The turbocharger senses boost pressure which actuates the wastegate valve which will control the amount of exhaust gas that will be allowed to bypass the turbine side of the turbocharger. The speed of the turbocharger is controlled by the wastegate valve.
(1) Actuating rod. (2) Canister. (3) Line.
When the engine is operating under low boost (lug) conditions a spring pushes against a diaphragm in canister (2) and moves actuating rod (1) to close the wastegate valve which will allow the turbocharger to operate at maximum performance.
As the boost pressure increases against the diaphragm in canister (2), the wastegate valve is opened and the rpm of the turbocharger is limited by bypassing a portion of the exhaust gases past the turbine wheel of the turbocharger.
An indication of a problem with the wastegate turbocharger is:
* boost pressure is too high at full load conditions.
* boost pressure is too low at all lug conditions.
The correct pressure for the inlet manifold is given in TMI (Technical Marketing Information).
To check the operation of the wastegate valve, verify the correct Wastegate Check Pressure by referencing the letter code stamped on the wastegate lever arm to the corresponding pressure. Remove the air line and slowly apply the check pressure to the canister. DO NOT EXCEED 200 kPa (29 psi).
The actuating lever should move 0.50 ± 0.25 mm (0.020 ±0.010 in) when the external supply of air connected to the line reaches the corresponding wastegate check pressure. If the actuating lever does not move 0.50 mm (0.020 in) replace the turbine housing assembly (which includes the wastegate) or the complete turbocharger.
To check the operation of the wastegate valve, remove line (3) and slowly apply 200 kPa (29 psi) of air to canister (2). DO NOT EXCEED 200 kPa (29 psi). The actuating lever should move more than .50 mm (.020 in) when the external supply of air is connected to line (3). If the actuating lever does not move at least .50 mm (.020 in), replace the turbine housing assembly (includes wastegate), or the complete turbocharger.
NOTE: The wastegate turbine housing assembly is preset at the factory and no adjustments can be made.
Maximum rpm of the turbocharger is controlled by the boost pressure (which controls the position of the wastegate valve), the engine rating, the high idle rpm setting and the height above sea level at which the engine is operated