Ford Workshop Service and Repair Manuals

Principles of Operation - Vehicles with fixed vane turbocharger

The turbocharger is governed by a wastegate control valve. The wastegate control valve redirects some of the exhaust gas past the turbine and therefore acts as a governor. The wastegate control valve is preset during manufacture and must not be tampered with.

Principles of Operation - Vehicles with variable vane turbocharger

The turbocharger is designed to improve engine induction and engine performance. The list below details the concerns relating to turbocharger performance.

• High engine speed produces excessive turbine speed and therefore creates excessive turbocharger boost pressure.
• Low engine speed does not produce sufficient turbine speed and therefore not enough turbocharger boost pressure is achieved.

The variable vane turbocharger does not have a wastegate control valve. Instead, it has variable turbocharger vanes which are located in the turbocharger turbine housing. The turbocharger vanes act as the control for the turbocharger boost pressure.

The variable 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 velocity of the exhaust gas.

The speed of flow of the stream of exhaust gas is increased independent of engine speed by varying the intake cross section in front of the turbocharger turbine.

The variable vanes are controlled by the PCM. A duty cycle signal from the powertrain control module (PCM), controls a vacuum supply to the turbocharger vacuum diaphragm unit using a solenoid valve.

Regulation at Low Engine Speed

At low engine speeds the PCM actuates the vane adjustment solenoid valve to enable a vacuum to be applied. The vacuum diaphragm unit moves the adjusting ring so that the vanes are set at a shallow angle. The reduced intake cross section this creates for the stream of exhaust gas increases the exhaust gas velocity allowing 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 as a result, the vane adjustment solenoid valve adjusts the vacuum level within the vacuum diaphragm unit. The vacuum diaphragm unit 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 e.g. in the event of an electrical concern or leak in the vacuum system. Therefore, there is little chance of engine damage due to excessive boost in the event of a turbocharger control concern.

Inspection and Verification

NOTE:The turbocharger uses engine oil as a lubricant. Due to the high operating temperatures of the turbocharger and the expansion and contraction of the internal components a proportion of engine oil may enter the air intake system. This is not an indication that the turbocharger oil seal has failed.

NOTE:The turbocharger oil seal will not fail unless the bearings fail first, which will cause the turbocharger to become very noisey. Do not install a new turbocharger due to oil inside the turbocharger or the air intake components. If a leak is detected in the supply or return tubes or connections, locate and rectify the source. Do not install a new turbocharger due to an oil leak.

Visual Inspection Chart

Symptom Chart

NOTE:On vehicles with variable vane turbocharger the vacuum diaphragm unit and actuator rod are fixed parts of the turbocharger and cannot be adjusted or renewed.

Symptom Chart

Pinpoint Tests