GMC 4000 Series Service Manual page 351

Sec. 6M
Page 340
FUEL SYSTEM— GASOLINE ENGINES
Figure 3 6 — Installing Centrifugal Filter
the A.I.R. System should malfunction, the exhaust
em issions might be increased.
Because of the relationship between "Engine
Tune-Up" and "Unburned Exhaust Gases," func­
tioning of the engine fuel system should be checked
whenever the A.I.R. System seem s to be malfunc­
tioning. Particular care should be taken in check­
ing items that affect fuel - air ratio such as the
crankcase ventilation system , the carburetor and
the carburetor air cleaner.
A.I.R. Trouble Diagnosis information is found
at the end of this section.
MAINTENANCE PROCEDURES
DRIVE BELT
Inspection
1. Inspect drive belt for wear, cracks, or de­
terioration and replace if required.
2. Inspect belt tension and adjust if below 50
pounds using a strand tension gauge.
Adjustment
1. Loosen pump mounting bolt and pump ad­
justment bracket bolt.
2. Move pump until belt is tight (55 - 5 lbs.
used belt, or 75 ± 5 lbs. new belt) using a strand
tension gauge, then tighten adjustment bracket bolt
and mounting bolt.
CAUTION: DO NOT PRY ON THE
PUMP HOUSING. DISTORTION OF THE
HOUSING W ILL RESULT IN EX T EN SIV E
DAMAGE TO THE AIR INJECTION PUMP.
G M C S E R V I C E M A N U A L
Replacement
justment bracket bolt, then swing pump until drive
belt may be removed.
lined previously.
DRIVE PULLEY
Replacement
replace drive pulley.
previously.
PUMP PULLEY
Replacement
pressing drive belt, then loosen pump pulley bolts.
then remove pump pulley.
hand tight.
previously.
pressing drive belt, then torque pump pulley bolts
to 25 foot-pounds.
required.
PUMP FILTER
Replacement
cribed previously.
pliers.
ments from entering the air intake hole.
the pulley and pulley bolts (fig. 36).
tightening the bolts. Make certain that the outer
edge of the filter slips into the housing. The slight
amount of interference with the housing bore is
normal.
operation until its O.D. (outside diameter) sealing
lip has worn in.
1. Loosen pump mounting bolt and pump ad­
2. Install a new drive belt and adjust as out­
1. Remove drive belt as outlined above, then
2. Install and adjust drive belt as instructed
1. Hold pump pulley from turning by com­
2. Remove drive belt as instructed above,
3. Install pump pulley with retaining bolts
4. Install and adjust drive belt as directed
5. Hold pump pulley from turning by com­
6. Recheck drive belt tension and adjust, if
1. Remove drive belt and pump pulley as des­
2. Pry loose outer disc of filter fan.
3. Pull remaining portion of filter off with
NOTE: Care should be taken to prevent frag­
4. Install the new filter by drawing it on with
CAUTION: DO NOT attempt to install
a filter by hammering it on or pressing
it on.
5. Draw the filter down evenly by alternately
NOTE: A new filter may squeal upon initial