C-10 and C-12 Truck Engines Caterpillar

Illustration 1	g00914507
(1) Camshaft position sensor (2) Injectors (3) Crankshaft position sensor (4) Retarder solenoid (5) Boost pressure sensor (6) Fuel supply rail (7) Atmospheric pressure sensor (8) 2 Micron secondary fuel filter (9) Fuel temperature regulator (10) Engine oil pressure sensor (11) Fuel pump (12) Primary fuel filter (13) Fuel tank (14) Engine coolant temperature sensor (15) Fuel pressure regulator (16) Accelerator pedal (17) Accelerator pedal position sensor (18) Batteries (19) ECM (20) Inlet air temperature sensor (21) SAE J1587/J1708 Data link (22) Fuel temperature sensor (23) SAE J1939 Data link (24) SAE J1922/J1708 Data link (25) Ambient air temperature (26) Timing calibration connector (27) Warning and check engine lamps (28) 2 Lamp outputs (29) 6 Programmable outputs (30) Engine coolant level sensor (31) Cooling fan relay or solenoid (32) Vehicle speed sensor (33) Speedometer & tachometer (34) PTO on/off switch and PTO set/resume switch (35) Cruise on/off switch and cruise set/resume switch (36) 7 Programmable inputs (37) Service brake pedal position switches. (38) Engine retarder switch (39) Keyswitch (40) Neutral & clutch pedal position switches

The Electronic Unit Injector system consists of the following systems: the mechanical system and the electronic system. The mechanical system is made up of the low pressure fuel supply system and the electronic unit injectors. The electronic system provides complete electronic control of all engine functions. The electronic control system consists of the following three types of components: input, control and output.

Most changes to engine horsepower or to the performance are accomplished by installing new electronic software or upgrading mechanical components.

There are five major components of the Electronic Unit Injector fuel system:

• Electronic Unit Injectors

• Fuel transfer pump

• Electronic Control Module

• Sensors

• Actuators

The Electronic Unit Injectors produce fuel injection pressures up to 207000 kPa (30000 psi). The Electronic Unit Injectors also fire up to 19 times per second at rated speed. The fuel transfer pump supplies the injectors by drawing fuel from the tank and by pressurizing the tank between 60 and 125 PSI. The ECM is a powerful computer which controls all major engine functions. Sensors are electronic devices which monitor engine performance parameters. Engine performance parameters measure pressure, temperature and speed. This information is sent to the ECM via a signal voltage. Actuators are electronic devices which use electronic currents from the ECM to change engine performance. An example of an actuator is the Injector solenoid.

Low Pressure Fuel System

Illustration 2	g00915523
(2) Injectors (6) Fuel supply rail (8) 2 Micron secondary fuel filter (9) Fuel temperature regulator (11) Fuel pump (12) Primary fuel filter (13) Fuel tank (15) Fuel pressure regulator (41) Electronic sensors and switches

The low pressure fuel system supplies fuel from the fuel tank to the injectors. The low pressure fuel system has four basic functions:

• The low pressure fuel system supplies fuel to the injectors for combustion.

• The low pressure fuel system supplies fuel to the injectors for cooling.

• The low pressure fuel system supplies fuel to the fuel system in order to remove air.

• The low pressure fuel system combines cold fuel from the fuel tank and warm fuel from the fuel return line during cold starts.

The major parts in a low pressure fuel system consist of the following components:

• Fuel tank

• Fuel transfer lines

• Primary fuel filter or water separator

• Fuel transfer pump

• Secondary fuel filter

• Fuel priming pump

• Fuel pressure regulator valve

• Fuel temperature regulator valve

The electronic unit injectors, the fuel transfer pump, the ECM, sensors, and actuators are part of the low pressure fuel system.

In the low pressure fuel system, the fuel is pulled from the fuel tank to the primary fuel filter or to the water separator. The primary fuel filter removes large debris from the fuel before the fuel flows into the transfer pump. The fuel transfer pump is a gear pump that contains a pressure relief valve. Fuel flows from the outlet port of the transfer pump to the secondary fuel filter. All 1999 and newer engines use a 2 micron fuel filter. The 2 micron filter removes small abrasive contaminants from the fuel system, which can cause damage to the unit injectors.

