To
test the solenoid, check plunger operation and
current draw with 12-volt input. Current draw with
the
plunger up should be about 1 amp.
If
it
is much
greater, the contacts did not open.
The solenoid plunger should be adjusted
so
it
fully
stops injection when in the de-energized position. To
adjust the plunger length, turn the screw and jam nut
on the plunger bottom in or out. If the plunger sticks,
remove the solenoid from its mounting plate and
clean the plunger and recess in the solenoid.
1
PREHEATING CIRCUIT
This 12 volt battery circuit consists partly of manifold
heaters that heat the combustion air at the intake
manifold and a glow plug in each cylinder that heats
the precombustion chamber for engine starting,
Figure
17.
The manifold heater and glow plugs are
wired in parallel and are controlled by a preheat
switch on the control box.
GLOW
PLUG
.
MANIFOLD
HEATER
FIGURE
17.
GLOW PLUG AND MANIFOLD HEATER
Check each heater by removing its lead, operating
the preheat switch, and touching the lead to its
terminal.
If
it
sparks, there is continuity and the heater
is working. If any components of this circuit fail,
replace them.
Do
not attempt repairs on individual
components. If there is still a question, check the
component for heating.
FUEL
INJECTION PUMPS
The diesel is equipped with the model
PSU
fuel injec-
tion pumps.
The fuel injection pumps are constant stroke, lapped
plunger type and operated by the engine camshaft.
They deliver an accurately measured quantity of fuel
under high pressure to the injection nozzles.
A constant bleed check valve is furnished with all PSU pumps. The
bleed valve automatically bleeds off a restricted amount of fuel,
fuel vapors, and small quantities of air to prevent air accumulation
In the fuel sump area of the pumps. This valve should open at
pressures between
0.9
and
3.0
psi
(6.2
and
20.7
kPa).
INJECTION PUMP REPAIR
Internal repairs on the
PSU
injection pumps require
special tools and step-by-step procedures for dis-
assembly and reassembly.
Replace with new pumps injection
m
pumps that troubleshooting proce-
dures prove to be malfunctioning.
Do
not attempt
unauthorized repair procedures on the injection
pumps.
Refer to Diesel Starting Guide, page
9.
Fuel injection pumps must pass stringent quality
inspections and tests with precise settings and
adjustments in order to meet Onan’s performance
and reliability requirements. Therefore,
it
must be
clearly understood by the owners and by Onan ser-
vicemen that tampering or inept repair attempts can
cause irrepairable damage to the pumps that will not
be covered by the manufacturer’s warranties or
exchange agreements. Contact an authorized Amer-
ican Bosch Service station or Distributor for expert
repair service on the injection pumps.
The repair service should include cleaning, part
replacement, static pressure tests for internal and
external leaks, internal pump timing, and calibration
and adjustment to the manufacturer’s specifications.
CAUT,ON
PSU INJECTION PUMP
The PSU injection pump (Figure 18)
is
used on Onan
4-cylinder water-cooled diesels.
FIGURE
18.
PSU INJECTION PUMP
28
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