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 was gonna say, didn't you have this exact problem last time? Anyway, yes you can run cooler plugs but I wonder if that's going to get your combustion temps down enough to lower NOX. When you Seafoam'd did you let it sit for a good long while, like over night? Finally, could be injectors if they're not spraying enough fuel. Are they stock? If so, how many miles?

Yeah, exact same problem as last time.

When I seafoam'd I let it sit for about 30 minutes, the directions say 5 minutes.

The injectors are the same ones that have been in there since I bought the car 4 years and 40k miles ago. I'd rather avoid replacing these. The smog check is for a buyer. He's fully aware of the condition of the Jeep and the smog issue, but regardless, it's my responsibility to get it smogged before the sale.

Smaller tires would probably fix the problem.

EDIT - Let's say I ponied up the ~$250 for new injectors, is it something I could do in an afternoon? I have all the standard mechanic tools, just no specialty stuff.

I know it isn't that hard on the jeep 4.0L and the 2.5 isn't that much different.

You can go to a junk yard and grab a pair of smaller tires (only put them on the rear)

Haven't changed them on a Jeep, but if they're anything like other vehicles I've seen, as long as they're reachable, not hard at all. It's possible there is just a tiny air leak around the injector seal causing it to go lean. But, unless they're in a crazy location to get to, the job is more like 30 minutes total, not hours.

BTW, you can talk to John Supino (a.k.a., jsup) of Injectors Plus (sponsor ad see left) about rebuilding yours. It's going to be way less than $250.

Good to know. I just did a few youtube and google searches, it looks like it should be fairly simple.

I think I'm going to try to pull them, soak them, and then replace them with new o-rings. That should cost about $10 for new rings and hopefully it should run a little smoother.

What gear did the smog guy run the 15 mph test in? The last time that the Cobra just passed the guy ran both 15 and 25 in second. When my brother ran the car at his old shop the day before he ran the 15 mph test in first and the 25 in second and it passed easily. Granted the only reason it just barely passed was because of a burnt plug wire but running the 15 mph test in first helped.

You bring up an excellent point. He ran the 15 in second and the 25 in third. Both of those tests are ran at about 1700-1800 RPM because of that. I should ask him to run it in first and second respectively. Those little 2.5L loves to rev.

Maybe it's worth having him do it again like that before taking a look at the injectors? I know the guy is getting tired of seeing me though and I don't want to push my luck.

Is there a limit to how many times one can take the test?

EDIT: No limit to how many times you can take the test....
And auto trans must be run in "D"

Under the rules of the smog check...all manual trans cars are supposed to be run in 2nd gear. They ding us each time we run a car outside the desired rpm. If we have too many deviations they will lower our technician rating. In the past they knew we could fudge the numbers, but they had no way to enforce it. With the changes this year , I got let go from the smog shop I was working at. My " Follow up pass rate " was too low. That means if I pass a car, and it fails it's next test (2 years later ) I get dinged because the state believes I did not check it close enough. The state knows some cars will fail after 2 years, but smogging millions of cars, they know what those percentages should be. If my averages are outside the limit, I get a " Fail" rating as a tech, and do not qualify for the program.
I try not to answer smog questions on open forums anymore either. I commented on a smog thread on the Camaro site and got PM'd by a BAR rep.

Here is a recent rpm deviation I got dinged for...

Inspector Test Deviations Incident:


Inspector
GALANTE, PAUL (EA141356)

Incorrect Gear Selection
Station Number-230396- Inspector Number-141356-


Test Date-11/24/2012 1:37:24 PM - MY-1993 Make TOYOT-

Model CAMRY-
' RPM5015 RPM2525 Certificate
1 2227 2202 XN854922C

They're just not going to be happy until we're all wearing grey unitards and riding electric mopeds.