Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Turbocharger

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A turbocharger is an exhaust-driven turbine which drives a compressor wheel on the other end of the same shaft. The turbine is located in the exhaust flow, generally just below the exhaust manifold. The compressor is located in the intake air path, usually between the air cleaner and the intake manifold. Even though the exhaust and intake air channels are connected by the turbocharger shaft, the exhaust is kept separate from the intake air at all times. (Think of the old water wheel turning the grinding wheel at the mill; the force is transferred but the water never touches the grain.)

By compressing the intake air, more air is squeezed into the cylinder carrying more oxygen for better combustion. Since more air is introduced, more fuel can be introduced, yielding more power. Turbocharging is one way of coaxing more power out of relatively small engines. A larger engine with the same power output would add additional weight, thus reducing overall performance. A turbocharger system is relatively light in comparison, and the additional weight of strengthened components is still well below the weight of a larger motor.

It is possible to get too much of a good thing. Turbocharging is self-perpetuating; that is, as boost (air compression) builds, the exhaust volume builds and the turbine turns faster, providing more boost and so on. If left alone, the turbocharger would build pressure well beyond the operating ability of the engine. To prevent these costly and spectacular failures, boost is held to a reasonable level by a wastegate. Usually located in the output elbow area, the wastegate is a pressure valve which activates at a pre-determined level of pressure. When it opens, it simply allows exhaust flow to bypass the turbine, thus limiting its speed. NEVER attempt to change the setting of the wastegate. If the wastegate or actuator is suspected of faulty operation, replace it.

As the intake air is compressed in the turbocharger, it becomes heated and expands. This expanding air flow is less dense so less air is forced into the engine, partially defeating the purpose of the turbocharger. To overcome this condition, some engines are fitted with an intercooler to remove heat from the air charge. A properly designed intercooler system can reduce air temperature by 90°F (32°C) or more. The intercooler is simply a heat exchanger located between the turbocharger and the intake manifold.

The compressed air charge is directed through ductwork to the intercooler where it is cooled and then on to the intake manifold. The system works in the same fashion as the radiator for the cooling system except that air is being cooled instead of fluid. In some cases the intercooler even looks like a small radiator. The cooled air charge once again becomes dense, introducing more air into the engine and providing more power, greater eco