My 96 camry passed smog a few months ago, passing with wide margins for everything except for NOX. While it passed NOX, it was above the average for NOX. I don't remember the exact value, it was maybe 1/2 of the maximum allowed value.
What could be causing this? Is this a cause for concern?
I have same "generation" '94. Checking smog test results, nitrous oxide max was apx. 700 ppm, avg. apx. 150, and measured results were apx. 50. This was for California. Would guess that means your reading was half the max. apx. 350 ppm? That would be 7X my 50 ppm (parts per million) - for the same engine. Nitrous oxides are created when combustion chamber temperatures pass a certain threshold, so auto makers devised a way to keep the temperatures lower than that level. For your car the solution is "EGR" (exhaust gas recirculation). The EGR system includes a vacuum modulator to vary the amount of exhaust gas recirculated. The idea is that by introducing gases already burned into the combustion chamber, the temperature will be reduced. Since the engine is calibrated with this factor in mind efficiency is not reduced. When I replaced the idle air control valve, the factory service manual included a section for removing and cleaning the throttle body off the car. Along with calibrating the throttle position sensor, was included directions to soak in solvent and blow with compressed air, the three orifices in the throttle body that are uncovered as the butterfly valve progressively opens. These ports lead to the vacuum modulator for the EGR valve. When I hit the smallest port with compressed air after application of solvent, (a tiny pinpoint sized opening) a slug of brownish-black goop was expelled. So you may have something similar. Not sure about the '96, but on the '94 the PCV (positive crankcase ventilation) valve that directs "blowby" gases to the intake, is vented right behind the butterfly valve, very close to those EGR vacuum modulator ports. Also, it is not uncommon for the tube that carries exhaust gases to the EGR valve to become obstructed with carbon deposits. Obviously if the flow of exhaust is restricted, the overall operation of that system is diminished. What to do? Things affect each other in subtle ways. I use the RedLine complete fuel system cleaner continuously. One full bottle, and then a tiny bit with each fuel fill up. RedLine's web site has detailed technical information showing graphs of how carbon is removed from the valve faces over time. RedLine has the distinction of being free of solvents, plus containing a synthetic upper cylinder lubricant. BMW apparently approved this single product for use. I mention this because it survives the combustion process to clean emission control equipment. For example my oxygen sensor still tests out just fine, and it could conceivably help clean the EGR exhaust passageway. You might want to check out auto-rx.com also, regarding cleaning piston ring lands to potentially reduce blow by gasses. The best way to clean the throttle body is by removing and following all the procedures in the manual. Probably couple hundred dollars at the dealer, versus doing it yourself where conceivably cost could be zero, though I replaced the base gasket and coolant, plus purchased a Kragen $99 5 gal. air compressor. The EGR exhaust passage can be cleaned with some sort of wire. Seemed like the best way to access would be to remove the distributor.
Ok, I'll look into this.
I use Red Line fuel treatment every now and then. How much do you mean by "a tiny bit" with each fuel fill up?
Also, is it best to use Red Line with a full gas tank, or with the tank only half full? The Red Line says it treats a full tank, then I saw "10 gal" on the side of the bottle, so I was a bit confused.
For a 2000 I think you don't want anything near 3 digits for NOx. High NOx means your engine combustion temperature is high.
The first thing to check, as said, is the operation of the EGR system. I can send exerpts of my previous posts on the topic. A free loaner MityVac vacuum pump from Autozone used on the EGR valve is a good starting point. Then the cleaning procedure mentioned by Daniel.
Wrong car. ULEVs should be in the low tens for NOx ppm. LEV probably not over 100.
You're supposed to use the amount between the marks on the side of the bottle at each fill up so one bottle treats one hundred gallons of fuel. I've gotten to just letting it go "glug, glug" four times at under one half tank (apx. 10 gallons) or a bit more at quarter tank remaining. I don't think precision is essential here.
You're supposed to use the amount between the marks on the side of the bottle at each fill up so one bottle treats one hundred gallons of fuel. I've gotten to just letting it go "glug, glug" four times at under one half tank (apx. 10 gallons) or a bit more at quarter tank remaining. I don't think precision is essential here, but long term use makes the difference. If you look at their grapsh and charts, can take
10,000 miles for full effect which does improve engine breathing, power and cleanliness.
WHAT!!!? Well thanks for letting me know! I've been using the entire bottle, every time.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.