GMC 4000 Series Service Manual page 370

3. If a leak is apparent in the suction lines,
filter or fittings, a sight glass or section of plastic
line may be installed at inlet fitting on supply pump
to determine if air is reaching pump through suc­
tion side of system . If no bubbles are observed
at inlet connection, but continue to be present at
outlet line, a defective supply pump is indicated.
Refer to applicable procedure under "Checking for
Crankcase Dilution" for method of checking and
repairing fuel supply pump assembly.
NOTE: Be sure the fuel filter between fuel
tank and pump is not clogged, and that filter gaskets
are in good condition.
CHECKING FOR INADEQUATE FUEL
PUMP DELIVERY AND/OR OVERFLOW
VALVE MALFUNCTION
If it becomes necessary to check for defective
fuel supply pump and/or overflow valve, proceed
as follows:
1. Make necessary inspection to determine
that fuel filters are not clogged.
2. Remove, clean, and inspect the supply pump
relief valve assembly and spring (9 and 8, fig. 7).
Valve and spring are available for service re­
placement. Install relief valve (9), valve spring (8),
and retainer cap (7).
3. Disconnect lines from overflow valve and
remove the valve assembly from the fuel injection
pump. D isassem ble the overflow valve, inspect
parts (fig. 34). Install overflow valve or parts as
required.
4. Check supply pump pressure as follows:
a. Install pressure gauge in line between sup­
ply pump outlet and secondary filter.
b. Gain access to the fuel return line from the
overflow valve to fuel tank. Install a fuel shut-off
valve at fuel tank or return fuel line in order to
restrict fuel flow momentarily.
c. Open the shut-off valve and then start the
engine. While running the engine at 2400 rpm,
momentarily close the fuel shut-off valve. The
pressure gauge should show between 60 and 65psi.
CAUTION: Keeping the shut-off valve
closed for any period of time can cause
the injection pump plunger to overheat
and seize.
d. If p ressures are appreciably lower than
specified in Step c. previously, the supply pump
should be overhauled or the unit should be replaced
with a new supply pump assembly. Procedure for
removal, overhaul, and installation of fuel supply
pump is explained later in this section of this
manual.
e. Remove shut-off valve and pressure gauge.
G M C S E R V I C E M A N U A L
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
1 Insert Assembly
2 Pin (Pressed into
3 Drive Gear
4 Idler Gear
5 Screws with Lock
CHECKING FOR CRANKCASE
DILUTION BY FUEL
lubricating oil dilution by fuel as evidenced by ab­
normally high oil level on dip stick, lowered engine
oil viscosity (thinning) or strong fuel odor, the
procedure following may be useful to find where
the fuel is entering. In each case, a procedure is
given to remedy the condition causing the trouble:
Start engine and observe the control unit to deter­
mine if fuel is leaking at that point. If fuel leakage
is occurring, refer to procedure previously given
under "Control Unit Assembly Replacement" and
replace the control unit O-ring seal.
dence of fuel leakage, refer to "Fuel Supply Pump
Replacement" covered later in this section and
remove the fuel supply pump.
sembly and install a compressed air hose connec­
tor in inlet port.
governor shaft through the oil seal (9, fig. 35) to
seal this opening. Use clamp or other means to
hold tool or shaft during test (step c. following).
apply 40 psi of air at pump inlet port, then sub­
merge the pump assembly in fuel. Look for air
6 Gasket
7 Valve Spring Retainer
Item 1)
8 Valve Spring
9 Relief Valve
Washers 10 Pump Cover
Figure 7— Fuel Supply Pum p Components
In cases when there are indications of engine
1. Remove fuel injection pump side cover.
2. If, in preceding Step 1, there was no evi­
a. Plug the outlet opening in supply pump a s­
b. Insert special tool (J-22457) or spare
c. With pressure regulator in air supply line,
Sec. 6M
Page 359
Cap
Assembly
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