Air Injection: Description and Operation

GF14.30-P-3012MIG Air Injection, Function
ENGINE 272.945 in MODEL 251.054 /154 as of Model Year 2009 /AEJ 08
ENGINE 272.967 in MODEL 164.186 as of Model Year 2009 /AEJ 08 MOPF
ENGINE 272.967 in MODEL 251.056 /065 /156 /165 as of Model Year 2009 /AEJ 08
ENGINE 273.923 in MODEL 164.871 as of Model Year 2009 /AEJ 08
ENGINE 273.963 in MODEL 164.172 as of Model Year 2009 /AEJ 08 MOPF
ENGINE 273.963 in MODEL 164.886, 251.072 /172 as of Model Year 2009 /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
^ Coolant temperature greater than 7 °C and <35 °C (with code (494) USA version)
^ 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:

- Hot film MAF sensor (B2/5), engine load
- Coolant temperature sensor (B11/4)
- Crankshaft Hall sensor (B70), 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
The injected air is supplied by the electric air pump (M33), which is actuated by the ME-SFI control unit through the air pump relay (F58kE).

If the air pump switchover valve (Y32) is actuated by the ME-SFI control unit at the ground end, it switches the vacuum from the variable 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 40 s.

Following actuation, air injection remains locked. Renewed enable of air injection will only take place if the firewall catalytic convertors cool down again due to a sufficiently long stoppage time of the engine. 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).