Help: Failed NOx test in MA 1990 300SE

Good Old MA dyno testing gets me

Grams Per Mile
Reading Limit
HC 1.06 2.00
CO 5.86 30.00
NOx 4.17 3.00
CO2 359.26 N/A

Car Details:
1990 300SE 228,000 Miles
Car was running hot little over 100C
Only had mid grad gas in it 89 octane
Car sat idling for 5-10 mins before being tested

Cap, rotor, plugs, wire, filter, EGR valve replace less than 30,000 miles ago
Cat. was replaced back in 96 or so at 70,000 miles

Does the car need a new cat. system?

Or should I retest using premium gas and when it is running cooler and not allowed to idle so long before the test?

I have one more shot before I have to pay another 29 bucks.

Thanks
Dan

 

Sleepwalker would probably be able to answer this question for you better than I, but I would say that using premium gasoline would definately improve your emmisions. Your car's timing is set to be optimally adjusted to 92 octane gasoline. Also, you might want to check and make sure that your idle is set right. The lower the idle is, the more advanced the timing will be. I don't really think you need a new cat, even with the high miles, since you had it replaced once already. they usually stand up to a lot of milage. I'm still on my same one and it's had over 240,000 miles.

 

also, you should check the vaccum diagram sticker on the ledge in the front of the hood to make sure all your hoses are hooked up right. there's only a few, and it's possible that when the egr valve was replaced, something got hooked up wrong. the hoses are usually made of plastic and can be told apart by strips of color marked on them.

 

NOx can be formed by many component failures and system malfunctions - anything that allows the combustion chamber temperature to exceed 2300 degrees Fahrenheit. For example, if the cooling system is utilizing pure water, it will absorb combustion heat and obtain its boiling point rapidly, leaving an air pocket around the combustion chamber. The air pocket will become a hot spot allowing for the combustion chamber temperature to rise. Equally bad is 100% antifreeze, which forms a blanket around the combustion chamber, keeping heat in and allowing the combustion chamber temperature to rise. Rust surrounding the cooling jacket surface will create the same blanket around the combustion chamber. Poor flow through the radiator, as a result of a blockage or poor circulation, or a partially closed thermostat or limited flow from the water pump, will prevent the high temperatures from escaping through the cooling system. This temperature increase will cause preignition, allowing the oxygen to prematurely oxidize the hydrogen, reducing the available air and fuel during spark ignition. As a result, oxygen will be limited to complete the oxidation of the hydrogen and formation of carbon and oxygen into carbon dioxide will be limited. In this case the gas meter will read high HC, low CO, low 02, low C02, and high NOx

You can considering replacing the catalyst too.

 

Thanks for your help. I will check the lines going to the EGR and check the EGR itself. Also I will get the aux fans working again as the car was running hot. Might change the spark plugs too and will run 92 octane gas.

I will post the results.

 

Hi Cam, did you ever resolve the issues regarding your failed attempts to get the 300se through MA Inspection?

Please let me know the Fixes ,as i have similar situation with my 89' 300se down here in NJ.

Regards,
Geordie.