Fuel System - Onan DJA Series Operator's And Service Manual

FUEL SYSTEM
The diesel fuel system provides a means of filtering,
transporting and delivering fuel in a fine spray to the
engine cylinder at the correct time for ignition. The
system consists of a primary fuel filter, fuel transfer
pump, secondary fuel filter, injection pump and an
injection nozzle. See Figure 11.
The diaphragm fuel transfer pump which operates direct-
ly off the engine camshaft, draws fuel from a supply
tank and delivers it through two filters to the injection
pump. The injection pump meters fuel and delivers it,
at high pressure to the injection nozzle at the correct
time for ignition.
The injection nozzle opens at a set fuel pressure, de-
livering fuel in a fine spray, to the precombustion
chamber for ignition. The nozzle remains open, deliver-
ing fuel as long as the fuel pressure remains above
the critical point.
Extra fuel is bled off after each injection cycle by a
fuel return line from the nozzle. An adapter combines
the leakoff fuel with the flow-through fuel from the
injection pump. A return line connected at this point,
returns the combined fuel back to the fuel supply tank.
AIR
C L E A N E R
M A N I F O L D
H E A T E R
G L O W P L U G
C R A N K C A S E
B R E A T H E R T U B E
F U E L
R E T U R N LINE
FUEL F I L T E R
S E D I M E N T
B O W L
P R I M A R Y
F U E L F I L T E R
I N J E C T I O N
N O Z Z L E
I N J E C T I O N
P U M P
S E C O N D A R Y
F U E L FILTER
F I G U R E I I . D I E S E L F U E L SYSTEM ( B E G I N N I N G
WITH SPEC S)
Dirt in the fuei system is a diesel
, engine's worst enemy. It is one of the
major causes of diesel engine failure. Even a tiny piece
of dirt in the injection system may stop your unit. When
opening any part of the fuel system beyond the second-
ary fuel filter, place all parts in a pan of clean diesel
fuel as they are removed. Before installing new or used
parts, flush them thoroughly and install while still wet.
MAINTENANCE
, In addition to regular service periods, change the
secondary fuel filter cartridge if the engine shows
signs of starving from lack of fuel. Remove the second-
ary filter by removing the large cap screw in the center
of the filter cover. Use care when replacing the filter
cartridge to avoid getting dirt into the injection pump
passages.
When replacing or cleaning filters, bleed the fuel
system. Do this by opening the air bleed screw located
on top of the secondary filter removal cap screw. Oper-
ate the hand priming lever on the transfer pump until no
air bubbles flow from the bleed screw hole, then
tighten the bleed screw. Return the priming lever to its
original position. See Figure 12.
IMPORTANT: // the transfer pump cam lobe is on the
high side, the priming lever will not operate the pump.
Turn the engine one revolution beiore operating the
priming lever.
F U E L TRANSFER PUMP
The transfer pump is located on the left side of the
engine. If fuel does not reach the secondary filter,
make the following checks before removing the pump.
1. Check the fuel tank and see that the shutoff
valve is open.
2. Remove the fuel line from the transfer pump outlet
and work the priming lever on the pump. Fuel
should spurt out of the pump. If not, remove the
pump for repair or replacement.
Testing: If the transfer pump delivers fuel, test it with
a pressure gauge or manometer. Perform these tests
before removing the pump from the engine. Remove the
pump outlet and install the pressure gauge. See Figure
13.
Test the valves and diaphragm by operating the primer
lever a few times and watching the pressure. It should
not drop off rapidly after priming has stopped.
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