Your EGR may not be working and/or the engine may be overheating. However,
with a reading that high, you may have a problem with the catalytic converter.
Check to see if your EGR is working and check your temperature gauge. If those
checkout, you will proably need a catalytic converter.
Thank you for responding. We can rule out over heating, since the engine is
not over heating. although I did change the thermostat. About two years ago
the NOx was 950, and it is now 1044 and getting worse.
Any idea how I could test the EGR or catalytic converter?
You will need a hand operated vacuum pump. Disconnect the vacuum line at the
EGR and plug it. Attach the vacuum pump to the EGR. At idle when you pull a
vacuum, the idle speed should drop noticeably and increase again when you
release the vacuum. If no change in idle speed the EGR valve is bad.
You should be able to test the EGR valve for leaks if you have a vacuum hand
pump with a gauge. The EGR lowers NOx by recirculating exhaust gas with intake
air. This lowers combustion temperatures and pressures and should lower your
NOx. I understand that you can test your catalytic converter by measuring it's
operating temperature with an infrared thermometer. I've never attempted this
but you might speak to a shop. Since you are in New Jersey, you might contact
Bill Ditmire who has a Mercedes shop in New Jersey. He knows a lot and is
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