Polaris Virage TX 2000 Service Manual page 281

FFI™ FUEL INJECTION
Theory
External EMM Sensors
Air Temperature Sensor: The air temperature sensor monitors the temperature of air entering the air silencer.
The AT sensor is a Positive Temperature Coefficient (PTC) thermistor, a resistor whose resistance changes with
temperature and alters voltage values accordingly. When temperature increases, both resistance and voltage
also increase. When temperature decreases, resistance and voltage likewise decrease.
Water Temperature Sensor: The water temperature sensor is located in the exhaust manifold. It is held in a
seat in the water passage of the manifold, but does not actually contact the water. The sensor has a dual purpose;
it provides data to the EMM primarily for use in adjusting the air/fuel ratio during engine warm-up, and it sends
a signal to the EMM that will trigger the MFI "check engine" light in the event of an engine overheat.
The water temperature sensor is also a Positive Temperature Coefficient (PTC) thermistor, a resistor whose re
sistance changes with temperature. When temperature increases, both resistance and voltage also increase.
When temperature decreases, resistance and voltage likewise decrease.
If sensor values are above the limits (engine overheat), the EMM will initiate S.L.O.W. ™, store a service code,
and turn on the MFI "check engine" light.
If sensor values are below the limits, or the sensor or its circuit malfunctions, the EMM will store a service code,
and turn on the MFrcheck engine" light. The engine will not go into S.L.O.W.™.
Throttle Position Sensor: The Throttle Position Sensor (TPS) is a rotary potentiometer. It's located on the rear
of the throttle bodies by the EMM.
The sensor receives a voltage signal from the EMM. As the throttle lever is rotated, the EMM receives a return
voltage signal through a second wire. This signal is relative to the position of the throttle. As the throttle opens,
voltage increases. As the throttle closes, voltage decreases. A third wire completes the ground circuit back to
the EMM.
If sensed values are out of limits, or the sensor or its circuit fails, the EMM will turn on the "check engine" light
and store a service code. If the TPS becomes open during engine operation, engine RPM will drop to idle speed.
The engine will not accelerate above idle until the fault is corrected and the EMM is powered down by removing
the lanyard. Wait ten seconds and power up the system by inserting the lanyard.
When replacing a TPS sensor, calibration must be performed. Using Polaris Diagnostic Software, PN2873377,
enter "Service Utilities / Engine Monitoring" screen. Under "sensors" chart, look for 'TPS CAL" With the throttle
lever wide open, the calibration should read 78-80% open. If TPS is out of this range, loosen throttle cable at
throttle bodies and tighten or loosen cable as needed to achieve 78-80% open.
Crankshaft Position Sensor: The Crankshaft Position Sensor is a magnetic device. It generates a magnetic
field that's induced by the flywheel encoder ribs passing by it. This produces an AC voltage signal directly related
to flywheel RPM. Crankshaft TDC is determined by encoder rib spacing.
The sensor feeds the flywheel encoder data to the EMM, which calculates crank position and engine speed. The
EMM generates a tachometer signal, and controls fuel injector and ignition operation. The sensor is located on
the top of the flywheel housing on the MAG side of the engine.
If the Crankshaft Position Sensor or its circuit fails, the engine will not run. A sensor that is damaged or
out of adjustment will NOT turn on the "check engine" light but will store a service code only if the failure occurs
while the engine is running.
NOTE: Crankshaft sensor operation can be verified by the Engine Monitoring screen of the Polaris Diagnostic
Program. RPM on the screen should reflect engine RPM while cranking.
3/00 8.4 Polaris Sales Inc.