Air Injection: Description and Operation

GF14.30-P-3012AMG Air Injection, Function
ENGINE 156.980 in MODEL 164, 251 up to Model Year 8
ENGINE 156.982 in MODEL 209
ENGINE 156.983 in MODEL 211, 219
ENGINE 156.984 in MODEL 216, 221 up to Model Year 8





126/1 Left air shutoff valve
126/2 Right air shutoff valve
128 Vacuum check valve

B11/4 Coolant temperature sensor
B70 Crankshaft Hall sensor
F58kE Air pump replay (model 164, 251)

K17 Air injection relay (model 211, 219)

M33 Electric air pump
N3/10 ME control unit
N10/1kA Air pump relay (for model 216, 221)
N10/1kO Air pump relay (for model 209)
Y32 Air pump switchover valve

A Vacuum supply from the variable intake manifold
B Venting and ventilation of the air pump switchover valve
C Injected air
D Exhaust ducts

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 greater than -10°C and less than 60°C (for (USA) >4°C and less than 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 standstill 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).