Nitrous Oxides

My Mitt. Montero just failed emissions test for Nitrous Oxides can anyone help with possible causes and how I can get them lower??

I don't think you mean nitrous oxide...that's a power booster used in some cars. You may mean sulfer oxide, or NoX (I can't remember what it stands for at the moment) which are emissions related gases.
How many miles on the car? A new catalytic converter could help, if not solve the problem.

Yup, oxides of nitrogen. They are a greenhouse gas and contribute to acid rain.

I would consider an upper engine cleaning. There are several ways of doing this, but one of the more effective is using a product from GM. You'll probably have to get some from a GM tech since its not an over the counter thing. Anyway, you pull a vacuum line, stick it in this bottle, and it sucks up a solvent that cleans carbon out. It worked on my buddy's F150 anyway.

Another way is to run the engine at a fast idle and spray squirts of water in the intake from a spray bottle. Not sure of your particular application, but you might want to take the ducting off up to the MAF so you can direct the water around the delicate wire in the sensor.

Replace your plugs with a cooler heat range. A good parts guy will know what you're talking about.

Again, not sure of your year and setup, but double check the timing and make sure its spot on.

Typical causes of high NOx are increased compression/altered combustion from carbon buildup, timing too far advanced, bad plugs or plugs that are too hot, or a mixture that is too lean.

You might be able to slip by emissions by using a tank of premium fuel, but its not likely. I would hate to advise that and then just have you fail again.

I don't think you mean nitrous oxide...that's a power booster used in some cars. You may mean sulfer oxide, or NoX (I can't remember what it stands for at the moment) which are emissions related gases.
How many miles on the car? A new catalytic converter could help, if not solve the problem.
there is 200,000 miles on the car rebuilt engine at 189,000 NoX is almost double max allowed. all other emissions were quite low

Yup, oxides of nitrogen. They are a greenhouse gas and contribute to acid rain.

I would consider an upper engine cleaning. There are several ways of doing this, but one of the more effective is using a product from GM. You'll probably have to get some from a GM tech since its not an over the counter thing. Anyway, you pull a vacuum line, stick it in this bottle, and it sucks up a solvent that cleans carbon out. It worked on my buddy's F150 anyway.

Another way is to run the engine at a fast idle and spray squirts of water in the intake from a spray bottle. Not sure of your particular application, but you might want to take the ducting off up to the MAF so you can direct the water around the delicate wire in the sensor.

Replace your plugs with a cooler heat range. A good parts guy will know what you're talking about.

Again, not sure of your year and setup, but double check the timing and make sure its spot on.

Typical causes of high NOx are increased compression/altered combustion from carbon buildup, timing too far advanced, bad plugs or plugs that are too hot, or a mixture that is too lean.

You might be able to slip by emissions by using a tank of premium fuel, but its not likely. I would hate to advise that and then just have you fail again.

thanks for the advice the suv has over 200,000 miles but engine was rebuilt at about 189,000 all other emission were quite low

If I recall correctly excessive NOX production can be caused by too high of a temperature of combustion and one of the causes is the EGR system. The EGR valve routes exhaust gases into the intake stream and lowers combustion temperatures. If I am correct I would recommend cleaning and ensuring the EGR valve is operational.

Excellent catch, DRW1000. I totally forgot about the biggest one; EGR valve.

If I recall correctly excessive NOX production can be caused by too high of a temperature of combustion and one of the causes is the EGR system. The EGR valve routes exhaust gases into the intake stream and lowers combustion temperatures. If I am correct I would recommend cleaning and ensuring the EGR valve is operational.

Yeh I remember hearing a while back that your cat converter creates very small amounts of N02; I was thinking.... Afterburner!!! :smokin:

i would recommend removing the EGR and cleaning it, i would use sensor safe carb and choke cleaner. most likey the EGR gasket will need replaced as well. also inspect and clean the vacuum lines and solenoid if it is a vacuum controlled EGR

There are several ways of doing this, but one of the more effective is using a product from GM. You'll probably have to get some from a GM tech since its not an over the counter thing.

you should be able to buy GM Top Engine Cleaner at the parts counter of any GM dealership. P/N 1050002 for the 15 Fl. Oz can, but i beleave it also comes in other sizes.

A new catalytic converter could help, if not solve the problem.

a Two-way catalytic converter does not effect NOx, a Three-way cat does reduce NOx.