Saturday, December 25, 2010

The 1991-94 Mercury Capri XR2 Turbo Engine FYI

Basic Operational FYI

The 1991-94 mercury Capri XR2 turbo engine produces 132 hp compared to the same engine without a turbo producing only 115 hp. When maintained, it is not uncommon for no serious issues to develop well past 100,000 miles. Owning the XR2 model is the way to go because owning an automatic produces an underpowered car-a dog from a standstill. The automatic only has 100 hp. The 5 spd non-turbo produces 115 hp and provides enough zip-barely. The XR2, when accelerating, pushes you into the seats-it is quick and agile.

Most are new to this car, so its nuances are not well known, only 66,000 were made and even less XR2 models. Part of the problem with any car is knowing where things are. Unless you are accelerating in the XR2, the boost gauge will remain flat. It will remain so if the speed is steady.

The turbocharger systom improves the engine power output by compressing the inlet air to a denser charge. Up to approximately 60 percent increase above the atmospheric pressure is attainable. It utilizes some of the energy in the hot exhaust gas to turn the turbine which drives the air compressor. The turbine and the air compressor comprise the turbocharger assembly, together with the exhaust bypass device, or the wastegate.

Since considerable heat is added to the air during compression, the air is cooled by routing it through a heat exchanger, the Charge Air Cooler (CAC). This reduces the possibility of preignition and engine damage from overheating. From the charge air cooler, the cooler air is ducted through the Volume Air Flow (VAF) meter to the engine intake manifold.

Boost Pressure Control

The boost pressure control system consists of a wastegate valve and a wastegate actuator. The actuator, which is controlled by turbo boost pressure, controls the wastegate valve, which opens and closes the exhaust gas bypass passage.

The amount of turbocharger boost is limited to a maximum of 56 kPa (8.1 psi) by the wastegate and actuator. Under normal to moderate loads, the wastegate valve is closed and the intake air pressure changes in accordance with the engine rpm and the amount of exhaust gas. Under heavy loads, the intake air pressure in the air inlet duct reaches 56 kPa (8.1 psi), the pressure acts on the diaphragm and overcomes the force of the spring within the actuator, and the wastegate valve opens the bypass passage. As a result, the flow of exhaust gas applied to the turbine wheel drops, the rpm of the turbine wheel drops, and the boost pressure drops accordingly.

Overboost Protection

If the actual intake manifold pressure reaches 77 kPa (1 1 psi) and the calculated intake manifold pressure (calculated from the amount of intake air and engine speed) reaches a predetermined level, the fuel injection will be cut to prevent engine damage. Under this condition the turbo boost gauge will be indicating in the red sector of the gauge.

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