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

ENGINE 273 in MODEL 463.202 /222 /236 /237 up to 31.5.12 as of Model Year 2009 /YoM 08

Fig 1: Identifying View Of Air Injection

Courtesy of MERCEDES-BENZ USA

Function requirements for air injection, general points

Circuit 87M ON (engine control ON)
Engine running
Coolant temperature T > -10°C and < 35°C (without code (ZU8) USA version)
Coolant temperature T >7°C and < 35°C (with code (ZU8) USA version)
Engine speed n < 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 [ME] control unit actuates the air injection according to signals from the following sensors:

Hot film MAF sensor, engine load
Coolant temperature sensor
Crankshaft Hall sensor, engine 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, which is actuated via the secondary air pump relay by the ME-SFI [ME] control unit.

If the air pump switchover valve is actuated at the ground end by the ME-SFI [ME] control unit, it connects 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 [ME] 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 t = 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).

Component description for ME-SFI [ME] control unit

N3/10

GF07.61-P-6000G