Turbo-charged engines allow automotive designers the freedom to create vehicles that offer impressive power output ratios from more compact engines, enabling a reduction in weight and volume, as well as decreased fuel consumption, and cleaner exhaust gases. Lower engine noise also generally results from the achievement of a target power output at lower engine speeds.

In order to maximise the response times of the turbocharger, the size of the unit is kept deliberately small, by matching it to the lower end of the engine’s speed range. However, this strategy generates the problem of potential over-speed of the turbocharger’s rotor at higher engine speeds.

Independent wastegates were traditionally used but as packaging requirements have become more of an issue, wastegate valves are integrally incorporated into the turbine housing of the turbocharger and so a separate device is required to operate it. The actuator resolves this problem by forcing the waste-gate valve to open at a pre-set boost pressure, so allowing some engine exhaust gas to bypass the turbine and thus preventing over-speeding. As the engine speed decreases, the waste-gate valve is closed, and the actuator piston movement is completed.

In addition, by preventing excessive airflow into the engine, the emission of oxides of nitrogen pollutant into the atmosphere is reduced.

The traditional turbocharger actuator is a mechanical pneumatic device that senses boost pressure and opens the wastegate valve once a predetermined pressure is reached. The air pressure is sensed typically from either the inlet manifold or the compressor housing of the turbocharger. Inside the canister of the actuator the main components are a diaphragm, retaining cup and spring. The spring is designed to compress below the diaphragm. These two components are separated by the cup, attached to which is a rod that links to the pivoting wastegate.

Failures are extremely rare within the normal service life of the component but occasionally it can happen. The diaphragm can split and occasionally the rod or spring can fracture. The most common problem is the spring ‘going weak’ generally due to excessive heat and thus the wastegate is opened prematurely causing a drop in boost pressure. In service conditions the actuator’s opening pressure can be easily checked against original tolerance by using one of the pieces of workshop equipment we can provide.

Standard ‘genuine’ replacement actuators are available for most applications. See Spare Parts for further information.

When not available as a separate component Turbo Dynamics will usually have a solution for you using one of our large range of exclusively built units or by accessing our bespoke database of interchangeable items.

Turbo Dynamics also offers an exclusive range of up rated wastegate actuators to replace the standard item. These are constructed from the same quality components used by Garrett with the exception of the spring. The same high grade material and design techniques are used but the spring tensions are increased. This allows us to offer a huge range of opening pressures to suit high output applications.

Like turbochargers in general, the wastegate actuator is the most common component to get the blame incorrectly for a whole manner of engine problems. Remember it is only a pneumatic device that opens and shuts the wastegate. It’s calibration is very important but either it is or it isn’t working! Most of the actuators these days are controlled by an electronic solenoid which in turn gets it’s input from the ECU.

For this example, we are taking a petrol engined car that should run a boost pressure of 1 Bar (14.5 p.s.i.), is intercooled and utilises an electronic solenoid, controlled by the engine’s ECU to open the wastegate actuator.

If your boost pressure is down the first check that should be carried out is a boost pressure test, both at the inlet manifold and then at the compressor housing of the turbocharger. If there is a difference of more than 1 – 1.5 p.s.i. then the chances are that you have an air leak from the ducting from the turbo to the intercooler or from the intercooler to the plenum/inlet manifold or from the intercooler itself. If the pressure measured is about half what it should be the chances are that the solenoid is not working. To check this, route a new piece of pressure pipe from the compressor housing boost nipple (if fitted) directly to the wastegate actuator. This then by-passes the solenoid. Re-test. If you get the same results you know that the solenoid is not working. By doing this test, the turbocharger will produce whatever pressure the actuator is set to open at. Normally, on a car that utilises a solenoid control in the system, the actuator will be set to open at half the ‘normal running pressure’. For example, on this application the wastegate actuator will be calibrated to open at 0.5 Bar. The solenoid, when running at maximum duty cycle will bleed off enough air to allow the turbo to produce 1 Bar of pressure before the wastegate opens. Solenoids are used generally as a safety device. To give you one example, on a cold morning when you jump in the car, the ECU will not activate the solenoid until the engine is at normal running temperature. Until this temperature is reached the turbo will only be allowed to produce the pressure that the wastegate actuator is set to open at (0.5 Bar, 7.25 p.s.i.). Once at temperature, the solenoid is then operated by a frequency modulation from the ECU and bingo 1 Bar of boost pressure.

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