The exhaust emission control system, is the last line of defense, against harmful hydrocarbons (air pollution).

So, any shortage of spark or if the spark occurs, at the wrong time. Then, incomplete combustion and higher hydrocarbons will result.

The exhaust emission control, consists of three additional systems. The secondary air injection system, the exhaust gas recirculation (EGR) system and finally the catalytic converter.

Consequently, all parts of the exhaust emission control system, need to work together. Because, only then can they provide, a good defense against overall air pollution.

Catalytic Converter

So, by cleaning up the pollutants left over from combustion, they reduce exhaust emissions. In addition, to hydrocarbons (HC) and carbon monoxide (CO).

Exhaust Gas Recirculation (EGR) (exhaust emission control)

So, exhaust gas recirculation, reduces the formation of NOX. Consequently, by letting a small amount of exhaust gas, to “leak” into the intake manifold. The amount of gas leaked into the intake manifold, is only about 6 to 10% of the total. But, it’s enough to dilute the air/fuel mixture, just enough to have a “cooling effect” on combustion temperatures. This keeps combustion temperatures below 1500 degrees C (2800 degrees F). As a result, to lower the reaction, between nitrogen and oxygen that forms NOx.

Secondary Air Injection System (exhaust emission control)

So, with spark-ignition engines, the greatest pollution occurs on cold starting. Therefore, secondary-air systems have been successfully employed, to reduce such cold starting emissions. The secondary air injection pump, is responsible for pumping fresh air from outside, into the exhaust stream.


Choose Your Exhaust Emission Control Help Topic Below

Air Injection – Secondary Air Injection System – Types – Function – Failure

(EGR) Valve – Exhaust Gas Recirculation Valve – What Should You Know

Exhaust Gas Recirculation (EGR) Valve – Types – Failure – Replacement

Engine Problems – What Are The Most Common, Engine Problems

Catalytic Converter – Knowing The Basics And Testing

Exhaust Emission Control Thermactor Plugs – Needed For Small Block Ford Cylinder Heads

(O2) Oxygen Sensor – Function – Failure Symptoms – Testing

(EGR) Valve – Is the problem your (EGR) valve or is it something else.

Oxygen Sensor (O2) – What Else Could Cause Rich Or Lean Codes

(O2) Oxygen Sensors – Function, Failure Symptoms, Testing Procedures


Thank You !