jlsmi2

I have a 92 Cx w/ 94 b18c1. I've passed at NJ MVC facilities three times with this current set up. The car has a carsound high flow converter.

I failed NOx, but passed HC and CO%. Numbers were as follows:

NOx standard: 1372 // my car: 2379!
HC standard: 173 // my car: 147
CO standard: .97 // my car: .64

Magnaflow/CarSound's website suggested these possible causes: EGR, lean AFR, leaks, run-in converter, use larger converter.

I found this suggestion in an archived article:

This is a suggested order for NOx failure of things to check:
1. EGR System
2. O2 Sensor
3. Timing/Spark Advance
4. Catalytic Converter
5. Incorrect/faulty thermostat
6. Coolant Temp Sensor may be open
7. MAP Sensor
8. MAF Sensor
9. Other sensors/switchs (uhhh yeah, ok)
10. Fuel Injection System
11. Faulty On-Board COmputer
12. Computer PROM
13. Internal Engine Repair


Does this list offer good advice? I think first thing I'm going to do is check to make sure there are no exhaust leaks. I failed once a few years ago and the problem ended up being a bad gasket.

Also, something I noticed when looking at my older inspection reports is that it appears that my HC and CO% numbers have increased each time I've had the car inspected. Could this be an indicator of a bad o2 sensor? Converter deterioration?

What are your suggestions? Thanks

thesmogman

It looks like all of the numbers are up. Which points to the cat. Is there a O2 reading on the test? If it is over 0.2% during the tests would also point to the cat.
Unless you have an exhaust leak then that can throw off all readings. A leak before the cat would do this also.

As for the O2 sensor, It is responsible to cycle up and down so the cat will get the proper amount of O2 to work correctly. So what I am saying is it might be the O2 sensor.

You could try a de-carbonization treatment. I have seen it drop 300ppms but not 1200ppm's.
Double check your timing. Set it to spec or one degree before it
Good plugs with proper gap.
Clean the air filter.

If you want to hear what I would do... Cat and O2 sensor. Unless there is a exhaust leak. Then I would fix that.

jlsmi2

yea. driving around today listened to it and think there might be a leak before the cat. i'll get under it and find out.

jlsmi2

what about egr?

thesmogman

Well you got the motor in front of you, Do you have an EGR valve?

If you do it can effect the CO and of course Nox. But would not mess with HC unless it is leaking and causing a misfire. If the motor is running good then that is not the case.

There are tests for the egr so if you do let me know.

jlsmi2

it's a b18c1 (94 GSR) so yes, I believe it has an EGR valve. the NOx is high, but the CO & HC were within the correct parameters.

* also, it did not appear to have any exhaust leaks. The timing was slightly retarded so I'm going to set it to 12 degrees. I'm not sure that this will really make a huge difference, though it will make it a bit more rich, which should help some.

what else could make the NOx high, while the CO & HC were okay?

jlsmi2

actually, after doing a few searches it looks like my car does not have an egr valve as it is not pre-94.

next...

jlsmi2

Will detarding (for lack of a better word) my timing improve this issue?

or is it basically the o2 sensor?

thesmogman

You have advance and retard one or the other. So your spec is 12btdc. To lower Nox it would be retard. There is a limit of + or - 2 degrees so I would go with 11, or 10btdc. You go too far and everything will be off.

thesmogman

Back again just had a run of customers.

So I just re-read your post. You have had the carsound cat for three years, or is it six? Either way my experiences with hi flow cats are that they don't last that long. Usually two smogs or three years.

If your timing was retarded when you took the test then well the timing isn't gonna help.

My feeling is that it is the cat. All of your numbers are up like I said before.

Your HC should be 50 or below. CO should be 0.0 or close to it. And Nox should be under 300 with a good cat and O2 sensor. Now you see why I say your numbers are up.

jlsmi2

I believe the cat about 3 years old.

I think it was at 13 or 14 degrees. If I were to set it at 11 or 10 as you suggest, or even 12, is there any chance that would make enough of a difference to pass?

seems like probably not.

so you guess cat and not o2 sensor bc of the increase in the HC and CO over time?

-- I'd love to pinpoint which is defective so I only replace the part that needs replacement.

I also plan to do an oil change and tune up, but like the timing I can't imagine that would make an incredible difference.

thesmogman

My real results were...

My Spec is 18btdc I set it at 19 (1 degree advanced)and the results were.

HC 34
CO .1
Nox 354

Then I set it to 17btdc (1 degree retarded) and

HC 30
CO .0
Nox 98 (a 250ppm drop)

If you were at 14 then it might just get you to pass.

jlsmi2

That's a big difference. I will adjust this week and see how that goes.

Thanks for the advice.

garyhgaryh

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jlsmi2 &raquo;</TD></TR><TR><TD CLASS="quote">Will detarding (for lack of a better word) my timing improve this issue?

or is it basically the o2 sensor?</TD></TR></TABLE>

Yes, retarding the timing will help reduce Nox.

That's how I passed in Aug.
Gary