What Causes High NO (NOx)?
Nitrogen Oxide or NO is created when an engine's combustion chamber temperature reaches over 2500F. Vehicle manufacturers have designed several systems, which when working properly, lower nitric oxide emissions. Below are common failures which may cause your car, truck, van, suv, or motorhome to produce high high nitric oxide.
1. Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitric oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors.
2. Defective EGR System - The Exhaust Gas Recirculation system is designed to reduce NO. The EGR system consists of an EGR valve, EGR pressure sensor, vacuum hoses, and one or more vacuum switching valves or solenoids. Later model vehicles may be equipped with electronically controlled EGR valves, which do not require vacuum lines or switching solenoids. Electronic EGR systems will have these components built in.
The EGR system's job is to re-route a small amount of exhaust gas back into the intake manifold to help reduce combustion chamber temperatures. As mentioned above NOx is created when combustion chamber temperatures reach above 2500F.
By recirculating exhaust gas back into the intake, a small amount of the air/fuel mixture is replaced with inert gas, reducing combustion temperatures.
3. Defective Catalytic Converter (CAT) Some vehicle manufactures have designed their cars to operate without EGR valves. Non-EGR equipped vehicles rely heavily on the Catalytic Converter to assist in the reduction of NO. These vehicles have tendencies to develop CAT problems sooner then those which are equipped. If you own a non-EGR equipped vehicle, and have failed the emissions test for high NOx, pay close attention to the Catalytic Converter.