Failed Smog Check High Nox :(

[2.216VTurbo]

So Woody failed Cali Smog check today, HC's were super clean but the Nox was over allowable, I *think* it's cam timing as my adjustable gear has been auto-adjusting itself A couple weeks ago I noticed the slide in the adj cam gear was way to far twards retard so I loosened up the adjusting bolts and moved it twards advanced. Ran better and the random mystery detonation was cured but now I'm wondering if that's why my Nox was too high?? So I need to retest for smog check in the next few days, should I ADVANCE the cam or REDTARD it to bring down the Nox? The cat is good, it's a very low mileage OBD II that I just install for the awesome bi-annual testing here in the left coast state.

[mopar-tech]

Weak cat converter will cause high nox readings. Is it an aftermarket cat? Usually that is the problem right there.

[crusty shadow]

High NOx is caused by excessive combustion temps.
check the EGR- if its not working it can definitely cause high NOx ( if yours has an EGR system)
ignition timing too far advanced will definitely cause high NOx.
set the cam at neutral and reset ignition timing then retest.

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[contraption22]

So ridiculous that they still perform sniffer tests on cars that old.

[wheming]

CA needs that retesting money Mike. Plus, sales tax on parts and repair costs.
Seems like you think we live in a free country...

[going4speed]

why California worries about cars that old baffles me...what about all the 'smog' coming from mexico?

[2.216VTurbo]

High NOx is caused by excessive combustion temps.
check the EGR- if its not working it can definitely cause high NOx ( if yours has an EGR system)
ignition timing too far advanced will definitely cause high NOx.
set the cam at neutral and reset ignition timing then retest.

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The cat is very, very fresh. It's an OBD II (look at those HC numbers, Woody has 20% injectors...) cat that only gets bolted into various TM's for just a few miles every other year


Hmm, ignition timing eh? I'll admit, since woody is my only automatic equipped TM I don't really know how to check the ignition timing I've been setting it by the little cant the distributor should have to it. I've only used the flywheel marks/window method(yes CTS unplugged) on my manual trans TM's, so whats the trick with flexplate equipped cars?

Yes, Cali and their fees, now they have my $43. TWICE

[shadow88]

The autos have the same timing mark, but it;s built onto the torque convertor (unless some aftermarket makes don't put it on.) Maybe even set it a little on the low side like 10 or 8 degrees to help cool the combustion temps with that fancy new catalyst to help it out?

[Rrider]

Local smog place has a bunch of my money too. No clue on the cam, but ignition they only allow 3 degrees retard from std. I have the same failures due to nox on my vans even with new cats, everything else is a pass. I thought about water injection to lower combustion temps. It is legal in CA.. haven't gotten around to seeing if it actually helps yet. I did go for the lowest cost CA legal cat, when there were more expensive options. That might be part of it too. I also have 3" from the cats back which maybe leans/heats things up versus the restrictive stock muffler.

What kind of exhaust do you have? Were you running the stock tune for the smog?

[RattFink]

Dang, cars over 25 years old here in Atlanta area don't require emissions. High combustion temps, egr, etc. can all cause high Nox, but a good "CAT" can cover up a lot of NOX too.

[johnl]

The companies that sell the test machines are in the crony corruption loop with the politicians and their pet regulators too

The poor bastards who buy/set up a smog test shop are forced to buy a new machine just about the time that the last machine has paid for itself. It's a cozy relationship between the regulator, the AQMD, that writes the regs that force the test shops to buy new machines and the companies that sell the machines.

Then they take back the old machine on "trade in" and re-sell it in another state where the regs are behind those set in California. Of course the terms of the trade-in in the new sale rip off the smog test business owner coming and going. And, conveniently, only "certified"resellers can re-sell the old machines. That, of course, locks out the existing owner from reselling the machine himself and preserves the monopoly aspect for the insider cronies and their regulator pals

[looneytuner]

We got the tests back to independent shops. The guy that pushed the bill through got punished by the powers that be.

[OmniLuvr]

so nox is caused by high combustion temps, so basically 3 problems (and maybe a 4th or 5th or 6th) to much ignition advance, not properly working egr, or engine running LEAN, its very hard to tell by the sideways photograph that is showing the whole paper, I really need a clear view of just the numbers. but it looks like CO is very low (indicating lean condition) hc should be low (that is unburnt fuel from misfires) high nox (indicator of lean) and marginally high O2 reading (hard to tell exactly) but you should read almost zero unless you have air injection.

other things that cause high nox could be higher compression, calibration, tire size or gear ratio (incorrect rpm test range) old fuel, cam timing, and burning oil (from rings or pcv system) the last 3 are usually followed with higher hc though

what motor and calibration is in woody, and is it supposed to be equipped with egr? what "+20" inj are you running? what grade fuel?

