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, screw the hex head cap
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.
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
18).
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
18.
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 componentsof this circuit fail, replace
them.
Do
not attempt repairs on individual com-
ponents. If there is still a question, check the compo-
nent for heating.
FUEL
INJECTION PUMPS
Onan diesels are equipped with the model
PSU
fuel
injection 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 bleedsoff 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
Wa).
INJECTION PUMP REPAIR
Internal repairs on the
PSU
injection pumps require
special tools and step-by-step procedures for dis-
assembly and reassembly.
Replace injection pumps that
troubleshooting procedures prove to be
malfunctioning with new pumps. Do not attempt unauthorized
repair procedures on the injection pumps.
Fuel injection pumps must pass stringent quality
inspections and tests with precise settings and ad-
justments in order to meet Onan’s performance and
reliability requirements. Therefore, it must be clearly
understood by the owners and by Onan servicemen
that tampering or inept repair attempts can cause
irrepairable damage to the pumps that will not be
covered by the manufacturers warranties or ex-
change agreements. Contact an authorized American
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.
PSU INJECTION PUMP
The
PSU
injection pump (Figure
19)
is used on Onan
2-cylinder water-cooled diesels.
FIGURE
19.
PSU INJECTION PUMP
22
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