Fuel Delivery System

FUEL DELIVERY SYSTEM
The fuel system on the Cummins 24 valve Turbo-Diesel Engine uses an electronic fuel injection pump with three control modules.

Also refer to the Powertrain Control Module (PCM) or Engine Control Module (ECM).

Fuel System Components:

Some fuel system components are shown.

The fuel delivery system consists of the:
- Accelerator pedal
- Air cleaner housing/element
- Fuel drain manifold (passage)
- Fuel filter/water separator
- Fuel heater
- Fuel heater relay
- Fuel transfer (lift) pump
- Fuel injection pump
- Fuel injectors
- Fuel heater temperature sensor
- Fuel tank
- Fuel tank filler/vent tube assembly
- Fuel tank filler tube cap
- Fuel tank module containing the rollover valve, fuel gauge sending unit (fuel level sensor) and a separate fuel filter located at bottom of tank module
- Fuel tubes/lines/hoses
- High-pressure fuel injector lines
- In-tank fuel filter (at bottom of fuel tank module)
- Low-pressure fuel supply lines Low-pressure fuel return line
- Overflow valve
- Quick-connect fittings Throttle cable
- Water draining

FUEL TANK MODULE
An electric fuel pump is not used in the fuel tank module for diesel powered engines. Fuel is supplied by the engine mounted fuel transfer pump and the fuel injection pump.

Top View Of Fuel Tank Module:

The fuel tank module is installed in the top of the fuel tank. The fuel tank module contains the following components:
- Fuel reservoir
- A separate in-tank fuel filter
- Rollover valve
- Fuel gauge sending unit (fuel level sensor)
- Fuel supply line connection
- Fuel return line connection
- Auxiliary non-pressurized fuel supply fitting

FUEL GAUGE SENDING UNIT
The fuel gauge sending unit (fuel level sensor) is attached to the side of the fuel tank module. The sending unit consists of a float, an arm, and a variable resistor (track). The resistor track is used to send electrical signals to the Powertrain Control Module (PCM) for fuel gauge operation. After this signal is sent to the PCM, the PCM will transmit the data across the CCD bus circuits to the instrument panel. Here it is translated into the appropriate fuel gauge level reading.

As fuel level increases, the float and arm move up. This decreases the sending unit resistance, causing the fuel gauge to read full. As fuel level decreases, the float and arm move down. This increases the sending unit resistance causing the fuel gauge to read empty.

FUEL HEATER

Fuel Heater Location:

The fuel heater is used to prevent diesel fuel from waxing during cold weather operation. The fuel heater assembly is located in the top of the fuel filter housing.

Fuel Heater Temperature Sensor Location:

The heater/element assembly is equipped with a temperature sensor (thermostat) that senses fuel temperature. This sensor is attached to the fuel heater/element assembly (bottom view). When the temperature is below 45 ± 8 °F, the sensor allows current to flow to the heater element warming the fuel. When the temperature is above 75 ± 8 °F, the sensor stops current flow to the heater element.

Battery voltage to operate the fuel heater element is supplied from the ignition switch and through the fuel heater relay. Also refer to Fuel Heater Relay.

The fuel heater element and fuel heater relay are not computer controlled.

The heater element operates on 12 volts, 300 watts at 0 °F.

FUEL HEATER RELAY
Battery voltage to operate the fuel heater element is supplied from the ignition switch through the fuel heater relay. The fuel heater element and fuel heater relay are not computer controlled.

Power Distribution Center Location:

The fuel heater relay is located in Power Distribution Center (PDC). Refer to label on inside of PDC cover for relay location.

FUEL TRANSFER (LIFT) PUMP

Fuel Transfer Pump Location:

Engine Control Module (ECM) Location:

The fuel transfer pump (fuel lift pump) is located on the left-rear side of the engine cylinder block above the starter motor. The 12-volt electric vane-type pump is operated and controlled by the Engine Control Module (ECM). The ECM is bolted to the left side of the engine block behind the fuel filter.

