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Fuel Delivery and Air Induction: Description and Operation

FUEL DELIVERY - DIESEL
Diesel Fuel Delivery System
The fuel system on the Cummins 24 valve-Turbo Diesel Engine uses an electronically controlled fuel injection pump with three control modules.

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

Fig.1 Fuel System Components - Diesel:




Some fuel system components are shown in (Fig. 1).

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

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.

Fig.13 Fuel Heater Location:




FUEL FILTER / WATER SEPARATOR
The fuel filter/water separator assembly is located on left side of engine above starter motor (Fig. 13). The assembly also includes the fuel heater and Water-In-Fuel (WIF) sensor.

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.

Refer to the maintenance schedules for the recommended fuel filter replacement intervals.

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

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.

Fig.18 Fuel Heater Location:




FUEL HEATER
The fuel heater assembly is located on the side of the fuel filter housing (Fig. 18).

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.

The fuel heater is used to prevent diesel fuel from waxing during cold weather operation.

When the temperature is below 45 ± 8 degrees F, the temperature sensor allows current to flow to the heater element warming the fuel. When the temperature is above 75 ± 8 degrees 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 degrees F.

Fig.20 Power Distribution Center Location:




FUEL HEATER RELAY
The fuel heater relay is located in Power Distribution Center (PDC) (Fig. 20). Refer to label on inside of PDC cover for relay location.

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.

FUEL INJECTION PUMP

Fig.23 Fuel Injection Pump Dat Plate Location:




Fuel Pump 245 H.P.
Although the fuel injection pump on the 245 horsepower engine appears similar to other VP 44 injection pumps, there are internal differences that make it unique. If pump replacement is necessary be sure to verify pump number. The pump number can be found on the Fuel Injection Pump Data Plate (Fig. 23).

Fig.24 Fuel Injection Pump Location:




Fuel Pump 235 H.P.
The fuel injection pump is mounted to the rear of the timing gear housing on the left side of engine (Fig. 24).

Fig.25 Bosch VP44 Fuel Injection Pump:




The Bosch VP44 fuel injection pump (Fig. 25) is a solenoid-valve controlled-radial-piston-distributor type pump.

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) (Fig. 24). 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 over- flow 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 rearward towards the 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 LEVEL SENDING UNIT / SENSOR
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 (card).

The fuel tank module on diesel powered models has 3 different circuits (wires). Two of these circuits are used at the fuel gauge sending unit for fuel gauge operation. The other wire is used for a ground. The diesel engine does not have a fuel tank module mounted electric fuel pump. The electric fuel pump (fuel transfer pump) is mounted to the engine.

For Fuel Gauge Operation: A constant input voltage source of about 12 volts (battery voltage) is supplied to the resistor track on the fuel gauge sending unit. This is fed directly from the Powertrain Control Module (PCM). NOTE: For diagnostic purposes, this 12V power source can only be verified with the circuit opened (fuel tank module electrical connector unplugged). With the connectors plugged, output voltages will vary from about 0.6 volts at FULL, to about 7.0 volts at EMPTY The resistor track is used to vary the voltage (resistance) depending on fuel tank float level. As fuel level increases, the float and arm move up, which decreases voltage. As fuel level decreases, the float and arm move down, which increases voltage. The varied voltage signal is returned back to the PCM through the sensor return circuit.

Both of the electrical circuits between the fuel gauge sending unit and the PCM are hard-wired (not multi-plexed). After the voltage signal is sent from the resistor track, and back to the PCM, the PCM will interpret the resistance (voltage) data and send a message across the multi-plex bus circuits to the instrument panel cluster. Here it is translated into the appropriate fuel gauge level reading. Refer to Instrument Panel for additional information.

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.

Fig.48 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 (Fig. 45). 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 TANK
Diesel 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.

For removal and installation procedures, refer to Fuel Tank - Gasoline Engines.

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.

Fig.56 Top View Of Fuel Tank Module - Diesel:




The fuel tank module is installed in the top of the fuel tank (Fig. 56). The fuel tank module (Fig. 56) 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

Refer to Fuel Gauge Sending Unit.

FUEL TRANSFER PUMP

Fig.58 Fuel Transfer Pump Location:




Fig.59 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 (Fig. 58). The 12-volt electric vane-type pump is operated and controlled by the Engine Control Module (ECM) (Fig. 59).

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: 15 percent duty-cycle with maximum pressure of 7 psi with the engine cranking

The 15 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 1/4 second 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.

Fig.60 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 (Fig. 60). 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.

Fig.65 Overflow Valve Location:




OVERFLOW VALVE
The overflow valve is located on the side of the injection pump (Fig 65) It is also used to connect the fuel return line (banjo fitting) to the fuel injection pump.

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 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 hard starting.

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.

Fig.68 Water-in-fuel Sensor Location:




WATER IN FUEL SENSOR
The WIF sensor is located on the side of the fuel filter/water separator canister (Fig 68)

The sensor sends an input to the Engine Control Module (ECM) when it senses water in the fuel filter/water separator. As the water level in the filter/separator increases, the resistance across the WIF sensor decreases. This decrease in resistance is sent as a signal to the ECM and compared to a high water standard value. Once the value reaches 30 to 40 kilohms, the ECM will activate the water-in-fuel warning lamp through CCD bus circuits. This all takes place when the ignition key is initially put in the ON position. The ECM continues to monitor the input at the end of the intake manifold air heater post-heat cycle.

Fig.69 Fuel Drain Manifold Passage:




FUEL DRAIN MANIFOLD
The fuel drain manifold is actually a rifled passage within the cylinder head (Fig 69)

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). Fuel is drained from this passage into a line at the rear of the cylinder head (Fig. 69). After exiting the cylinder head, fuel is routed (returned) back to the fuel tank. A "T" is installed into the fuel return line (Fig. 69). This "T" is used to allow excess fuel from the injection pump to be returned into the fuel tank. A oneway 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.