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CorruptCulture · 02-19-2013, 11:15 AM

Hello everyone,

I have a 1998 Jeep Wrangler that failed emissions at 15mph. It was very close to passing, failed by only 10% over the limit (600PPM vs 550PPM) on NOx. All other measurements were very good.

I'm really at a loss for what I can do to get it to pass. My smog guy is pretty cool, let me run the test with my hood up and a big box fan in front of the air intake. The cat was wrapped in foil, I seafoam'd the engine the day before and ran a tank of CRC Guaranteed to Pass the few days prior.

From what I've read, elevated NOx is caused by lean conditions and a hot engine. I can't retard the timing, and there's not EGR on the 2.5L engine. O2 sensors are only 15k miles old. I've tried chasing down a vacuum leak but I can't seem to find one.

Someone mentioned running "cooler" spark plugs. Is this a thing?

Two years ago I managed to pass by taking off my 31" tires and running 28" trailer tires, I don't have access to those anymore.

Any help, ideas or feedback would be appreciated.

02-19-2013, 11:15 AM	#1
CorruptCulture A Motorgen O.G. Join Date: Jan 2007 Posts: 402 Tweet	Smog Help - High NOx Hello everyone, I have a 1998 Jeep Wrangler that failed emissions at 15mph. It was very close to passing, failed by only 10% over the limit (600PPM vs 550PPM) on NOx. All other measurements were very good. I'm really at a loss for what I can do to get it to pass. My smog guy is pretty cool, let me run the test with my hood up and a big box fan in front of the air intake. The cat was wrapped in foil, I seafoam'd the engine the day before and ran a tank of CRC Guaranteed to Pass the few days prior. From what I've read, elevated NOx is caused by lean conditions and a hot engine. I can't retard the timing, and there's not EGR on the 2.5L engine. O2 sensors are only 15k miles old. I've tried chasing down a vacuum leak but I can't seem to find one. Someone mentioned running "cooler" spark plugs. Is this a thing? Two years ago I managed to pass by taking off my 31" tires and running 28" trailer tires, I don't have access to those anymore. Any help, ideas or feedback would be appreciated. __________________ I'll fix your computer.