Air Injection: Description and Operation

AIR INJECTION

DESCRIPTION

Secondary air is supplied to the exhaust ports only during the engine warm up phase. When the engine coolant temperature reaches a pre-determined level, delivery of secondary air is switched from the exhaust ports to atmosphere. This function is achieved by means of a vacuum operated air switching valve, and the vacuum source is controlled by a thermal vacuum valve, located in the right-hand rear coolant outlet rail.

When the water temperature is below 38°C the thermal vacuum valve (5) allows air injection to the cylinder head exhaust ports via the air switching valve (6). When the water temperature reaches 45°C the thermal vacuum valve(5)closes.This causes the air switching valve (6) to switch secondary air from the exhaust ports to atmosphere (air cleaner).

A delay valve (4) is fitted between the thermal vacuum valve (5) and the air switching valve (6) to retain air injection to the exhaust ports during acceleration phases by inhibiting the loss of vacuum from the air switching valve.