D 250 Pickup L6-225 3.7L (1984)
Air Injection Control Valve: Description and Operation
Air Switching Valve
Fig. 4 Air switching valve
1983-84 MODELS
This valve, Fig. 4, used on 6-225 California engines, switches air injection from the exhaust ports to a point further downstream in the exhaust system
after engine warm-up so that air injection will not offset the effect on NOx emissions by the EGR system. When the engine is warming up and NOx
emissions are low, air injection to the exhaust ports is acceptable. However, as the gases become hotter, they tend to oxidize more rapidly by the addition
of secondary air causing an increase of NOx emissions. At the same time, the air switching valve switches the air injection.
A vacuum solenoid signal from the CVSCO or EGR solenoid causes the switching valve to open, allowing air injection into the exhaust ports. When
the CVSCO shuts off vacuum to the switching valve, the valve closes and bypasses most of the air injection to the injection point downstream in the
exhaust system. A bleed hole in the switching valve permits a small amount of air pump air to be injected into the exhaust ports at all times to assist in
CO and HC reduction.