The purpose of the fuel transfer pump is to supply (transfer) a low-pressure fuel source: from the fuel tank, through the fuel filter/water separator and to the fuel injection pump. Here, the low-pressure is raised to a high-pressure by the fuel injection pump for operation of the high-pressure fuel injectors. Check valves within the pump, control direction of fuel flow and prevent fuel bleed-back during engine shut down.

Normal current flow to the pump is 12 amperes.

With the engine running, the pump has 2 modes of operation: Mode 1: 100 percent duty-cycle with a minimum pressure of 10 psi except when the engine is cranking. Mode 2: 25 percent duty-cycle with minimum pressure of 7 psi with the engine cranking

The 25 percent duty-cycle is used to limit injection pump inlet pressure until the engine is running.

The transfer pump is self-priming: When the key is first turned on (without cranking engine), the pump will operate for approximately 2 seconds and then shut off. The pump will also operate for up to 25 seconds after the starter is engaged, and then disengaged and the engine is not running. The pump shuts off immediately if the key is on and the engine stops running.

Injection Pump Overflow Valve Location:

The fuel volume of the transfer pump will always provide more fuel than the fuel injection pump requires. Excess fuel is returned from the injection pump through an overflow valve. The valve is located on the side of the injection pump. It is also used to connect the fuel return line to the side of the injection pump. This valve opens at approximately 97 kPa (14 psi) and returns fuel to the fuel tank through the fuel return line.

FUEL TANK
The fuel tank is similar to the tank used with gasoline powered models. The tank is equipped with a separate fuel return line and a different fuel tank module for diesel powered models. A fuel tank mounted, electric fuel pump is not used with diesel powered models. Refer to Fuel Tank Module for additional information.

FUEL FILTER/WATER SEPARATOR
The fuel filter/water separator protects the fuel injection pump by removing water and contaminants from the fuel. The construction of the filter/separator allows fuel to pass through it, but helps prevent moisture (water) from doing so. Moisture collects at the bottom of the canister.

Fuel Filter/Water Separator Location:

The fuel filter/water separator assembly is located on left side of engine above starter motor. The assembly also includes the fuel heater and Water-In-Fuel (WIF) sensor.

For draining of water from canister, refer to Fuel Filter/Water Separator Removal/Installation.

A Water-In-Fuel (WIF) sensor is attached to side of canister. Refer to Water-In-Fuel Sensor Description/Operation.

The fuel heater is installed into the top of the filter/separator housing. Refer to Fuel Heater Description/Operation.

FUEL SYSTEM PRESSURE WARNING

WARNING: HIGH-PRESSURE FUEL LINES DELIVER DIESEL FUEL UNDER EXTREME PRESSURE FROM THE INJECTION PUMP TO THE FUEL INJECTORS. THIS MAY BE AS HIGH AS 120,000 KPA (17,405 PSI) USE EXTREME CAUTION WHEN INSPECTING FOR HIGH-PRESSURE FUEL LEAKS. INSPECT FOR HIGH-PRESSURE FUEL LEAKS WITH A SHEET OF CARDBOARD. HIGH FUEL INJECTION PRESSURE CAN CAUSE PERSONAL INJURY IF CONTACT IS MADE WITH THE SKIN.

FUEL INJECTION PUMP

Bosch VP44 Fuel Injection Pump:

Fuel Injection Pump Location:

The Bosch VP44 fuel injection pump is a solenoid-valve controlled-radial-piston-distributor type pump. The pump is mounted to the rear of the timing gear housing on the left side of engine.

The injection pump is driven by the engine camshaft. A gear on the end of the pump shaft meshes with the camshaft gear. The pump is timed to the engine. The VP44 is controlled by an integral (and non-serviceable) Fuel Pump Control Module (FPCM). The FPCM can operate the engine as an engine controller if a Crankshaft Position Sensor (CKP) signal is not present.

