GMC 4000 Series Service Manual page 353

Sec. 6M
Page 342
FUEL SYSTEM— GASOLINE ENGINES
AIR INJECTION PUMP
Inspection
Accelerate engine to approximately 1500 rpm
and observe air flow from hose(s). If air flow in­
creases as engine is accelerated, pump is operating
satisfactorily. If air flow does not increase or is
not present, proceed as follows:
1. Check for proper drive belt tension.
2. Check for a leaky pressure relief valve.
Air may be heard leaking with the pump running.
NOTE: The A.I.R. System is not completely
n o iseless. Under normal conditions noise rises in
pitch as engine speed increases. To determine if
excessive noise is the fault of the Air Injection Re­
actor System, operate the engine with the pump
drive belt removed. If excessive noise does not
exist with the belt removed, proceed as follows:
3. Check for a seized air injection pump.
4. Check hoses, tubes, air manifolds and all
connections for leaks and proper routing.
5. Check air injection pump for proper mount­
ing.
G M C S E R V I C E M A N U A L
NOTE: Air Injection Reactor (A.I.R.) Trouble
Diagnosis information and Gasoline Engine Speci­
fications are found on the following pages.
6. If none of the above conditions exist, and
the air injection pump has excessive noise, remove
and replace pump kit.
Pump Replacement
1. Disconnect the hoses at the pump.
2. Remove the pump pulley as described pre­
viously.
3. Remove pump mounting bolts and remove
pump.
4. Install pump with mounting bolts loose.
5. Install pump pulley as describedpreviously.
6. Install and adjust belt as described pre­
viously.
7. Connect the hoses at the pump.
8. Tighten mounting bolts securely.
PRESSURE RELIEF VALVE
The pressure relief valve is incorporated in
the diverter valve (see fig. 35). The complete unit
must be replaced to correct a malfunction of the
relief valve.