W250 3/4 Ton Pickup 4WD V8-318 5.2L VIN T 2-BBL (1983)
Pulsed Secondary Air Injection: Description and Operation
Fig. 11 Pulse air feeder system
This system, Fig. 11, used on some 1984---87 models, supplies secondary air into the exhaust system between the front and rear converters. This
action aids oxidation of exhaust emissions in the rear catalytic converter.
The pulse air feeder system consists of a main reed valve and a sub reed valve. A diaphragm, activated by pressure pulses in the crankcase, controls
the main reed valve. The sub reed valve is controlled by pulsations in the exhaust system between the front and rear catalytic converters.