[black86glhs]

Retard your timing and run it back through. Unless you have a wide band and can see what the mixture is doing all the time, you really need an exhaust tester to see what the issue is.

[mopar-tech]

The cat is very, very fresh.

But is it aftermarket? The over the counter cats don't have enough platinum in them to do the job right.

HC/CO numbers mean nothing. My Daytona would sail through emissions testing with single digits with NO CAT at all with +40's

When they started testing NOX the jig was up, no cat would show up right away with high NOX numbers. I kept a factory cat with slip connectors about for the annual testing. The same cat went on Jon's Spirit when it failed NOX with an aftermarket cat, it sailed right through with an OEM Mopar one.

[Rrider]

If you retard your cam timing enough, the exhaust valve would be open after the piston reaches the top of the stroke.. get some exhaust gasses back in there kinda like an egr. I would think for nox that is what you want.

[2.216VTurbo]

OK, I like these suggestions. I will retard the cam and the ignition timing (it's an aftermarket high stall V6 torque convertor with no marks on it) and try it again. I didn't think about the tire size thing Scotty, they are way huge for highway 'gear' effect(215-70-15) Would putting some 195-50-15's help you think?? I can easily change those out if it makes an appreciable difference?

Every TM I have uses this cat, I've not failed due to NOX on any of those other cars. Yes it is an after market cat Gary, a high end $300.one not a cheapy. I may be wrong but my understanding has always been that the OBD II cats had TWICE AS MUCH catylizing metals in them?

Motor is a built top end 2.5, ported everything, +1 valves etc etc that's on a slightly tired all stock bottom end with 130K Crosshatch looked great and no scoring when the head was off 5-6K ago but ring tension is likely pretty low.

It's a boostbutton cal and to me that stuff is witchcraft, I don't get involved in burning cals, not my thing.

I do have an innovate WB 02 but unfortunately the bung is in the 'test pipe' where the cat is living temporarily. It's certainly doesn't smell lean at idle, generally I think it runs rich as the cal is a very close cousin of Rob's race cal that runs his Daytona.

[A.J.]

These cars are very easy to get through emissions, even when modded. I second Gary on the cat. Vic had a turbo car that failed NOX and he insisted the cat was new/good because it was barely used but sat on his shelf for a few years. He brought me the car, I put it on the lift and put my heat gun on it and it wasn't heating up. He put another one on and it passed.

[cordes]

For what little I can contribute, I'll offer that the Chrysler guys cheated the emissions a bit by lowering the timing in vac at part throttle. This is one of the first things I take out when doing a cal. It gets a couple more mpgs in my experience. If you've been guesstimating the ign timing, and had the timing bumped back up in a cal I would think that could leave little if any room for error for anything else.

[OmniLuvr]

so the number 1 biggest problem is the 2.5, they were equipped from the factory with egr for a reason, they have issues passing nox. so if the egr is not hooked up or not working properly that's a problem.

tire and gear size will make a big difference, I didn't have much time to squint at your sheet to check rpm during lunch break, but its not as "low' as I expected. the lower the rpm the test is at for the givin mph the more it has to "lug" and that will cause a higher knock situation. but your rpm at 1850 and 2050 isn't what I would call "low" rpm, but could still have an effect, so smaller tires isn't a horrible idea. ive had to test vehicles in a lower gear (keep it in first instead of shifting to second) to get vehicles to pass, but the new "star" natzi smog stations now take that into effect and red flag techs for doing that now.

the other problem is robs cal, boost button cals are awesome for performance, drive ability, and fuel mileage... but that means they are not always great for emissions. I have passed with a simple cal swap no problem, but it needs to be stock (the mp cal still passes but bairly). is this a swapped in 2.5 using lm electronics or can you switch the cal back to stock?

also, fresh tank of 91 is very important, no alcohol cheating, because that will make you run leaner. the biggest problem I am seeing the is in the smog sheet numbers, look at what you tested for both hc and co, and the higher 02 reading (which is usually 0.02 or 0.01) and look at what the "average" is. you might even be able to make it slightly richer by increasing the fuel pressure, but that will only last as long as it takes for the computer to compensate.

but, you really need to figure out actual ignition timing, that will be huge, I wouldn't mess with cam timing to much, unless all the other things I have listed have been taken care of. id say cat, but since the other numbers are so low, to me, it says that its "working" but the engine is running just lean enough at those rpms that its not cooling the combustion chamber as much as needed, and theres not enough extra fuel going into the cat to get it "warm" enough to make the chemical reaction happen.

lastly, if egr is hooked up, and when "tested" the vehicle rpm drops, there could also be a problem with free'r flowing exhaust, that it doesn't have enough back pressure to let the transducer valve send vacuum to the egr valve, making it not effective...

good luck