Throttle Position
Sensor
(EFI Models)
NOTE: Ignition timing specifications are located
on the Electrical Specifications Chart in this section.
TESTING TPS
When checking ignition timing, it is important that the
timing light be connected to the number 1 spark plug
wire, which is the MAG-side cylinder. If the number 2
cylinder spark plug wire is used, the timing light may
show a 2° error in ignition timing when ignition timing
is actually correct.
For example, the correct ignition timing on the 500 cc
is 12° ± 2° BTDC at 2000 RPM.
To quickly check TPS operation, measure the timing
according to the chart; then disconnect the TPS wiring
and recheck the timing. A system with a functioning
TPS will show a change in the timing. This is known
as “Fail-Safe Ignition Timing” and is built into the system
to protect the engine should the TPS fail. If this
change is not seen, the TPS may have failed and must
be checked
If the ignition timing isn’t 12° ± 2° at 2000 RPM, the
TPS should be checked for proper adjustment using
the Throttle Position Sensor Adjustment Tool Kit (p/n
3639-891) and a digital voltmeter.
VERIFYING TPS ADJUSTMENT
TOOL
Before using the TPS adjustment tool, verify its battery
condition. The battery used in the tool is a 9-volt
battery. To check battery condition, use a digital volt/
ohmmeter set on DC volt scale. Test between the
adjustment tool black and red jacks. Insert the red lead
of the digital voltmeter into the red jack of the adjustment
tool and the black lead of the digital voltmeter
into the black jack of the adjustment tool. The green
power light of the analyzer should now be illuminated.
If voltage is found below 4.9 volts, replace the battery.
NOTE: The battery used in the tool is a 9-volt battery;
also, the Test Harness (p/n 0686-999) must be
plugged into the analyzer for testing voltage.
CHECKING TPS
NOTE: If the snowmobile is in warranty, breaking
the seal on the idle screw jam nut or the Phillipshead
screws on the TPS will void warranty. If the
TPS is tested out of specification, the throttle
assembly must be replaced.
NOTE: Before using the TPS adjustment tool,
verify its battery condition.
1. Using Throttle Position Sensor (TPS) Adjustment
Tool Kit (p/n 3639-891), connect its wiring harness
to the TPS. Connect the red and black digital
voltmeter leads to the white and black jacks of the
TPS adjustment tool.
2. Ensure that the throttle cable/control rod has the
proper amount of free-play.
3. With the throttle in the idle position, compare the
reading on the voltmeter to the chart. If the reading
is within prescribed specification, proceed to step 4
Engine Idle Position Wide-Open Position
500 cc 0.714-0.814 3.507-4.014
600/800 cc 0.646-0.754V 3.472-4.0485V
1000 cc 0.595-0.695V 3.477-4.054V
4. Compress the throttle lever slowly to the full-open
position. The meter reading should show a smooth
rise in voltage all the way to the full-open throttle
position. If the voltage seems to be erratic or
doesn’t meet the prescribed specification, repeat
this procedure several times to confirm results.
5. If the full-open throttle voltage remains erratic or
out of specification; replace the throttle body
assembly.
6. If the TPS is within the prescribed specification,
disconnect the adjustment tool harness from the
TPS. Connect the snowmobile TPS harness to the
TPS.
NOTE: Before installing the TPS harness connector,
apply dielectric grease to the connector pins.
FAIL-SAFE IGNITION TIMING
Engines equipped with throttle position sensor have a
protective feature called “fail-safe” ignition timing
which prevents engine damage should the TPS fail. If
the TPS does fail, the engine will run normally at low
RPM but will run poorly at high RPM. This will allow
the operator to get the snowmobile to safety with little
or no engine damage.
NOTE: The engine will continue to operate this
way until the TPS is replaced.
