KA24E Emission Test Failed

[DeltaZulu]

My 1990 240SX 5SP failed Illinois emission test for high HC (Standard 0.8 GPM and Reading was 1.55 GPM). In the test result, I do not see any relation with rpm and the amount of HC.

Check Engine Lamp was on and off and after self-diagnosis with ECU, it showed code 31 (ECU faliure - I am not 100% sure because it took a while for LED to turn on). I am wondering if ECU was the cause of the problem and replacing ECU will reduce HC.

From carfax record, I learned that previous owner also failed the test (with old engine- 165K on it and with ex-valve failure). When I bought this car, I replaced the engine to 1989 model (85K on it) and is running great.

I checked all emission control related sensors and they all seem right. I do not know if the catalytic converter is failed or not.

If anyone knows possible cause and solution for this high HC, please let me know.

Thank you in advance.

[NISTECH]

ignition would be the primary cause for hc failure. do they measure NOx there too? if so was it high?

[DeltaZulu]

Thank you for your prompt reply.

NOx was measured 7.4 GPM and CO2 was 385.1 GPM. They do not have Standard for these two readings. CO reading was 11.1 GPM with 15.0 GPM Standard.

Thanks,

[NISTECH]

gpm is hard for me to determine how bad it is since here in california we use ppm as measurement

[NISTECH]

usually plugs ,timing, wires ,cap and rotor effect hc. if it were lean i would be able to tell by your NOx percentage as long as it was dynoed

[NISTECH]

hc is raw unburnt fuel. co is partially burnt fuel. co2 is combustion effeciency. nox is the result of high combustion temp and pressure. when a car goes lean the the temp in the cyl sky rockets causeing O2 molocules to combine with nitrogen molocules. which would indicate if the hc's were being caused by a lean misfire.

[NISTECH]

seeing how your co is above 50 % of acceptable amount I would say you could stand to run the car a little leaner. hc and co can go hand in hand. A higher co could indicate a higher volume of fuel entering the combustion chamber then is needed to perform the required driving need. this theroy is no good though in 2 cases low compression and a bad cat. the cat is needed to reduce the slightly higher fuel usege the car needs to assure good acceleration. if the cat were to become weak the mixture it needs to clean would pass right through to the tail pipe. since you are fuel injected adjusting the mixture of fuel is not possible. if you had a bad o2 sensor the co would most likely also fail. a restricted air filter can cause higher co and hc be sure to inspect it.

I dont know if this is helping you or confusing you. but that is the info i can give ya.

[DeltaZulu]

Thanks for you input.

I will check ignition system and timing first to see the combustion. When I installed the used engine, my timing light was working intermittantly so, I will double check. Do you think poor ECU and/or Catalytic are also contributing factors for high HC? Since this car failed the same test previously, I am wondering.

Thanks again.

[NISTECH]

yes on the cat not so sure on the comp though. the co would have failed if it were the ecu I would think. but definitly cat. the cat can easily become weak if a car runs to rich or to lean over a substantial period of time. it will either become coated with carbon from a rich state or melt down under a lean state. If you doubt the reliability of the ecu have a scanner put on it to check for codes. I dont think your local parts store will have a method of pulling codes from your car since its pre OBD II . What you could do is go to a dealer or even a shop with a snap on scanner. and tell them all you want them to do is pull your codes and not perform any diagnostics just so you can look up the codes. tell them you only want them to do that so you dont want to pay full diag time.

[DeltaZulu]

Thanks again.

I will work on it tomorow.

[Trppen37]

also dont forget to run your car "kinda hard" before you go there and get it checked..

[DeltaZulu]

Thanks again for your advice.

I have changed ignition parts (plugs, rotor, and dist cap - wires seem to be OK), and catlytic converter and is ready for timing check now. Plugs are in light brown and combustion seems OK.

The factory manual indicated 15 +/- 2 degrees at 750 +/- 50 rpm. Since high HC is my problem, I am wondering if timing setting of 13 or 17 dgrees affect HC reading.

I am almost ready for retest.

Thanks,