Air Injection: Description and Operation

Secondary Air Injection System:

The M52 is equipped with a secondary air injection system. This system is required to meet the 1996 OBD II requirements for emission control.

The air injection system enables the catalytic converters to achieve operating temperature sooner while burning excess hydrocarbons following cold engine starts.

The system injects air into the exhaust manifolds for defined periods of time. The ambient temperature and engine temperature during the cold start are controlling parameters for air injection operation. Detailed operation of the air injection operation is covered in the MS 41.1 segment of this training program.

The mechanical components of the system include:

Air Pump:

AIR PUMP
The air pump is located in the engine compartment, on the right side, in front of the E-Box. It is a 12 volt DC electric motor driven pump that is controlled by the MS 41.1 control module.

The pump draws filter air through its own air filter and delivers it to both exhaust manifolds through a non-return (shut off) valve.

Non-Return Valve:

NON-RETURN VALVE
The non-return valve serves two functions.

The first is controlling the air injection into the exhaust system. A vacuum controlled diaphragm in the valve will open the passageway for air to be injected when vacuum is applied.

The second function of the valve is to check possible engine backfires from traveling up the pipes and damaging the air pump.

SECONDARY AIR VACUUM/VENT VALVE
The vacuum/vent valve is mounted to the intake manifold next to fuel injector #1. The MS 41.1 control module activates the vacuum valve when the air pump is energized. Vacuum is applied to the non-return valve and air passes through the cylinder head and into the exhaust manifold.

When the vacuum valve is switched OFF, the vacuum in the line is vented to atmosphere and the non-return valve closes.

VACUUM RESERVOIR/CHECK VALVE
A vacuum reservoir and check valve are installed under the intake manifold in the area of the starter. These two components are shared with the MS 41.1 controlled exhaust flap system. The check valve and vacuum reservoir ensures an ample vacuum supply to the valve under all engine operating conditions.