Question about emission test 1

[mdighe]

Hi

I have a 92 honda accord that failed the emission test. The car is very well taken care off (I mean oil change every 3000 miles, all the scheduled maintenance). Never taken it to anyone else but the dealer.

What is surpriseing is that only the NOX failes (1400 instead of 910) but the CO and CO2 were well below the limits (0.02 CO when the limit is 0.71) Same with CO2.

Is it possible to pass the HC test so well but still fail the NOx requirements?

Also any clues what would cause this?

Thanks

 

[ShaunT]

Have you checked the E.G.R.?

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[patprimmer]

Lean mixture or to much advance can send NOx high. It forms when there is enough free oxygen at very high temperatures

Regards
pat

 

[duck0601]

Yes, it is possible to pass on HC and CO but fail on NOx. Pollution control is a balancing act around an Air-Fuel ratio of about 14.5 with NOX increasing on the Lean side and CO-HC increasing on the rich side (as I remember, I can't find my references, but they are on opposite sides).

 

[natewrench]

I had the same problem yesterday on my emissions test. I failed on the NOx as well. The root of the problem is too high of a combustion temp. A properly functioning EGR will lower the combustion temp. I changed to a much cooler SPARK PLUGS. I was running Bosch plugs with two electrodes (they run very hot!). I also added "NOS" BRAND OCTANE BOOSTER to 93 octane gas, making the fuel less combustable. I also played with the vacuum line on the fuel pressure regulator. A richer mixture will result in less NOx and probably more CO (I could afford that on my emissions test).

Mine passed easily today. If what I did didn't work my next idea was to put a resistor on the intake temp sensor to fool the computer to make a richer mixture.

Check out threads on water injection. Some guy made one for $20.

 

[STEVETECH]

BAD EGR VALVE, CLOGGED EGR PORT OR BAD CAT-CONVERTER!!!DO NOT CHANGE OCTANE RATING. DO NOT WIRE IN A RESISTER TO YOUR INTAKE TEMP SENSOR. DO NOT CHANGE SPARK PLUG HEAT RANGE.TRUST ME ,I DO THIS ALL DAY LONG!WILL BE GLAD TO HELP.E-MAIL IF NEEDED.

 

[GregLocock]

You may find the following publication informative

http://www.autoshop101.com/forms/h56.pdf

Cheers

Greg Locock

 

[Azmio]

Mdighe,
Wonder if you make any changes to your engine. The cause can range from many aspects:-
1) Freer flowing air filter
2) Different exhaust manifold or exhaust system
3) Different ignition timing by changing the EC setting
4) Different air to fuel ratio by changing the ECU setting
5) 'Expired' catalytic converter or the cat converter missing the important ingredient.
6) Etc.

Anyway, for engine tuner, it is always difficult to balance between the (HC+CO) and NOx. If you get the AF ratio too lean or the combustion pressure too hot, the NOx will increase but the HC and CO may decreased. You can also do it the other way around and get the NOx okay but the HC and CO to be bad.
The best is to strike closer and closer to the stochiometric mixture in order to get the optimum conversion rate from the cat converter.

AO

 

[enginead]

This is normally due to poor lambda biasing. The closed loop fuelling system is biased slightly rich to ensure that is no NOx breakthrough during closed loop operation. This is because the catalyst efficiency is much less sensitive on the rich side (HC & CO conversion) than on the lean side (NOx conversion). As the catalyst ages (0-100000 miles so yours shouldn't have any issues) the O2 storage capacity drops and exposes any weaknesses in the biasing calibration. Normally there is a rear trim fuelling controller using the post catalyst lambda sensor (which reads <0.45V when lean) to trim the fuelling back to optimum catalyst efficiency. This system then creates long term adaptions that are used when you operate in a specific speed/load window. If there are any errors in the bias or rear trim calibration these adaptions can be false and lead to poor catalyst efficiency. As a short term check I'd get the garage to check, record and then reset the adaption values then test again, other than that you could ask them to check if there are any software updates for your model to address this problem (if it is this you won't be the only one out there and emission issues tend to get dealt with fairly efficiently by the OEMs so as not to attract attention from the authorities, I've been involved in a $13 million recall for emissions problems and it is definitely not a good place to be).

Good luck