Polaris msx 110 Service Manual page 157

FUEL INJECTION / IGNITION / EXHAUST SYSTEMS
Turbocharger
WARNING!
The turbocharger generates excessive heat and houses rotating parts which can cause severe injury and
burns. Never touch any part of the turbocharger assembly while the engine is running. Allow the engine
to completely cool before working with any component. Do not allow objects such as clothing, hair or
fingers to come into contact with, or enter the compressor impeller while the engine is running.
The turbocharger uses the energy of expanding exhaust gases to power a compressor. Intake air is drawn into
the compressor impeller and pre--compressed before entering the combustion chamber.
Components of the turbocharger employed on the MSX 110 and 150 watercraft are:
Turbine
S
Compressor (Impeller)
S
Bearing House
S
Wastegate Solenoid
S
Wastegate Actuator
S
The turbine is directly exposed to exiting exhaust gases. The exhaust gases from each cylinder increase in speed
as engine RPM increases and expand inside of the turbine housing. These gases are forced around the turbine
housing and out into the exhaust pipe, thus rotating the turbine.
A compressor impeller is connected to the turbine via a shaft. The shaft's bearings are lubricated with engine
oil and the bearing house is cooled by engine coolant. The compressor impeller draws fresh air into the compres-
sor housing. The fresh air is compressed, then routed on to the intake system. At WOT, the turbine / impeller
shaft can reach speeds in excess of 130,000 RPM.
The turbocharger bearing house is lubricated by the engine oil circuit and cooled by the engine coolant circuit.
The exhaust manifold and turbine housing are cooled by the freshwater cooling circuit. A loss or failure in any
one of the circuits will cause severe turbocharger and engine damage.
Wastegate
The amount of pre--compressed intake air generated by the compressor impeller is called boost pressure. Intake
boost pressure rises and falls in direct relation to turbine / impeller speed. Excessive boost pressure is a destruc-
tive force and therefore is constantly monitored and adjusted by the ECU.
The wastegate solenoid and wastegate actuator are two critical components responsible for allowing the ECU
to control boost pressure.
During operation, a small amount of pre--compressed air is routed to the wastegate solenoid. The wastegate
solenoid is electronically controlled by the ECU. Once opened by the ECU, the wastegate solenoid routes pre--
compressed air to the wastegate actuator.
The wastegate actuator houses a belows, spring, and actuator arm. The actuator arm is connected to a small
door located inside of the turbine housing. The actuator arm is held in the closed position by the spring. The
belows is exposed to boost pressure whenever the wastegate solenoid is opened. The actuator arm is pushed
open when the boost pressure acting upon the belows overcomes the spring pre--load. This action opens the
small door inside the turbine housing allowing the exhaust gases to bypass the turbine blades.
Allowing the exhaust gasses to bypass the turbine blades decreases the turbine / impeller shaft RPM, and lowers
boost pressure.
5.32
2004 Four Stroke PWC Service Manual