TM 5-3895-359-14&P
PRESSURIZE FUEL SYSTEM CHECK FOR LEAKS
Always check the fuel system for leaks after injector or
After maintaining 40-80 psi (276-552 kPa) for 20 to 30
fuel pipe replacement and any time the fuel connections
minutes, a careful puddle inspection should reveal any
under the rocker cover are suspected of leaking. Failure
suspect connectors. Inspect and repair or replace
to correct a serious fuel leak in this area can lead to
connectors as necessary. Test and reinspect (see note).
dilution of the lube oil and bearing and/or cylinder kit
damage.
Method 3. Use while the engine is operating at 400600
rpm.
Prime and Purge
Apply an outside fuel source capable of 60-80 psi (413-
Prime and/or purge the engine fuel system before
552 kPa) to the outlet side of the secondary filter. Pour
starting the fuel leak check. Prime the system by
lube oil over jumper lines and connectors so that oil
blocking or disconnecting the line from the fuel pump,
puddles form where lines and connectors meet. Install a
then apply fuel under pressure (60-80 psi or 413552
valve and a pressure gage in the fuel return line. With
kPa) to the inlet of the secondary filter. If the system is
the engine idling, close the valve enough to raise the
to be purged of air as well, allow the fuel to flow freely
engine fuel pressure to 70 psi (483 kPa). After 10 to 20
from the fuel return line until a solid stream without air
minutes inspect the oil puddles to see if any have
bubbles is observed.
become smaller or run off completely. The undiluted oil
will hang the same as when the oil was poured on.
Check for Leaks
Repair and retest.
Use one of the following methods to check for leaks.
NOTE: With the engine at rest, as in Method 2 all
injectors will leak to some extent when pressurized. The
Method I. Use when the engine has been operating 20-
leakage occurs because there is no place else for the
30 minutes.
pressurized fuel to go. When the low and high pressure
cavities in the injector are subjected to the high test
After operating the engine, shut it off and remove the
pressure, fuel is forced past the plunger into the rack
rocker covers. Inspect the lube oil puddles that normally
and gear cavity. Result: Droplets of fuel form at the
form where the fuel connectors join the cylinder head
rack and drip off.
and where the fuel pipes join the fuel pipe nuts.
Slightly worn plungers may leak more under these
If there is any leakage at these connections, the lube oil
conditions. This leakage will not occur while the
puddles will be smaller or thinner than the puddles on
engine is running because of the dynamic and
the connectors that are not leaking. Disassemble,
pressure conditions that exists.
inspect and correct or replace the suspect part
(connector washer, connector, injector or jumper line).
If injectors are suspected of leaking and
Test and reinspect.
contributing to dilution of the lube oil, they should
not be tested by pressurizing the fuel system as in
Method 2. Use when the engine is not operating such
Method 2. Injectors should be removed from the
as during or after repairs.
engine and tested for pressure-holding capability
(see Fuel Injector Section).
Remove the rocker covers. Pour lube oil over all fuel
pipes and connectors which would normally be splashed
Points to Remember
with oil during engine operation. This will cause oil
puddles to form at the joining surfaces as mentioned in
Lube oil puddle inspection is the key to pressure testing
Method 1.
the fuel system for internal leaks. This test can be
performed any time the rocker covers are removed,
Block off the fuel return line and disconnect the fuel
after the fuel pipes and connectors have been splashed
pump supply line at the secondary filter. Install a
with oil and there is normal fuel pressure in the system.
pressure gage in the filter adaptor, then apply 6080 psi
The weak or missing puddles show where the leaks are.
(413-552 kPa) fuel to the outlet side of the secondary
filter with the inlets plugged. Severe leaks will show up
All leakage or spillage of fuel during leak detection
immediately. Minor leaks caused by nicks or burrs on
testing further dilutes the lube oil, so the final step in
sealing surfaces will take longer to appear.
maintenance of this type should include lube oil and
lube oil filter changes.
10-3-56