Fuel from the transfer (lift) pump enters the VP44 where it is pressurized and then distributed through high-pressure lines to the fuel injectors. The VP44 is cooled by the fuel that flows through it. A greater quantity of fuel is required for cooling the VP44 than what is necessary for engine operation. Because of this, approximately 70 percent of fuel entering the pump is returned to the fuel tank through the overflow valve and fuel return line. Refer to Overflow Valve Description/Operation for additional information.

The VP44 is not self-priming. At least two fuel injectors must be bled to remove air from the system. when servicing the fuel system, disconnecting components up to the pump will usually not require air bleeding from the fuel system. However, removal of the high-pressure lines, removal of the VP44 pump, or allowing the vehicle to completely run out of fuel, will require bleeding air from the high-pressure lines at the fuel injectors.

VP44 timing is matched to engine timing by an offset keyway that fits into the pump shaft. This key-way has a stamped number on it that is matched to a number on the VP44 pump (each keyway is calibrated to each pump).

When removing/installing the VP44, the same numbered keyway must always be installed. Also, the arrow on the top of the keyway should be installed pointed to the rear of pump.

Because of electrical control, the injection pump high and low idle speeds are not adjustable. Also, adjustment of fuel pump timing is not required and is not necessary.

FUEL INJECTORS

Fuel Injector Location:

Six individual, high-pressure fuel injectors are used. The injectors are vertically mounted into a bored hole in the top of the cylinder head. This bored hole is located between the intake/exhaust valves.

High-pressure fuel is supplied from the injection pump, through a high-pressure fuel line, through a steel connector and into the fuel injector. When fuel pressure rises to approximately 31,026 kPa (4,500 psi), the needle valve spring tension is overcome. The needle valve rises and fuel flows through the spray holes in the nozzle tip into the combustion chamber. The pressure required to lift the needle valve is the nozzle opening pressure. This is sometimes referred to as the "pop" pressure setting.

Fuel Injector Connections:

Each fuel injector is connected to each high-pressure fuel line with a steel connector. This steel connector is positioned into the cylinder head and sealed with an O-ring. The connectors are sealed to the high-pressure fuel lines with fittings. The ferrule on the end of the high-pressure fuel line pushes against the steel connector when the fuel line fitting is torqued into the cylinder head. This torquing force provides a sealing pressure between both the fuel line-to-connector and the fuel connector-to-fuel injector. The fitting torque is very critical. If the fitting is under torqued, the mating surfaces will not seal and a high-pressure fuel leak will result. If the fitting is over torqued, the connector and injector Will deform and also cause a high-pressure fuel leak. This leak will be inside the cylinder head and will not be visible. The result will be a possible fuel injector miss-fire and low power.

Fuel Injector Spray Pattern:

The fuel injectors use hole type nozzles. High-pressure flows into the side of the injector and causes the injector needle to lift and fuel to be injected. The clearances in the nozzle bore are extremely small and any sort of dirt or contaminants will cause the injector to stick. Because of this, it is very important to do a thorough cleaning of any lines before opening up any fuel system component. Always cover or cap any open fuel connections before a fuel system repair is performed.

Fuel Injector Edge Filter:

Each fuel injector connector tube contains an edge filter that breaks up small contaminants that enter the injector. The edge filter uses the injectors pulsating high-pressure to break up most particles so they are small enough to pass through the injector. The edge filters are not a substitute for proper cleaning and covering of all fuel system components during repair.

The bottom of each fuel injector is sealed to the cylinder head with a 1.5mm thick copper shim (gasket). The correct thickness shim must always be re-installed after removing an injector.

Fuel pressure in the injector circuit decreases after injection. The injector needle valve is immediately closed by the needle valve spring and fuel flow into the combustion chamber is stopped. Exhaust gases are prevented from entering the injector nozzle by the needle valve.

