Smog and Nox

Does anyone know what would cause high nox? I heard timing, but it's not a real reliable source. Something about advancing or retarding the timing to lower nox. Could it be Cat or o2? I passed everything except nox. Any help is apprecaited, thanks

High combustion tempertures = High Nox. Yes Bad cat will cause High Nox as well as Bad O2.Advanced timing will also cause high Nox. try Switching Cat first and then see what happens.

so, in theory, using a lower octane gas and retarding the timing would help lower nox, correct?

Tools
Rachet with 12mm socket and 6'' extension (for adjusting timing)
Timing gun/light
5/8 spark plug socket and extension (locking type work best)
Parts
Air filter (if current one is dirty)
Spark Plugs (if current ones are fouled)
O2 sensor (if yours is potentially bad)
"Lean running ECU" such as a PM6 (say over the richer running PG7) if you have a DOHC ZC
Instructions How to pass emissions
Emissions is something that most of us will have to deal with at some point in time. Seeing as how many Honda owners swap their stock engines for ones from Japan trying to pass emissions with these "dirty" engines can take a bit more tuning. Also clean emissions does not really go hand in hand with performance either. Some sometimes this will require us to detune our engines (temporarily) in order to pass emissions.
Make sure the car is in good running order
The easiest way to clean up the emissions is to simply make sure everything is running right...
-Check spark plugs for fouling, if they are in bad shape replace them, you might want to replace them no matter what since they are a cheap item
-Check air filter. If you have a drop-in you might as well get a new one. If you have a K&N type you might want to "recharge" and clean it.
-Check O2 sensor. If you are running rich (you can usually tell by bad gas mileage and sluggishness) than you need to replace your O2 sensor. Bosch has ones you can get for about $40 (much cheaper than stock).
-Change the oil before you go to emissions, this helps some.
Tuning the engine to run clean
There are some things you need to adjust and check to make sure the engine is running as clean as possible.
-Use a "lean" ECU. If you have a DOHC ZC and usually use a PG7 (Integra ECU) you will want to swap it for a PM6 (Si ECU) since the PM6 has leaner fuel maps than the PG7. This is a good way to ensure you don't run too rich. I've heard CRX HF ecus can be used also and should run super lean.
-Check and adjust ignition timing to 16* BTDC (stock timing). On Honda crank pulleys 16 is the center mark (of the 3 marks). Running the ignition slightly advanced to 18*BTDC is good for performance but will raise combustion chamber temps which is bad for emission. Running the timing at 14*BTDC gives good low end torque but bad top end, so there isn't any real reason to go lower than 16*BTDC.
-Use the lowest octane gas available. High octane gas burning cleaner is a myth. The octane rating is the ability of the fuel to resist knocking. Basically the higher the octane rating the slower the fuel burns, and the lower the faster it burns. If you run high octane fuel with the ignition on 16*BTC or lower you are not giving the engine enough time to burn the fuel completely. This means you are spitting unburned fuel out of your tail pipe which is the worst thing you can do for emissions. Most stock Honda engines don't usually have high enough compression to require high octane fuel in the first place so you will get no benefit from it anyway. Even when running my DOHC ZC at 18*BTDC on 87 octane fuel I have no knocking issues.
What they test for
There are 4 basic emission they test for...HC, CO, NOx, and CO2. Depending on the year of your car you may not be tested for all of these, my 89 is not required to pass any NOx standards in the state of Maryland.
-Hydrocarbons (HC) - a form of emissions resulting from the release of unburned fuel into the atmosphere. They are produced by incomplete combustion or by fuel evaporation.
-Carbon monoxide (CO) - a toxic emission resulting from the release of partially burned fuel. A result of incomplete combustion of a petroleum based fuel. Cause by rich air/fuel mixture. As the mixture is leaned COs are reduced.
-Oxides of Nitrogen (NOx) - emissions produced by extremely high temperatures during combustion (remember before where I said advanced timing raises combustion chamber temps?).
-Carbon dioxide (CO2) - gas generated from the burning of a fuel that contains carbon. This is a result of any good running engine and the only thing you can do to lower it is buy a more fuel efficient car.
Examples
Here are my results from the last 3 times I went for an emissions test...
http://www.gutterslide.com/fourthgenhatch_mirror/photos/emissions/emissions-results.jpg
-D15B2 (DX engine) PASSED - I took this with basically everything on the engine being stock, ignition timing unknown and probably using 93 octane fuel, I did no tuning to this at all. I had a homemade intake on the car with probably a K&N filter, spark plugs probably 4 months old, and a stock O2 sensor. PM5 ECU of course, oil change status unknown. I'm not sure if I had a highflow cat on this at the time or not, I'm sort of leaning towards it still being the stock cat.
-DOHC ZC (1st try) FAILED - I took this with the ignition at 14*BTDC and using 94 octane fuel and fuel injector cleaner used a week before. I had a semi-dirty ebay air filter, fouled spark plugs, and a possibly rich running O2 sensor. I was using a PM6 ECU and did an oil change the day before. Highflow cat being used.
-DOHC ZC (2nd try) PASSED - I took this with the ignition at 16*BTDC and using 87 octane fuel and fuel injector cleaner used a week before. I had a nearly new K&N cone filter, month old plugs, and brand new bosch O2 sensor. I was once again using a PM6 ECU and did an oil change 3 days before. Highflow cat being used.
Notes
I'm not entirely sure if the standards my car has to pass in Maryland are the same as any other state. If your state has even stricter emissions you might need to go to even more extreme measures. I've heard you can add alternatives to the fuel tank such as toluene (basically F1 racing fuel) because it burns super clean. You can supposedly get the stuff at paint stores because it must have some kind of painting application (paint remover perhaps). But do some research before taking my word on that.

Thanks for the info, I'm in Ca which has stricter emissions, but I found that info very helpful, thanks again

so, in theory, using a lower octane gas and retarding the timing would help lower nox, correct?

Yes, it would help lower Nox
But don't go to far on the timing. Try to be only two degrees before the manufactor's spec. So if your timing is to be at 18 deg. +or- 2 deg set it to 16. Us smogger's have to check the timing as part of the smog. If your off by the two deg as specified on the emissions label, or 3 deg if not specified you would pass any farther and it's a fail.

To add to the above reasons for Nox: carbon build-up in the combustion chamber. This can increase compression thus increasing combustion temp's and Nox. Do a de-carbon treatment.

SH

Try some Sea Foam to clean top end b4 smog. Works Great :thumbsup: Where in Cali you at?

im from sacto baby! yeah go kings!

do you put the seafoam in your gas ?

Try some Sea Foam to clean top end b4 smog. Works Great :thumbsup: Where in Cali you at?

Is it just called Sea Foam or is there different types of the stuff? and I'm in San Diego, where u at?

do you put the seafoam in your gas ?

You can put it in your gas, but to clean out the c chamber pull off a vacuum line and suck it directly in the intake manifold with the motor running. Do about 8oz and let it sit for about 20 min. then run 8oz more thru. Repeat if you want to. I have used it a few times and it does reduce Nox.

I'm in Dublin/Tri-valley area East SF.
If that ? was for me..

SH