I went to emmissions and everything passed except NOx reading. It came in at 3.17 and Colorado only allows 2.0. I took it home and replaced the egr valve, air filter and changed the oil. I then added two bottles of the lucas Nox reducer and ran thru a tank of gas. then before I went to emmissions the second time I ran the car for about 30 miles to make sure catalytic converter was nice and hot. NOx cam it at 3.16. Still no check engine light and vehicle seems to run good. What can it be?
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Are all the error codes ok? Sometimes a minor code will not cause a "check engine" light on the dash. If the ignition system is marginal it will continue. The results of the emmission test help diagnose. Usually Nox is too high. It's usually caused by a very high temp combustion temperature. Carbon buildup in the cylinder may cause. If the cooling system is marginal, it may contribute. Some advocate a decarbonizing effort. Double check all your connections, cleaning and scraping to bright metal may help. I found a disconnected ground wire. It seemed to make the difference between pass and not.
Your uncle could be right. It is always best to make sure you put the correct fuel for your make and model in the tank. Don't put in any additives unless approved by the vehicle manufacturer. The catalytic converter in the exhaust system is what reduces the CO and NOX in your exhaust. It has a catalyst in there which causes certain chemical reactions in the exhaust. Firstly the converter must reach operating temperature, so before you get the exhaust checked make sure your cars exhaust is nice and hot, a five minute drive up to the inspection station first thing in the morning may not get the converter to the operating temperature. The other problem may be as your uncle said. The injector cleaner may have put out certain chemicals into the exhaust that have put a fine layer of residue in the converter. This will block the NOX from getting to the catalyst and therefore stop or lower the reduction. You may have to replace the converter (they are expensive here in Australia) but you should try and take the car for a long easy drive in the hope that it will burn off the residue (if there is any in the converter) and then go and have the levels checked, the converter should be hot enough to do its job by then. You may also want to try another inspection station on the other side of town or another town depending on the distance, that will get the converter to operating temperature and the inspection stations meter may be calibrated better than the one you are going so it will give a better reading!
fist i would like you to post the year make and model of the truck along with the HC ppms and NOX ppm it would be very helpful but high hc and nox can be attributed to a faulty EGR system nox is produced when the combustion chamber temperature gets too high so a small amount of exhaust is cycled back into the air stream to help cool them there are other causes but without looking at the levels its much harder to say
here are the possible causes of high nox levels, Misfire condition Malfunctioning or improperly adjusted EGR valve Failed
oxygen sensor Leak in exhaust tubing upstream of converter Excessive
carbon deposits in combustion chamber Improper spark advance Blocked
coolant passage Overly lean air-fuel mixture Damaged cold air
duct Failed or malfunctioning catalytic converter Corroded or damaged
engine sensor electrical connections.the best advice is to take it to a emission specialist to check it out! good-luck!
NOX is usually something like an EGR Valve or engine overheating,at least in the inspection lane.
I don't have the code, but you can see if the Egr is working and pull it off to make sure the passages are clean.
Going to inspection on a cool day helps, and don't sit there idling,shut it off.
The catalytic convertor could be the issue. A car in bad need of a tune-up won't usually pass smog, either. High emmissions is caused by either a bad cat or unburnt fuel. Start looking at the ignition system (spark plugs, plug wires) and give that thing a tune-up.
the car is older that 1996 there for you dont need emissions testing. if you wish to pass, check the carbon canister and the egr valve. if the temp gauge says the cars not over heating and the engine doesnt appear to be hot, dont worry about it.