See Figure 1Canadian 240 DL Series With B21A, B23E and B21F Engines
Beginning in 1979, Canadian B21A and some B21F engines were fitted with the (then new) Pulsair air injection system. This system was also incorporated into the Canadian B23E engine in 1983. In the Pulsair system, natural pressure pulses in the engine's exhaust system help to draw fresh air into the exhaust system.
Air is then injected into the end of the exhaust port (as in the air pump system) and the oxygen in the injected air aids in the further burning of emissions. The air pump is eliminated in the Pulsair system. Check valves in the system prevent exhaust gases from entering the air cleaner during the pressure pulses.
To check the operation of the system, disconnect the air hose at the air cleaner. With the engine idling, check that air is being drawn in with the palm of your hand and that no backpressure exists.