Air injection, function - GF14.30-P-3012AMG

ENGINE 156.980 in MODEL 164, 251 

ENGINE 156.982 in MODEL 209 

ENGINE 156.983 in MODEL 211, 219 

ENGINE 156.984 in MODEL 216, 221 

Fig 1: Air Injection, Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The air injection more rapidly warms up catalytic converters to operating temperature after cold starting and thus improves the exhaust emission values in the warming-up phase.

The injected air is made available by the electric air pump. The air pump switchover valve is actuated directly and the electric air pump via the air pump relay/air injection from the ME-SFI [ME] control unit for air injection.

The air injection is actuated by the engine start, if:

• Coolant temperature >-10°C and < 60°C (for >4°C and < 60°C)
• Engine speed < 2500 RPM
• Engine not in full-load range

In order to prevent overheating of catalytic converters the air injection is released just for a maximum of 40 seconds.

After actuation of air injection this remains locked out until the catalytic converters are cooled down again due to an adequately long still stand period of the engine.

Function 

If the air pump switchover valve is actuated by the ME-SFI [ME] control unit it switches through the vacuum out of the variable intake manifold to the air shutoff valves. This opens and the injected air streams from the electric air pump into the exhaust ducts of the cylinder heads.

Functional principle 

The injected air reacts with the hot exhaust gases in the outlet ducts. An oxidation of carbon monoxide (CO) and hydrocarbon (HC) takes place (afterburning).

This afterburning leads to an additional increase of exhaust gas temperature (exothermic reaction), which also warms up the catalytic converters.

Diagnosis 

Air injection can be released for diagnosis with STAR DIAGNOSIS for a max. of 2 minutes (for a warm engine only shortly). A cooling off time of 30 min must be allowed before the next actuation otherwise the electric air pump will be damaged (overheated).