why are my Nox emissions too high?

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After suffering a leaky head gasket several months ago, I just finished rebuilding and reinstalling the head on my 1989 Chrysler Lebaron 4-cylinder, 2.5 liter, single-point fuel injected, non-turbo engine. The vehicle has approx. 200K miles. (the odometer is broken) It seems to start and run fine, but it failed to pass a California smog inspection. The NO emission readings of 1181 ppm (parts per million) at 15 mph(1646 rpm) and 1124 ppm at 25 mph(1869 rpm) were above the respective limits of 799 and 738 and way above the average readings of 237 and 199.

Rather than pay a repair shop, I am attempting to diagnose which of the emission control components that affect NO levels is having a problem. The Haynes brand repair manual I bought states that the emission control systems on this vehicle include: catalytic converter, evaporative emission control system, exhaust gas recirculation (ECR) system, heated inlet air system, oxygen sensor, positive crankcase ventilation (PCV) valve, and Single Module Engine Controller (SMEC) information and self-diagnosis system. In addition to these components, the manual points out that there are numerous switches and sensors which provide feedback to the SMEC, such as the A/C cut-out relay, coolant temperature sensor, Manifold Absolute Pressure (MAP) sensor, transmission neutral safety switch, A/C switch, speed control switch, brake light switch, vehicle distance(speed) sensor, throttle position sensor, etc.

At the time the SMOG check was run, the vehicle was unbeknownst to me missing a heated inlet air system connector tube to transfer heated air from the carburetor air heater chamber back to the air cleaner. The technician indicated that the missing tube must be replaced, but implied that this alone would not likely account for the high NO readings. I have since replaced this missing aluminum-coated cardboard, slinky-like, tube.

The only component which the manual specifically mentions affecting NO emissions is the ECR system. I followed the procedure in the manual to determine whether the vertical shaft of the ECR valve moved up and down during engine RPM changes. I put a dab of white-out on the shaft to make it easier to detect motion. Testing seemed to show that the shaft did open during sudden RPM increases, but the upward motion was slight. I am unsure how much motion is normal. A state vehicle inspection website stated, “If the EGR valve is inoperative, a 5-gas analyzer displays high NOx, high HC, low CO, low CO2, and low O2.” The only emission that was above the limit during the smog test was NO, however both HC and CO measurements were about halfway between “average” and maximum. A 2nd website said, “High NOX emissions are almost always due to a defective EGR valve (or some component that controls the operation of the EGR valve). A related symptom that usually occurs when EGR is lost is spark knock (detonation) during acceleration.” Because the EGR valve moved and since the HC level was not excessive and because the engine does not exhibit spark knock, I tend to think the EGR is working.

The website also said that, “A lean air-fuel ratio results in high cylinder temperature and excessive NOx emissions…. A lean air-fuel ratio may be caused by low fuel pump pressure, partially plugged injectors, a vacuum leak, or defective O2, MAP, ECT, or IAT sensors. A lean air-fuel ratio causes high NOx, high HC, high O2, and low CO and CO2.” Because the CO and CO2 were both low during testing, I tend to think that the problem is not one of the above sensors.

I realize that high NO emissions occur when combustion chamber temperatures rise above 2500 degrees F. This car has a fairly new radiator and brand new coolant and thermostat and has always run in the bottom 1/3 of the temperature gauge.

A friend who helped me to disassemble and reassemble the engine said that once after blowing a head gasket he had to replace his catalytic converter due to damage caused by all the water vapor entering the exhaust system. When I check the manual, it only mentioned HC and CO gases being reduced by the catalytic converter; however, the website stated, “A defective three-way catalytic converter may result in high NOx emissions.” Another website stated that 3-way catalytic converters began in 1991, which I hope means that the CC on this 1989 model has not been damaged. How would I test for this?

I am wondering if anyone has any ideas what else might potentially adversely affect NO emissions. I would really appreciate some assistance. Thanks.

