 95 Cherokee failed the Ohio emissions test due to high NOX reading.
HC, CO, and CO2 all all well within limits. Combustion temp is supposidly high. I have looked for the EGR valve as shown in my Haynes manual but find nothing which looks like the pictures shown. Does this inline 6 with fuel injection have an EGR valve? If so, where is it located? Think I'm on the right track with this diagnosis? It has 211,000 miles but runs great, uses no oil between changes and seems fine otherwise.

I don't have a jeep, but with my car, when it had a high nox reading for emissions testing, it was due to a washed catalytic convertor. I changed the cat and it passed fine.

its behind the airbox. its kinda spaceship looking

The last time it was tested, 2 years ago, there was the same problem. A state recommended emissions repair shop put on a new convertor and it passed just fine. It has been driven about 25,000 since then. It seems that a convertor would last longer than that unless something else was wrong. I have heard that a new convertor will get you passed on high NOX, but I would like to fix the root cause. High combustion temp leads to high NOX. Improper timing and EGR problems can cause high combustion temps. The book says timing on the 95 is non-adjustable. I had the air box off last month when I put on a water pump and don't recall seeing anything that lookes like the EGR valve but I will take another look tomorrow. Any other thoughts?

Lean mixture is all I can think of; how is your air filter? On older cars with carbs, a clogged air filter would cause a rich condition; however on fuel injected engines the reverse can be true. You might want to check/replace the air filter, and check the intake for any buildup.

How about some fuel injector cleaner? If the injectors aren't bringing enough fuel to the cylinders, it could cause a lean condition (assuming the computer can only adjust so far)

Filter is changed regularly and is about 3 months old. I usually run injector cleaner through it every other oil change. Performance wise it runs great and milage is a consistant 23 per gal. Last time this happened, I did all new plugs, wires, distributor cap, filters, the best cleaner, check computer codes (there were none), compression good on all cylinders, no vacuum hoses leaking. When I went back for the emissions test it did worse on the NOX. I took it to a state recommended shop where they slapped on a convertor and ran it back through the test station. It passed easily. I guess that I can put another convertor on to get it passed but I would like to figure out the real cause.

I certainly understand you wanting to get to the root cause, but it might just be the high mileage. From what I've read while looking up NOX emissions, it seems it's from a lean mixture and high temperature in the combustion chamber. If you're not getting any ping or detonation, you might want to leave it be as your engine sounds like a good one.

I've heard of people putting 90% rubbing alcohol in their tanks to reduce emissions. It's worth a try at a couple dollars - much cheaper than a new converter every time the state inspection comes up.

Just reread the original post, and I apologize for not answering your initial question about the location /existence of the EGR valve. I don't know the answer to that, other than maybe go pick the brain of a friendly Jeep mechanic.

Thanks for the input. It looks like another convertor in my future. I'll get it passed and be good to go for another 2 years. As you say, it could be the high mileage. They didn't start testing for NOX untill 2 years ago so I can't compare the tests before that to see if it was a gradual prosess of higher and higher NOX readings as the engine aged or if it happened fairly quickly. Would be good to know.

You're welcome. And after thinking about it for awhile, my wife's 99 had high NOX also - but low enough to pass in Maryland. Maybe it's just the nature of the beast.

Since they just started 2 years ago, you may want to look into a waiver, if one is offered.

Have a good one, glad to help out.

I saw online somewhere, about building an adj. map sensor, possibly that would be your solution that would lean or richen the motor, posibly that could be going bad?

Good point, might be worth throwing a part at the problem

I'll have a look for that website...

Put a new convertor on today and passed with flying colors. I'm good to go for two more years. Thanks to all who offered suggestions.

Hi all! FYI the adjustable MAP sensor is at www.go.jeep-xj.info. Glad you're fixed up!

show-off, I couldn't find the link again...