Hello people,

It's that time of year for me again, and emissions isn't goin my way. I've already failed twice, but on both occassions I'va had EXTREMELY hi NOx. From what i read, this is caused by the combustion chamber temperature being too high. does anyone know of the best wayt o dramatically reduce these temps?

As for my car, I'm riding in a 92 civic SI hatch.

 

How is your timing? How do your spark plugs look? Is your car stock?

 

yeah we need to know more about your car.

 

And if we could get a copy of the results.... would help too. Just not the Nox numbers all the numbers.

To start...

Check timing
De-carbonize

If all the numbers are up-> CAT and O2 sensor.

 

Right now the only performance mods that i've done to the car are the following:

stainless steel headers
short ram air intake

As for maintenance, i've already had to put on a new cat, and intermediate pipe. The funny thing is, after i put on the new cat the NOx went up, but everything else went down.

As for the timing, the guy who replaced the water pump and timing belt made sure that it was spot on, but the spark plugs themselves look a bit white.

As for the copy of the sheet, i will have to get back to you guys on that one. Unfortunately i don't have it on me at the moment, but from what i've already been told from other mechanics, the O2 sensor should be fine since all the CO and HC emissions are WELL below the limit.

 

I have the same issue with my civic vx..
My last smog check I failed Nox.
HC 9PPM passed
CO 0.9% passed
NOx 1600 failed

Thinking my EGR passageway is clogged I got a new (used) intake. I verified it wasn't clogged by pouring water in the egr passageway and watching the water come out.

I'm going to smog it again in a few days with the new intake. I also thought about running without a thermostat to lower combustion temperatures, but not sure how it will affect smog of the other gasses.

Let me know what you do...
Gary

 

Follow me here for a minute...

So for a healthy cat the A/F ratios need to flip-flop on either side.(needs to go rich to lean to rich)and so on.

Your O2 sensor is your main sensor that effects your a/f ratios. The O2 sensor is suppose to do this flip-flop 8-10 times a second as designed for the health of the cat and to provide enough O2 to store in the cat to reduce emissions.

The 02 sensor is the only sensor that does this flip-flop. If the cat is not getting this flip-flop it is not storing enough 02 to do what it is designed to.

HC and CO are easier to reduce than Nox. Also the part of the cat that reduces HC and CO are in the front of the cat and the Nox part is in the rear so the front part is getting just enough to reduce the HC and CO but there is not enough 02 left to get to the Nox part. So it then is less efficient.

In short O2 sensor is what I would replace.

 

Whooho, I passed smog today!!

Prev tests:

MPH HC CO NO
15 9 .02 1826
25 8 .02 1635

Today's test

MPH HC CO NO
15 38 .09 185
25 19 .05 178

I cut my NO by 10 folds!!!

So, how did I do it?
Of order of importance, I think:

1. timing from 16 to 13 deg
2. clean EGR passageway by replacing intake with a known good one (I would put that as #1 but my intake was not completely clogged when I tested it)
3. cleaned carbon from intake ports on the engine and new intake (esp near the injectors)
4. new plugs - one step colder gapped at .041-.043; original one was probably 5 years old and had a gap of .60-.70 when taken out
5. New air filter (probably did nothing - I should have kept the old one in since old dirty filter will increase HC (which is what I want).
6. Cleaned EAVC (screen plugged) - not sure if this can affect NO

I went in early before temps hit 100 deg. Last time I warmed up the car for 30 minutes driving it on the highway. Not this time. I drove it to the test only station 5 mins away turned it off and waited. Engine cold when the guy arrived. This should be #3.5 .

My goal was to richen up the mixture somehow. I think retarding the timing helped, but not sure how it affects gas mileage. Since it's a commuter, I will probably advance it back to stock or higher.

Anyways, this smog saga has come to a close for me. I spend so much time on it that I was getting frustrated and was wondering if it was worth it. Since I commute about 120 miles/day, I can say it was worth it.

Gary


Modified by garyhgaryh at 5:44 PM 9/3/2007


Modified by garyhgaryh at 11:56 PM 9/4/2007