Topic: Passing CA smog... Almost there. High NOX at 25?

[TahoeYJ]

Trying to get the old girl to pass smog, it's passing with flying colors except at 25MPH nox.
It's legit almost perfect on HC and CO numbers, 15mph nox is 78. Allowed like 700.
Failing 25mph allowed 600 something, fails with 960.

Brand new cat, O2 sensor, ran seafoam through and did full tune up, took my intake off and put the factory on with a paper filter to choke it up and try to richen it up. All vacuum lines good, injectors and fuel pressure checked and pressure is fine. Checked thermostat, it's working fine.

I don't see what would cause such a significant jump in NO at 25 vs 15 and cause it to fail??? Unless it's just a fluke machine at this particular shop I keep going to (I would go elsewhere but screw paying $80 for another shop when I can get a retest for $30). I'm at a loss, I don't know what else to check. It just seems mind boggling that it would pass NO numbers at 15 so insanely low, and jump up stupid high at 25mph.

[Jeffy]

Did you change the oil before testing?  What's the running temp of the engine?  Is the fan working?  An engine that overheats will produce more NOX.  You don't really want to choke the engine.  That can cause it to run lean which can cause high NOX as well.  The difference betwen 15 and 25 is the engine works harder.  Is the cat a CA Legal one?  Though I don't think that matters as much since I've passed with both.  All numbers should be really low and should be easily passed with a properly running engine.

[xpage]

ever figure this  out? I have the exact same issue.

pass at 15 easily, fail at 25. About the same #s

15 - 50 ppm  nox  - pass easily
25 - 1200 ppm  nox fail

[Jeffy]

ever figure this  out? I have the exact same issue.

pass at 15 easily, fail at 25. About the same #s

15 - 50 ppm  nox  - pass easily
25 - 1200 ppm  nox fail

I'd lean towards the cat.  How old is the cat?  Either isn't getting old and not working as efficient or it's not hot enough.  I know if I don't run the engine for a while before taking it in, it gets close to not passing on the 25 mph test.

[95 Lowbuck]

Had the same problem with my '95, the smog shop said it was running lean.
At first it didn't make sense, but I guess the Cat will not get hot enough if lean.
I wound up running a bunch of injector cleaner in the tank, and got a new Cat.
180k on the Cat btw.

[dwtaylorpdx]

Luckily OR has smog test stations and the one I go to is < 1/4 mile off the highway, make sure its up to full temp and it passes.
 
If I had it to do all over,, It would have a megasquirt inside a factory ECU box, Swap the original back in to test as needed.

The V8 transplant is getting closer ,, I figure at 12 MPG may as well get 350 HP.. LOL

[Jeffy]

Luckily OR has smog test stations and the one I go to is < 1/4 mile off the highway, make sure its up to full temp and it passes.
 
If I had it to do all over,, It would have a megasquirt inside a factory ECU box, Swap the original back in to test as needed.

The V8 transplant is getting closer ,, I figure at 12 MPG may as well get 350 HP.. LOL

For CA, I don't even think they would check.  I've thought about going with a Holley Sniper EFI.  Way overkill but it would work with any engine.  The only "problem" would be to wire up a circuit that lights up the CEL and Brake lights when the ignition is turned on.  That would be easy to do though.  Otherwise have two seperate systems and put them on a 2-way or 3-way (for a kill switch) switch.

[dwtaylorpdx]

Yea,,, OR doesn't do age roll-off any more,, my 94 will always get the probe...
And no more engine swaps on cars that are OBDII or newer.. Unless its a engine from the same manufacturer..  Cause somehow a Hemi is not as dirty as a 5.3 Chevy?? arg.

Luckily a 94 YJ is pre-obd2 and I can still do the swap to a V8.
While I can still drive it.. LOL

I think my investment in my 2.5 would have worked out way better with a standalone, the Jeep ECu is basically a digital analog hybrid that you cant do much to.. (I've fiddled with it a lot never got it to really make the power it should.)

[Jeffy]

Yea,,, OR doesn't do age roll-off any more,, my 94 will always get the probe...
And no more engine swaps on cars that are OBDII or newer.. Unless its a engine from the same manufacturer..  Cause somehow a Hemi is not as dirty as a 5.3 Chevy?? arg.

Luckily a 94 YJ is pre-obd2 and I can still do the swap to a V8.
While I can still drive it.. LOL

I think my investment in my 2.5 would have worked out way better with a standalone, the Jeep ECu is basically a digital analog hybrid that you cant do much to.. (I've fiddled with it a lot never got it to really make the power it should.)

Arnold repeeled the 30 year rolling exemption for CA before he left office.  Kinda screwed us over with that compromise.  That was when he was trying to look green and selling his Hummer's.  When he left office, I think he bought a Unimog.  Still, we have 1975 and older are SMOG exempt.  Would love to have the Jeep exempt as it's 27 years old.  But if I don't do an engine swap, I'm probably going to go a supercharger.  With 4.56's it should be a good compromise.  The supercharger isn't CARB legal but it's bolt-on so it's bolt-off as well.