GMC 4000 Series Service Manual page 352

AIR MANIFOLD, HOSE, AND TUBE
Inspection (Refer to Fig. 32)
1. Inspect all hoses for deterioration or holes.
2. Inspect all tubes for cracks or holes.
3. Check all hose and tube connections.
4. Check all tube and hose routing. Inter­
ference may cause wear.
5. If leak is suspected on the pressure side of
the system or any tubes and/or hoses have been
disconnected on the pressure side, the connections
should be checked for leaks with a soapy water
solution. With the pump running, bubbles will form
if a leak exists.
Replacement
1. To replace any hose and/or tube, note rout­
ing, then remove hose(s) and/or tube(s) as required.
CAUTION: The !4" pipe thread at the
cylinder head (In-line) is a straight pipe
thread. Do not use a !4" tapered pipe tap.
The hoses of the A.I.R. System are a
special material to withstand high temper­
ature. No other type hose should be sub­
stituted.
2. Install new hose and/or tube(s), routing
them as when removed.
3. Tighten all connections.
NOTE: Use an ti-seize compound on threads of
the air manifold to exhaust manifold or cylinder
head connections.
CHECK VALVE
Inspection
1. The check valve should be inspected when­
ever the hose is disconnected from the check valve
or whenever check valve failure is suspected. (A
pump that had become inoperative and had shown
indications of having exhaust gases in the pump
would indicate check valve failure.)
2. Orally blow through the check valve (toward
air manifold), then slowly attempt to suck back
through check valve. Flow should only be in one
direction (toward the air manifold).
Replacement
Disconnect pump outlet hose at check valve.
Remove check valve from air manifold, being care­
ful not to bend or twist air manifold.
DIVERTER VALVE
Inspection
1. Check condition and routing of all lines
especially the signal line. All lines must be s e ­
cure, without crimps and not leaking.
G M C S E R V I C E M A N U A L
signal must be available with engine running.
should be escaping through the muffler. Manually
open and quickly close the throttle, a momentary
blast of air should discharge through muffler for
at least one second.
Replacement
valve exhaust hose(s).
with new gasket. Torque valve attaching screws to
85 inch-pounds.
check system for leaks.
AIR INJECTION TUBE
Inspection (Refer to Fig. 37)
for the air injection tubes, yet on In-line engines
whenever the cylinder head is removed, inspect
the air injection tubes for carbon build-up and
warped or burnt tubes.
brush.
Replacement
tubes and using penetrating oil, work tubes out of
cylinder head.
FUEL SYSTEM— GASOLINE ENGINES
Figure 3 7 — Air Injection Tubes
2. D isc o n n ec t sig n a l lin e at v a lv e. A vacuum
3. With engine stabilized at idle speed, no air
4. Defective valves should be replaced.
CAUTION: Diverter valves although
sometimes sim ilar in appearance are de­
signed to meet particular requirements
of various engines, therefore, be sure to
install the correct valve.
1. Disconnect vacuum signal line. Disconnect
2. Remove diverter valve from pump.
3. Install diverter valve to pump or bracket
4. Install outlet and vacuum signal lines and
1. There is no periodic service or inspection
2. Remove any carbon build-up with a wire
3. Warped or burnt tubes must be replaced.
1. On In-line engines, remove carbon from
2. Install new tubes in cylinder head.
Sec. 6M
Page 341