tylersXJ

got a 94 Cherokee sport all stock put new 02 sensor on but emissions are still high, mechanic said had high nox.. Not sure what this means? any advice helps.. Thanks guys

1976Mustang

This might help

https://www.cherokeeforum.com/f2/fai...152144/index2/

DFlintstone

Nitrogen Oxide "forms" at combustion temps that are high. 2,800, 3,000 * maybe. One purpose of the EGR valve,(Exhaust Gas Resurilation), is to reduce combustion temps and the formulation of N0x. Likely a good place to look. Right off hand, that is all I have..now.

The valve is low on the exhaust manifold, (middle) controlled with vacuum, controlled with a solenoid. I think. 94 is similar to mine I believe. My EGR solenoid is on my drivers inner fender, should apply vacuum to it when the puter' says. That opens it to let exhaust into the intake manifold. I can't say for sure mine's working or not.

tylersXJ

No Egr on the 94 modols, ran seafoam during test and tested cat and it was good

1976Mustang

NEVER run ANY additive during an emissions test, that usually screws up the results big time. Do the test about a week after you get the additive out.

DFlintstone

Whoops! No EGR?

Radi

Nope. They just overlap the intake and exhaust valve timing a bit instead.


How far off were the test results? Pretty close or way off?

tylersXJ

Not too off but not too close either

Radi

Typically bad O2 sensor, bad cat, heavy carbon deposits or something leaning the mixture out causes high NOx. Any sign of leaks in the intake or pre-cat part of the exhaust? Are you still running the original cat? How was it tested?

DFlintstone

Well howdy Radi. Well that's bitter-sweet news. Guess some of us need to pay attention to witch cam then.

Yes, Tiler, Radi IS the man.....but I just don't recall seeing allot of high Nox,

DFlintstone

A load of deposits raises the compression ratio? Gotta go, just a thought,,,,

Radi

Yep! Which increases the temperature. Carbon deposits can hold heat too.

tylersXJ

Cat tested good and just put new o2 right before

DFlintstone

Just fielding a question. Is it different getting an estament to pass smog, than say to have the belt changed? If you are not somehow "stuck".... I mean, we all have seen what they do. Sometimes another shop can help.

High Nox (too high compression) on a 94? Do you hear pinging?

mudpen

High Nox means it's running lean, had the same problem last sept. I also changed the o2 sensor that made it go up, check your CCV it's easy to replace and cheap. Look at your exhaust manifold it most likely has a crack where the pipes connect, that sloved my high readings. You could also go with a cooler plug I belive the plug is champion RC9YC with the same gap that should help but it won't fix the problem. If you can pull a plug and post a picture also the reading you got from the smog test would help.