Wastegate Testing
How to perform a low-boost pressure test to determine if the boost problem is mechanical or electronic, and how to bench-test the wastegate diaphragm with a pressure pump to verify opening pressure and sealing.
Introduction
If the 944 Turbo is not achieving full boost, the first step is to determine whether the problem is in the electronic boost control system or in the mechanical components. The low boost pressure test below distinguishes between these possibilities.
Low Boost Pressure Test
- Clamp the wastegate actuating line using a hose clamp.
- Test drive the vehicle and note the maximum boost pressure.
Caution: Use extreme caution when driving with the actuating line clamped. Clamping the line defeats the overboost protection system. If the turbocharger and wastegate are mechanically sound, the engine can overboost and suffer serious damage.
- If boost reaches 1.75 bar on the car's boost gauge, the mechanical portion of the charging system (wastegate, turbocharger, air intake, turbo bypass valve) is functioning correctly. If 1.75 bar is not achieved, proceed to testing individual mechanical components.
Wastegate Testing
- Wastegate testing must be done with the exhaust system cold at the start of the test.
- Raise the vehicle on jack stands.
- Disconnect the wastegate actuating line and connect a hand pressure pump in its place.
- Start the engine and allow it to idle. The exhaust line to the wastegate will heat up. If the wastegate is closed and not leaking, the bypass line out of the wastegate will remain cold.
- Using the pressure pump, slowly apply pressure to the wastegate while feeling the bypass line with your hand.
Note: Do not apply more than approximately 14.5 psi (1 bar) to the wastegate diaphragm during testing. The factory shop manual specifies 0.6 bar (8.7 psi) to open the wastegate, but independently verified field measurements from multiple owners indicate different actual opening pressures — see the values below.
- At approximately 4 psi (0.28 bar), the wastegate should begin to open, indicated by the bypass line starting to warm up. At approximately 7 psi (0.48 bar), the wastegate should be fully open.
- When pressure is suddenly released, the wastegate should snap closed with an audible click.