The main components of the APV system are the following.
A. Lighting Coil
B. Chassis Control Unit (CCU)
C. ECU
D. Servomotor
E. Power Valve Cables
F. Power Valves
Lighting Coil
The AC current generated by the lighting coil, which
flows to the CCU, is the power source for the APV
system.
Chassis Control Unit (CCU)
The AC current from the lighting coil first enters the
CCU which is then changed from AC current to DC
current. Since the APV circuit cannot use pulsating
DC current, it must be converted (by the CCU) to
straight DC current which is necessary for the APV
system.
ECU
The computer within the ECU has been programmed
to raise and lower the power valves at a specific engine
rpm. When this rpm is reached, DC current is routed to
the servomotor by the ECU.
Servomotor
The servomotor consists of two circuits. One circuit is
a DC circuit, which operates the DC motor within the
servo, and the other is a potentiometer, which measures
the servo pulley position based on voltage.
The computer within the ECU has been programmed
to operate the servomotor between a low and high
voltage range. If voltage is not within the range, the
computer will shut down the APV circuit. The computer
will then make a total of three more attempts to
cycle the power valves. If the correct voltage or pulley
position isn’t seen, the APV circuit is shut down and
no more attempts will be made until the engine is shut
down and restarted.
Cables
The exhaust valves are connected to the actuating
cables and, along with the return springs, are contained
inside the APV housing on the exhaust side of each
cylinder. The other end of the actuating cable is connected
to the servo.
OPERATION
At idle and low speed operation, the exhaust valves are
held in the “low port” position by the return spring.
When engine RPM reaches a predetermined point, the
ECU will send a signal to the servo which will cycle
and pull the exhaust valves into the up or “high port”
position. The RPM at which the valves open is different
with each model.
If the servomotor cycles the exhaust valves as
explained above, the exhaust valve circuit is operating
satisfactorily. If the servomotor makes no attempt to
open the valves or if the servo attempts to cycle the
valves three times (then stops working), there is a
problem and it must be corrected.
Servomotor Cycles Three Times
In this situation the ECU computer has been programmed
with a voltage range (low and high) that the
servomotor must operate within. If the servomotor is
put under too much load, its resistance goes up and
may exceed the range upper limit. It will then stop and
attempt two more times. If the resistance still is too
high, it shuts down.
If the servo is commanded to move but the potentiometer
output voltage does not change, an error occurs
and the check engine light will flash a trouble code.
Improper servomotor position sensing is normally
caused by one or more of the following:
A. Incorrect exhaust valve cable length (too long
or too short).
B. Exhaust valve cable(s) sticking, broken, or disconnected
at pulley.
C. Exhaust valves sticking.
D. Exhaust valve spring(s) weak or broken.
Check each of the above probable causes in the order
given to locate the problem of the servomotor cycling
three times in succession; then shutting down.
Check for correct exhaust valve cable length specifications
for model being worked on in this section.
Servomotor Makes No Attempt To
Cycle
If when running the engine the servomotor makes no
attempt to operate, this is caused by one or more of the
following:
A. Bad connection from the wiring harness and
connector from the lighting coil to the CCU, to
the ECU, or from the ECU to servomotor.
B. CCU output (gauge/taillight/APV) is shorted or
open.
C. ECU output to servomotor is too low.
D. Servomotor failure
TROUBLESHOOTING
The APV system has a self-testing mode built in.
Every time that the engine is started, the servo will
cycle once. The ECU monitors the voltages at the
servo during this cycle to assure they are within operational
tolerances.
If all voltages are within tolerance, the system is ready
for operation. If the voltages are not within tolerance,
the servo will cycle two more times. If the voltages
remain out of tolerance, the system will not operate.
For example, if the headlight and taillight are disabled,
the ECU will sense a high voltage condition and activate
the fail-safe mode. Adding more than 4 amps of
accessories will create a low voltage condition and
activate the fail-safe mode.
The fail-safe mode is an ECU operated engine RPM
limiter. When activated, the fail-safe mode will be
seen as an immediate loss of engine horsepower.
! CAUTION
On the 600 cc, the long side of the exhaust valve
must be facing toward the cylinder head or severe
engine damage may occur.
600 cc
800/1000 cc
Problem: Engine loses power; no top end
Condition Remedy
1. Exhaust valves sticking
in down position
1. Remove carbon deposits,
burrs, etc.
2. Cables adjusted too
long
2. Inspect—adjust
3. CCU output voltage out
of tolerance
3. Inspect—replace CCU/
stator
Problem: Poor acceleration; hesitation
Condition Remedy
1. Exhaust valve sticking
in up position
1. Remove carbon deposits,
burrs, etc.—inspect/
replace return spring
2. Cables adjusted too
short
2. Inspect—adjust
3. CCU output voltage out
of tolerance
3. Inspect—replace CCU/
stator
Servomotor Test
��NOTE: A 12-volt battery and test leads will be
needed for this test.
1. Remove the servomotor from the snowmobile
2. Contact the red/black servo terminal with the battery
positive lead; then contact the black/red servo
terminal with the battery negative lead.
3. The servo should rotate when the negative lead
contacts the black/red terminal. Note the direction
of rotation.
4. Reverse the connections on the servo terminals:
positive lead to black/red and negative lead to red/
black. The servomotor should rotate in the opposite
direction.
5. Install the servomotor.
��NOTE: If the servo operates correctly in the
above test but fails to operate when connected to
the ECU/CDI at the designated RPM, proceed to
Potentiometer Test.
Potentiometer Test
��NOTE: The following test should be made using
MaxiClips (p/n 0744-041) and the Fluke Model 73
Multimeter (p/n 0644-191) set to the ohms scale.
1. Remove the servomotor from the snowmobile.
2. Connect the red maxiclip and meter lead to the
black/white servo terminal; then connect the black
maxiclip and meter lead to the yellow servo terminal.
3. Rotate the servo pulley counterclockwise. The
ohms should increase as the pulley is rotated until
it reaches 4700-5000 ohms.
4. Continue the pulley rotation, and there will be a
small area in the rotation at which the ohm reading
will disappear; then it will return again.
5. Continue the pulley rotation, and the ohms should
appear at a very low value but will again increase
to 4700 ohms. This is normal operation.
6. Install the servomotor.
��NOTE: If the servo operates correctly and the
potentiometer test is correct but fails to operate
when connected to the ECU/CDI at the designated
RPM, replace the ECU/CDI.
