CM870 and ISX Engines – 010-999   Air Intake System – Overview

The ISX with CM870 variable geometry turbocharger is pneumatically actuated with air from the OEM air tanks. High air pressure from the turbocharger control valve closes the variable geometry mechanism, which increases the exhaust gas pressure and facilitates EGR flow through the engine. A closing variable geometry mechanism also increases turbocharger speed and intake manifold pressure under certain engine operating conditions. Lower air pressure from the turbocharger control valve opens the variable geometry mechanism, which decreases exhaust gas pressure, turbocharger speed, and manifold pressure under certain engine operating conditions.

Depending on the build date, the ISX with CM870 uses either a low mount turbocharger control valve or a high mount turbocharger control valve.

The early ISX with CM870 use the high mount turbocharger control valve, which is located on top of the front gear housing.

The air filter is located on the air shut-off valve.

The later ISX with CM870 engines, engine serial number first (ESN) 79031440 uses the low mount turbocharger control valve. The low mount turbocharger control valve does not require an air filter.

However, the vehicle must be equipped with an air dryer to meet engine installation requirements. The vehicle air supply will be plumbed directly to the control valve inlet port (1). The outlet air supply port (2) to the variable geometry turbocharger .

The ISX with CM871 variable geometry turbocharger is electronically actuated. The electronic control module (ECM) sends a command directly to the variable geometry actuator mounted on the turbocharger.

Closing the variable geometry mechanism increases the exhaust gas pressure, facilitating EGR flow through the engine. Turbocharger speed and intake manifold pressure will also increase when the variable geometry mechanism closes under certain engine operating conditions. Closing the variable geometry turbocharger will also increase exhaust gas temperature under certain normal engine operating conditions and during aftertreatment regeneration events. This is used to improve aftertreatment component efficiency. Refer to Procedure 011-999 for further information regarding variable geometry turbocharger and aftertreatment system interactions.

Opening the variable geometry mechanism decreases exhaust gas pressure, turbocharger speed and intake manifold pressure under certain engine operating conditions.

The combustion air system consists of intake air piping, turbocharger, charge-air cooler piping, charge air cooler, and exhaust piping.

The turbocharger uses exhaust gas energy to turn the turbine wheel. The turbine wheel drives the compressor impeller that provides pressurized air to the engine for combustion. The additional air provided by the turbocharger allows more fuel to be injected to increase the power output from the engine.

The correct turbocharger must be used. Providing too much additional air will increase the cylinder pressures and shorten the life of the engine.

The turbine and compressor wheels and the shaft are supported by two rotating bearings in the bearing housing. Passages in the bearing housing direct filtered, pressurized engine oil to the shaft bearings and thrust bearings. The oil is used to lubricate and cool the rotating components to provide for smooth operation. The oil then drains from the bearing housing to the engine sump through the oil drain line.

An adequate supply of good, filtered oil is very important to the life of the turbocharger.

As the intake air is compressed by the turbocharger, the air temperature increases. This heated air is then passed through the charge-air cooler, which cools the air. Cool air is more dense, which allows more air to be compressed into the cylinder, yielding a much greater combustion efficiency.