Cameron Hess
Santa Ana, California

posted by  Chess

Well, my uneducated guess would be the catalytic converter is either damaged in some way, or it is clogged like crazy and needs to be replaced. My 1990 Beretta's catalytic converter was clogged like crazy. It ran like crap because of it. We replaced it and it ran great afterwards.
As for you, you said it started and ran great, so that would almost put out the chance of an overclogged catalytic converter. I would have to say it got damaged somehow. I have no clue how to check it either.

Boy, if only VWhobo were here... :cry:

posted by  Satty101

My car ('90 taurus) failed inspection because of high NOx emissions, and because of that sole reason alone (just like yours). So to get it to pass, we replaced the catalytic converter, and the Oxygen sensor, went back to get inspected, and it failed again. This time, the numbers were actually WORSE. So if your other emissions (particularly the CO emissions) are normal or below normal, then your cat. converter and O2 sensor are probably good, and replacing them will not do you any good. You are exactly right about the EGR valve. It is what will lower the NOx emissions. My car ( a '90) did not have an EGR valve, because back in '90, emissions weren't that big of a deal, and many manufacturers did not bother putting EGR's on cars. Im not sure what the ECR valve is, or if its the same as the EGR?

So its very likely that you don't have an EGR valve, which will make it virtually impossible to pass the emissions test. Its impractical to install a EGR valve, so they will grant you a waiver. I know the laws are different (and more stingy) in California, but in Texas, if you spend at least $500 towards trying to get the car to pass, they will grant you a waiver, if the problem would cost more than 500 dollars. installing an EGR would cost more than $500, so we spent it on the O2 sensor, and cat. converter. Your best bet is to shoot for the waiver.

posted by  GhettoTaurus

I haven't had a Chrysler since I sold my 1986 Dodge 600 2.2L Turbo in 1990 until my wife bought a 2002 Chrysler Town and Country LXi Here is some general information

The 1990 Chrysler has an EGR valve

movement of the valve stem of a typical egr valve usually is between 1/16 and 1/8 inch. Most cars this will happen when the actuator is under 6 in vacume

The valve will either have a position sensor or an EGR differential pressure switch of some sort to provide EGR flow feedback to the ECM

The vacume supply is usually controlled by some sort of positioner or solenoid valve which opens or closes in response to a signal from the ECM

Check the vacume hoses first. There will be one hose from a vacume source (manifold or throttle body) to solenoid valve and another to the egr valve actuator to the EGR valve from solenoid valve

Your Haynes book will or should give you the keystroke sequance on the ignition switch for retreiving trouble codes. I would pull those codes and see what the electric brain says first while trouble shooting

Haynes should also provide specific procedures for a complete EGR system examination from the solenoid valve an the way to the EGR valve including making sure the diaphram in the EGR hods vacume If you get confused, post back and either myself or someone will try to help. To do these procedures you will need a vacume pump and an electronic volt meter

The ports on these things tend to clog with carbon. Your problem may be as simple as removing the valve and cleaning the ports with carb cleaner. It could also have a cracked tube between the exhaust manifols and the intake. It could be getting a bad signal from the computer, a bad solenoid valve or a bad EGR valve.

Let us know what you find or if you need more help

posted by  tbaxleyjr

I had nigh NOX reading on the test. Changed air filter, oil, thermostat before that, it did not help.
ERG valve does not exist in my car apparently. Shop wanted 95$ for diagnostics, bought a new Oxygen Sensor, NOx dropped from 1700 to 883, passed. I paid 55$ for the sensor.:hi:
Something to consider...

posted by  the ukrainian

The exhaust gas recirculation (EGR) system controls the formation of NOx (Oxides of Nitrogen) emissions by recirculating the exhaust gases into the combustion chamber. NOx emissions increase with higher combustion temperatures. Controlling high combustion chamber temperatures will limit the formation of NOx emissions. Mixing exhaust gases with the incoming air/fuel mixture modifies the combustion process, resulting in lower combustion chamber temperatures. The EGR system lowers combustion chamber temperatures by admitting controlled amounts of exhaust gas into the intake manifold

posted by  davies

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