GMC 4000 Series Service Manual page 360

Stam ped
T-65
Figure 3 — Primary Fuel Filter (Typical)
2. Loosen bolt at top of filter until shell and
element can be removed.
3. Lift element from shell and discard.
4. Wash all parts with solvent to remove all
accumulated matter.
5. Install new element in shell then position
element and shell assembly to base using gaskets
furnished with new element. Fill shell with fuel.
6. Tighten cap screw securing shell in place.
Check filter connections and fuel lines for leaks
and tighten if necessary.
SECONDARY FILTER
Frequency of changing the secondary filter
must be established by experience gained in actual
operation of vehicle. Filter is illustrated in figure
4, Item 7.
Regular filter replacement intervals should not
exceed 10,000 m iles. Under the most severe con­
ditions filter should be replaced every 6,000 m iles.
F ilters should also be replaced whenever a p res­
sure drop across the filter reaches 15 psi before
the 10,000 m ile replacement.
Secondary filter can be checked as follows:
1. Clean all accumulated particles of dirt
from fittings and lines at top of secondary filter
and fuel line junction at left side of fuel injection
pump housing.
IMPORTANT: Every precaution must be taken
to prevent dirt from entering fuel passages as fuel
lines are disconnected and test equipment is in­
stalled.
G M C S E R V I C E M A N U A L
1 Fuel Injection Pump 5
2 P ressure Gauge
3 Secondary F ilter
4 Secondary F ilter
top of secondary filter and install pressure gauge
which is part of testing set (J-21731) (fig. 4).
disconnect fuel line, and assem ble adapter fitting
(9, fig. 4) and pressure gauge (also part of set
mentioned in previous step 2).
sembled in lines*
remain loose enough to bleed out any air, and al­
low engine to idle until fuel begins to flow, then
tighten the fittings.
the two gauges (fig. 4). Normal pressure on gauge
(5) in filter inlet line should be 40 to 50 psi. If
secondary filter is in satisfactory operating con­
dition, the reading on gauge (2) will show approx­
imately
gauge (5). If the pressure drop (differential) is
greater than 15 psi between the two gauges, a par­
tially clogged filter is indicated and the secondary
filter assembly should be replaced.
gauges and adapter fittings and connect fuel lines
in original position, bleed out any air which may
have been trapped in lines, and inspect line con­
nections for leaks. If test has indicated need for
secondary filter replacement, follow the instruc­
tions given below to install new filter assembly.
REPLACING SECONDARY
FUEL FILTER ASSEMBLY
ENGINE FUEL SYSTEM— DIESEL
P ressu re Gauge
6
Gauge Adapter Fittings
7 Secondary F ilter
Outlet Line 8 Fuel Pump
9 Gauge Adapter Fittings
Inlet Line
Figure 4 — Testing Secondary Filter
2. Disconnect fuel flexible line from fitting at
3. At fuel injection pump supply line fitting,
Refer to figure 4 for view of test gauges a s­
4. Allow adapter fittings (6 and 9, fig. 4) to
5. With engine running, observe pressures on
psi lower reading than that shown on
5
6. After completing pressure checks, remove
Key numbers in following text refer to figure 5.
1. Clean accumulated dirt from fittings at top
Sec. 6M
Page 349