QUICK-CONNECT FITTINGS
Different types/sizes of quick-connect fittings are used to attach various fuel system components. These may be: a single-tab type, a two-tab type or a plastic retainer ring-type. Most fittings on diesel applications are the two-tab type. Refer to Quick-Connect Fittings Removal/Installation for more information.

CAUTION: The interior components (O-rings, spacers) of quick-connect fittings are not serviced separately, but new clips are available for some types. Do not attempt to repair damaged fittings or fuel lines/tubes. If repair is necessary, replace the complete fuel tube assembly.

LOW-PRESSURE FUEL LINES
All fuel lines up to the fuel injection pump are considered low-pressure. This includes the fuel lines from: the fuel tank to the fuel transfer pump, and the fuel transfer pump to the fuel injection pump. The fuel return lines, the fuel drain manifold and the fuel drain manifold lines are also considered low-pressure lines. High-pressure lines are used between the fuel injection pump and the fuel injectors. Also refer to High-Pressure Fuel Lines Description/Operation.

HIGH-PRESSURE FUEL LINES

High Pressure Fuel Lines:

The high-pressure fuel lines are the 6 lines located between the fuel injection pump and the fuel injector connector tubes. All other fuel lines are considered low-pressure lines.

CAUTION: The high-pressure fuel lines must be held securely in place in their holders. The lines cannot contact each other or other components. Do not attempt to weld high-pressure fuel lines or to repair lines that are damaged. If lines are ever kinked or bent, they must be replaced. Use only the recommended lines when replacement of high-pressure fuel line is necessary.

High-pressure fuel lines deliver fuel under pressure of up to approximately 120,000 kPa (17,405 PSI) from the injection pump to the fuel injectors. The lines expand and contract from the high-pressure fuel pulses generated during the injection process. All high-pressure fuel lines are of the same length and inside diameter. Correct high-pressure fuel line usage and installation is critical to smooth engine operation.

WARNING: USE EXTREME CAUTION WHEN INSPECTING FOR HIGH-PRESSURE FUEL LEAKS. INSPECT FOR HIGH-PRESSURE FUEL LEAKS WITH A SHEET OF CARDBOARD. HIGH FUEL INJECTION PRESSURE CAN CAUSE PERSONAL INJURY IF CONTACT IS MADE WITH THE SKIN.

FUEL DRAIN MANIFOLD PASSAGE

Fuel Drain Manifold Passage:

When the engine is running, and during injection, a small amount of fuel flows past the injector nozzle and is not injected into the combustion chamber. This fuel is used to lubricate the fuel injectors. Excess fuel drains into the fuel drain manifold (or passage). The fuel drain manifold is actually a rifled passage within the cylinder head. Fuel is drained from this passage into a line at the rear of the cylinder head. After exiting the cylinder head, fuel is routed (returned) back to the fuel tank. A "T" is installed into the fuel return line. This "T" is used to allow excess fuel from the injection pump to be returned into the fuel tank. A one-way check valve within the overflow valve prevents fuel (from the fuel drain manifold) from entering the fuel injection pump.

A small amount of fuel is returned from the fuel injectors, while a large amount (about 70% of supplied fuel) is returned from the fuel injection pump.

OVERFLOW VALVE

Overflow Valve Location:

Fuel volume from the fuel transfer (lift) pump will always provide more fuel than the fuel injection pump requires. The overflow valve (a check valve) is used to route excess fuel through the fuel return line and back to the fuel tank. Approximately 70% of supplied fuel is returned to the fuel tank. The valve is located on the side of the injection pump. It is also used to connect the fuel return line (banjo fitting) to the fuel injection pump. The valve opens at approximately 97 kPa (14 psi). If the check valve within the assembly is sticking open, fuel drainage of the injection pump could cause low engine power. Hard starting may also result.

If a Diagnostic Trouble Code (DTC) has been stored for "decreased engine performance due to high injection pump fuel temperature", the overflow valve may be stuck in closed position.