Fuel System - Onan DJBA Series Operator's/Service Manual And Parts Catalog

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. Figure 1-1 shows the fuel system.
AIR
U CLEANER
J.
MANIFOLD
HEATER
NJECTION
NOZZLE
GLOW PLUG
CONNECTION
POINT FOR
FUEL RETURN
LINE
INJECTION
PUMP
SECONDARY
FUEL FILTER
INJECTION
NOZZLE
GLOW PLUG
FUEL TRANSFER
PUMP
FUEL
SEDIMENT
BOWL
FUEL FROM
LINE FILTER
PRIMARY
FUEL FILTER
A9I8 R e
FIGURE 11. FUEL SYSTEM
The diaphragm fuel transfer pump which operates
directly 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 pressure, deliver-
ing fuel in a fine spray to the precombustion chamber
for ignition.
Excess fuel is returned to thetank aftereach injection
cycle by a fuel return linefrom the nozzle. An adapter
combines the leak-off 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.
A diesel engine cannot tolerate dirt in the fuel
system. It is one of the major causes of diesel
engine failure. A tiny piece of dirt in the injection system can stop
your unit. When opening any part of the fuel system beyond the
secondary 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 the regular service periods, change the
secondary fuel filter cartridge whenever the engine
shows signs of starving from lack of fuel. Remove the
secondary 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 the filters, bleed the fuel
system. Operate the hand priming lever on the
transfer pump until no air bubbles flow from the
return line fitting of the injection pump. Return the
priming leverto its original position. See Figure 12.
W O R K T R A N S F E R P U M P P R I M I N G LEVER
U N T I L F U E L F L O W S F R O M R E T U R N LINE
F I T T I N G O F I N J E C T I O N P U M P •
FIGURE 12. BLEEDING FUEL SYSTEM
C A U T I O N
If the transfer pump cam is on the high side,
the priming lever will not operate the pump.
Tum the engine one revolution before operating the prime lever.
Starting with Spec S, a new fuel filtration system
accommodates both primary and secondary fuel
filters on a common mounting casting which is bolted
to a newly-designed oil fill tube. Theengine cannot be
run with either filter loose or missing, thus ensuring
proper filtration at all times.
Drain water periodically as required from both filters
and sediment bowl. Replace primary filter every 600
hours and secondary filter every 3000 hours. When
replacing filter, tighten screw until gasket touches
base, then tighten screw 1 to 1-1/2 turns.
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