GMC 4000 Series Service Manual page 350

The diverter valve (fig. 35) when triggered by
a sharp increase in manifold vacuum, shuts off the
injected air to the exhaust port areas and prevents
backfiring during this richer period.
On engine overrun the total air supply is dump­
ed through the muffler on the diverter valve. At
AIR PUMP
Figure 3 3 — Schematic of A.I.R. System
G M C S E R V I C E M A N U A L
high engine speeds the excess air is dumped through
the pressure relief valve which is part of the air
pump.
entering and damaging the air injection pump, as
back-flow can occur even under normal operating
conditions.
A.I.R. System will effectively reduce exhaust em is­
sions. However, if any A.I.R. component or any
engine component that operates in conjunction with
MUFFLER
FUEL SYSTEM— GASOLINE ENGINES
Figure 3 4 — Air Injection Pump
The check valve prevents exhaust gases from
When properly installed and maintained, the
Figure 3 5 — Diverter Valve
Sec. 6M
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T-5945