high @ about 1600. The mech says I need egr valve but I don't see one listed at Fastlane. Does my car indeed have this valve and are there any other fixes I should look at to pass the test?

i am not sure if that model has one, but if it does it will be on the drivers side exhaust manifold. it may be something besides the egr valve so check basics before you buy a new valve, send me your vin number, i will see what the parts guide shows. also was the tech you spoke with a licensed smog tech?

If you wish to receive any meaningful help from this forum, you need to post all the gas analyser results from your test. Also, look at the emission/tuneup decal in the engine compartment and list all the emission control system codes.

Duke

NOX or nitrogen oxides typically elevate when combustion temperatures are high. This actually results in better performance and efficiency, but also exceeds NOX levels. EGR (exhaust gas recirculation) is used to "cool" the mixture down by replacing some of the volatile gas/air mixture with exhaust gas. A failure of the EGR valve to open, or carbon deposits in EGR ports are a common cause of high NOX. If the Mercedes does not have an EGR system, then something else is used to cool the mixture during acceleration and high speeds. I am not familiar with the system on this car , but maybe this helps find the source of the issue. Good luck.

I have had 2 1984 380 SEs fail the MA NOX test. When the timing was retarded fro the test, the results were compliant. Prior to this I was told I needed a new catalytic converter....that did nothing to change the bad results.

I'll probably catch some flack from a poster, because it goes against scientific theory, but as an electronics technician for ten years in a previous life, I learned it is just theory. At any rate a guy who lives in the south bay had the same problem on about the same car. As he and the mechanic were cruising the Santa Cruz Mountains, he noticed the temp was running high. The radiator was changed for suspected restricted flow. That not only solved the heating problem, but NOX went from 800 ppm to way less than 100 ppm.

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