G3500B Engines Caterpillar

The Electronic Control Module (ECM) provides control of the air/fuel mixture to the engine. Illustration 1 is a diagram of the fuel system's main components. The flow of fuel through the system is explained below.

Illustration 1	g00999022

The fuel flows from the main gas supply through the fuel filter. Usually, the fuel filter is a component of the design at the particular site. The customer is responsible for supplying clean, dry fuel to the engine. The fuel filter may be supplied by Caterpillar or by the customer. To prevent particles from entering the engine, a one micron filter is recommended. The filter must be properly sized for the required gas pressure.

For installation of the fuel filter, the recommended location is close to the engine before the engine's gas pressure regulator. Pressure gauges in the gas lines on each side of the fuel filter are recommended in order to monitor the filter's differential pressure. A manual shutoff valve in the gas line before the fuel filter will facilitate servicing of the filter.

The filtered fuel flows to the Gas Shutoff Valve (GSOV). The GSOV may be supplied by Caterpillar or by the customer.

The control system is configured for a GSOV that is energize-to-run. This means that the GSOV must be energized in order for the engine to run. To enable the fuel flow, the ECM provides +Battery voltage to the solenoid for the GSOV. The valve opens and the fuel flows to the engine. When the control system shuts down the engine, the voltage is removed from the solenoid. The valve closes and the fuel is shut off.

The fuel flows through the GSOV to the gas pressure regulator. The regulator may be supplied by Caterpillar or by the customer. A regulated pressure of 7 to 35 kPa (1 to 5 psi) is recommended. Less pressure may result in reduced power. More pressure may result in instability.

The engine can operate with a minimum fuel pressure of 7 kPa (1 psi). Fluctuations of the fuel pressure prior to the fuel control valve will have a negative effect on the stability of the engine rpm. Control of emissions can also be affected. Ensure that the fuel pressure is stable within ± 0.25 kPa (± 0.04 psi).

The regulated fuel flows to the electronically controlled fuel metering valve. The ECM issues a command signal to the fuel metering valve. The fuel metering valve regulates the flow of fuel to the engine.

The fuel metering valve controls the volume of fuel that flows to the turbocharger compressor. The inlet air that is necessary for combustion also enters the turbocharger compressor. The air and fuel are mixed.

The compressed air/fuel mixture flows to the aftercooler. The temperature of the compressed air/fuel mixture is reduced in the aftercooler. This increases the density of the air/fuel mixture. This results in more efficient combustion.

The cooled air/fuel mixture flows to the electronically controlled throttle. The ECM issues a command signal to the throttle's actuator. The signal is based on the desired engine speed. The throttle controls the volume of the air/fuel mixture that flows to the air inlet manifold.

The air/fuel mixture flows from the throttle through the air inlet manifold. The manifold distributes the air/fuel mixture to the cylinders for combustion.