ENGINE DIVISION SERVICE MANUAL
Slowly accelerate the engine and observe the speed
at which the test lamp lights. Test lamp should light
above 1850 + 50 RPM.
Slowly decelerate the engine and observe speed at
which the test lamp goes out. Test lamp should go
out below 1850 + 50 RPM.
If test lamp does not function properly, check speed
sensor wiring for proper routing and for clean and
tight connections. If wiring is correct, speed sensor
is faulty and must be replaced. (The speed sensor
and solenoid valve are sold as one assembly.)
AIR INJECTION SYSTEM
Air Injection System Operation
The air injection system forces air into the cylinder
head exhaust ports to promote "after-burning" of any
combustibles remaining in the exhaust gases flowing from the
combustion chamber. The components of the air injection
system are illustrated in Figure 70.
The air pump used in the air injection system is a
rotary vane type which is belt driven from the engine. A
centrifugal type air filter located behind the pump pulley filters
the air entering the pump to prevent entrance of dirt and
abrasives (Fig. 66).
The air manifold distributes air under pressure from the
pump to the individual exhaust ports in the cylinder heads.
Figure 70 shows the location of the air manifolds on the small
V8 engines. The air manifold is an integral part of the MV and
large V8 engine cylinder heads.
A one-way check valve is used on each air manifold to
protect the pump from a back flow of high temperature
exhaust gas. The diverter valve prevents backfire in the
exhaust system by shutting off air flow during the first few
seconds of deceleration. The diverter valve also incorporates
a pressure relief valve which exhausts excessive pump outlet
air pressure during high speed operation. Operation of the
diverter valve is illustrated in Figure 69.
In normal operation (cruising) the air pump delivers air
through the air manifolds into the cylinder head exhaust ports.
With the addition of air from the air injection system, an over-
rich mixture can cause backfire in the exhaust system. To
prevent backfire, the diverter valve momentarily stops the flow
of air to the cylinder head exhaust ports during deceleration.
The diverter valve is controlled by intake manifold
vacuum. At constant manifold vacuum spring pressure holds
the valve in normal delivery position. This permits air to flow
from the air pump to the air manifolds. During deceleration
high manifold vacuum overcomes spring pressure and moves
the valve to bypass position. This closes the outlet port and
bypasses the air flow through the internal silencer to the
atmosphere. The valve returns to normal delivery position
when the vacuum being applied to the diaphragm is balanced
through the orifice to the chamber on the other side of the
diaphragm. Operating cycle time for the valve is
approximately six seconds. In cases of high pump output air
pressure (due to high engine speed etc.), the pressure relief
valve opens and exhausts excessive air flow through the
internal silencer to the atmosphere.
Check Air Injection System and replace, if necessary.
Inspect Air Pump Drive Belt(s)
Air injection pump drive belt tension can be checked
with belt tension gauge SE-2312 (Fig. 64). Check tension at
mid-point between pulleys. Apply gauge to the longest belt
span. Instructions for checking are as follows:
Grasp gauge and depress ball handle all the way
down. Make certain hook extends beyond legs to
pick up the belt.
Apply gauge to belt. Be sure belt is positioned
between nose piece and hook and that the nose
piece is centered on belt.
Release ball handle quickly. A slow release may
present full return of hook, thus giving a false
Observe the area of gauge face indicated at the index
mark. If index mark does not indicate a NEW
reading on a new belt or a USED reading on a used
CGES-215 Page 37
PRINTED IN UNITED STATES OF AMERICA