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Section 5
ENGINE DC CONTROL SYSTEM
INTRODUCTION
The engine DC control system includes all compo-
nents necessary for the operation of the engine.
Operation includes rest, priming, cranking, starting,
running and shutdown. The system is shown
schematically In Figure 5-1.
OPERATIONAL ANALYSIS
CIRCUIT CONDITION- REST:
Battery voltage is available to the engine controller
circuit board (PCB) from the unit BATTERY and via
(a) the RED battery cable, Wire 13, a 7.5 amp FUSE
(F1), Wire 15 and circuit board Terminal J3. However,
circuit board action is holding the circuit open and no
action can occur.
Battery output is available to the contacts of a
STARTER CONTACTOR (SC), but the contacts are
open.
Battery voltage is also delivered to the FUEL
PRIMER SWITCH (SW2). The switch is open and the
circuit is incomplete.
CIRCUIT CONDITION- PRIMING:
When the FUEL PRIMER SWITCH (SW2) is closed by
the operator, battery voltage is delivered across the
closed switch contacts and to the FUEL PUMP (FP)
via Wire 14A. The FUEL SOLENOID (FS) will be ener-
gized open via Wire 14 during cranking and running.
CIRCUIT CONDITION- CRANKING:
When the START-STOP SWITCH (SW1) is held at
"START" position, Wire 17 from the engine controller
circuit board is connected to frame ground. Circuit
board action will then deliver battery voltage to (a) a
STARTER CONTACTOR (SC) via Wire 56, and to an
automatic CHOKE SOLENOID (CS) via Wire 90.
When battery voltage energizes the STARTER CON-
TACTOR (SC), its contacts close and battery output
is delivered to the STARTER MOTOR (SM) via Wire
16. The STARTER MOTOR (SM) energizes and the
engine cranks. When the STARTER CONTACTOR
(SC) closes, battery voltage is delivered to the engine
controller board for field boost.
CIRCUIT CONDITION-CRANKING:
While cranking, the CHOKE SOLENOID (CS) is ener-
gized cyclically by circuit board action (two seconds
on, two seconds off).
Also while cranking, circuit board action delivers bat-
tery voltage to the Wire 14/14A circuit. This energizes
the FUEL PUMP (FP) ,FUEL SOLENOID (FS) and
CHOKE HEATER (CH).
Circuit board action holds open Wire 18A to common
ground. The Magneto will induce a spark during cranking.
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CIRCUIT CONDITION-RUNNING:
With the FUEL PUMP (FP) operating and Ignition
occurring, the engine should start.
A voltage is induced into the Stator's BATTERY
CHARGE WINDING. This voltage is delivered to the
ENGINE CONTROLLER BOARD (PCB) via Wire 66
to prevent STARTER MOTOR engagement above a
certain rpm.
Circuit board action terminates DC output to the
STARTER CONTACTOR, which then de-energizes to
end cranking and CHOKE SOLENOID operation. The
choke will go to a position determined by the CHOKE
HEATER (CH).
CIRCUIT CONDITION- SHUTDOWN:
Setting the START-STOP SWITCH (SW1) to its
"STOP" position connects the Wire 18 circuit to frame
ground. Circuit board action then closes the circuit to
Wire 18A, grounding the ignition coil. Circuit board
action opens the circuit to Wire 14. Ignition and fuel
flow terminate and the engine shuts down.
CIRCUIT CONDITION- FAULT SHUTDOWN:
The engine mounts a HIGH OIL TEMPERATURE
SWITCH (HTO) and a LOW OIL PRESSURE
SWITCH (LOP).
Should engine oil temperature exceed a pre-set
value, the switch contacts will close. Wire 85 from the
circuit board will connect to frame ground. Circuit
board action will then initiate a shutdown.
Should engine oil pressure drop below a safe pre-set
value, the switch contacts will close. On contact clo-
sure, Wire 85 will be connected to frame ground and
circuit board action will initiate an engine shutdown.
The circuit board has a time delay built into it for the
Wire 85 fault shutdowns. At STARTUP ONLY the cir-
cuit board will wait approximately 6 seconds before
looking at the Wire 85 fault shutdowns. Once running
after the 6 second time delay, grounding Wire 85 thru
either switch will cause an immediate shutdown.
ENGINE CONTROLLER CIRCUIT BOARD
GENERAL:
The engine controller board is responsible for crank-
ing, startup, running and shutdown operations. The
board interconnects with other components of the DC
control system to turn them on and off at the proper
times. It is powered by fused 12 VDC power from the
unit battery.
CIRCUIT BOARD CONNECTIONS:
The circuit board mounts a 15-pin receptacle (J1) and
two single pin terminals (J2 and J3, see Figure 5.2).
Figure 5-3 shows the 15-pin receptacle (J1), the asso-
ciated wires and the function(s) of each pin and wire.
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Troubleshooting
