95Cherokee

My 95 just failed emissions because of slightly high NOx.

What are some tips to bring it down? I'm going to use premium gas and let the cat warm up more when I go back.

I'm wondering if Seafoam will help any.

odgreen

When did you do a tune up last?

alpine.adrenaline

X2- even if it doesn't solve the problem, do a routine tune-up. Check plug gap, make sure your EGR is working, and check for any vacuum leaks (a lean mix is often a culprit of high nox). Seafoam is not a bad idea as carbon buildup can be another issue.

95Cherokee

I don't think my Jeep even has an EGR valve.

odgreen

It doesn't. Do a generic tune up.

alpine.adrenaline

Nope, you're right. Not sure why I was thinking Renix, but the EGR comes to mind because it draws most of those gases back into the intake. Have you seen your O2 sensor lately?

95Cherokee

Never changed the O2 sensor in the 7 years I've owned the Jeep but if it was bad wouldn't the CE light come on?

mschi772

They can be less than optimal, but not bad enough to trigger a CEL, so the answer: no, not necessarily.


The catalyst is the primary handler of NOx assuming your combustion temps aren't super high (if so, some Seafoam or even just drops of water down the intake while running to clean cylinder walls).

With MPFI, I doubt you're running so lean as to fail NOx, but if your injectors are starting to get cloggy, and/or your O2 sensor is getting a little senile....maybe. Check your fuel pressure. Check your injectors.

Premium gas will do nothing for you except waste your money.

Frankly, if your cat is old, it may simply be time for a new one. Performance-curve.com sells great ones that are very cheap.

95Cherokee

Combustion temps huh.

I was low on coolant when they did the test, the gauge was reading about 235 when they were done.

Added coolant when I got back home and it was back down to 200.