Ford Transit 2002 Owner's Manual page 998

The turbocharger produces its full turbocharger boost pressure over the entire engine speed
range, not just at high engine speed. This is achieved through the adjustment of the vanes
and the resulting change in the flow of the exhaust gas.
The speed of the exhaust gas flow within the turbocharger is increased independent of
engine speed by varying the intake cross section in front of the turbocharger turbine. This
is achieved by adjusting the angle of the vanes controlling the exhaust gas flow into the
turbocharger turbine and this drives the turbocharger turbine faster. The higher
turbocharger speed produces a high turbocharger boost pressure at all engine speeds.
The powertrain control module (PCM) controls the turbocharger vanes by means of an
electronic vane adjustment solenoid attached to the turbocharger.
Regulation at Low Engine Speed
At low engine speeds the PCM operates the vane adjustment solenoid. The vane adjustment
solenoid moves the adjusting ring so that the vanes are set at a shallow angle. The shallow
intake cross section this creates for the stream of exhaust gas allows the turbocharger
boost pressure to build up rapidly and easily at low engine speeds.
Regulation at Moderate Engine Speed
As the engine speed increases and the quantity of exhaust gas increases, the vane
adjustment solenoid moves the adjusting ring so that the vanes are set at a steeper angle.
The steeper angle opens the intake cross section effectively reducing the gas flow and
turbine speed, while maintaining constant turbocharger boost pressure.
Regulation at Maximum Engine Speed
As the engine speed increases the intake cross section in front of the turbocharger turbine
is continuously enlarged. The turbine speed and hence the quantity of the air supplied to
the engine, is adjusted to suit the engine speed. This means that the turbocharger boost
pressure remains optimized over all engine speeds.
The maximum position of the turbocharger vanes (maximum opening cross section) is also
an emergency position, in the event of an electrical concern. This lowers the chance of
engine damage due to excessive boost in the event of a turbocharger control concern.
Fixed Vane Turbocharger
Item Part Number Description
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