Air Injection: Description and Operation

GF14.30-P-3012MOS Air Injection, Function
ENGINE 275.953 in MODEL 216.376, 221.176 as of Model Year 09 /AEJ 08
ENGINE 275.982 in MODEL 216.379, 221.179 as of Model Year 09 /AEJ 08

Function requirements for air injection, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Coolant temperature greater than 10°C and <35°C
^ Engine speed <2500 rpm
^ Engine at idle or partial load operation

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

The ME-SFI control unit (N3/10) manages the air injection according to the information from the following sensors:

- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8) and pressure sensor downstream of throttle valve actuator (B28/7), engine load
- Crankshaft position sensor (L5), motor speed

The injected air reacts with the hot exhaust gases in the outlet ducts and firewall catalytic converters. Oxidation of carbon monoxide (CO) and hydrocarbons (HC) takes place (afterburning).
This afterburning leads to a further increase in the exhaust gas temperature (exothermic reaction), which additionally heats the firewall catalytic converters.

Air injection function sequence
Injected air is supplied by the electric air pump (M33), which is actuated through the air pump relay (N10/1kA) by the ME-SFI control unit.

If the air pump switchover valve (Y32) is actuated by the ME-SFI [ME] control unit at the ground end, it connects the vacuum from the intake manifold to the air shutoff valves. This opens and the injected air is blown from the electric air pump into the exhaust ducts of the cylinder heads.

To provide the air injection, both the air pump switchover valve and the electric air pump are actuated by the ME-SFI control unit for up to 90 s.

Following actuation, air injection remains locked. Air injection is only enabled again if the coolant temperature rises above 60 °C and then falls below 40 °C. The electrical air pump also has sufficient time to cool down again.

Diagnosis
For diagnosis with the Diagnosis Assistance System (DAS), air injection should be enabled for up to 120 s (less than this if the engine is warm).
Prior to the next actuation, it is essential to maintain a cooling time of 30 minutes, otherwise the electric air pump may be damaged (overheated).