The fuel filter base contains a hand operated fuel priming pump. The fuel priming pump removes air from the system when a fuel filter has been changed or a unit injector has been changed. The priming pump pulls fuel from the tank, around the transfer pump and into the filter. The transfer pump pushes fuel through the supply passage in the cylinder head and back to the tank.

The fuel pressure regulator consists of a spring loaded check valve. The pressure relief valve opens at approximately 60 to 125 PSI. When the engine is in the off position and the fuel pressure drops below 60 PSI, the check valve closes. The check valve closes in order to prevent the fuel in the cylinder head from draining back into the fuel tank. Retaining the fuel in the head maintains a supply of fuel for the injectors during start-up requirement.

The fuel temperature regulator valve is used to supply the injectors with warm fuel during cold operation. The injectors pick up the fuel from a fuel passage in the cylinder head. The injectors are supplied with an excess of fuel that is returned to the fuel tank. This excess fuel that is returned to the fuel tank is warm. There is a temperature difference between the return fuel and the fuel in the tank. The temperature difference decreases as the two begin to mix. The MBL1-UP and MBJ1-UP engines are equipped with an extra fuel line that provides a connection for the fuel return line and the fuel transfer pump. The valve in the extra fuel line is controlled by temperature. The temperature control valve opens when the fuel is cold. This allows the excess warm fuel from the cylinder head to mix with the cold fuel from the tank. The warm fuel increases injector life.

The ECM controls major engine functions. Sensors are electronic devices that monitor engine performance parameters. The pressure sensor, the temperature sensor and the speed sensor provide information to the ECM by a signal voltage. Actuators are electronic devices which use electrical currents from the ECM to change engine performance. An example of an actuator is an injector solenoid.

Electronic Controls

The electronic control system provides complete electronic control of all engine functions. The electronic control system consists of the following three types of components: input, control and output. Sensors monitor engine operating conditions. This information is sent to the ECM. The ECM has three main functions. The ECM provides power for the engine electronics and monitors input signals from the engine sensors. The ECM also acts as a governor to control engine rpm. The ECM stores active faults, logged faults, and logged events. The Personality Module is the software in the ECM which contains the specific maps that define power, torque, and RPM of the engine. The ECM sends electrical current to the output components in order to control engine operation. The ECM has the following connectors: two 70 pin harness connectors, one engine harness connector and one vehicle harness connector. The vehicle harness connects the ECM to the engine control portion of the vehicle harness. The engine control portion includes the following components.

• Accelerator pedal position sensor

• Vehicle speed sensor

• Transmission

• Brake

• Clutch switches

• Cruise control

• PTO switch

• Data links

• Check engine light

• Warning light

• Engine retarder switch

• Speedometer

• Tachometer

• Cooling fan solenoid

The following list of features are part of the electronic control system:

• Cold start strategy

• Oil pressure

• Coolant temperature warning indicator

• Automatic altitude compensation

• Variable injection timing

• Electronic engine speed governing

These features result in the following items: precise engine speed control, very little smoke, faster cold starting and built-in engine protection.

The ECM consists of the following two main components: the ECM and the personality module.

The ECM is a computer and the personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:

• Horsepower

• Torque curves

• Rpm

• Other characteristics

The ECM, the personality module, the sensors, and the unit injectors work together in order to control the engine. The ECM, the personality module, the sensors, and the unit injectors can not control the engine alone.

The ECM determines a desired rpm that is based on the following criteria:

• Throttle signal

• Certain diagnostic codes

• Vehicle speed signal

The ECM maintains the desired engine rpm by sensing the actual engine rpm. The ECM calculates the fuel amount that needs to be injected in order to achieve the desired rpm.

Fuel Injection Timing and Delivery

The ECM controls the injected fuel amount by varying the signals to the unit injectors. The unit injectors will inject fuel ONLY if the unit injector solenoid is energized. The ECM sends a 90 volt signal to the solenoid for energizing the solenoid. By controlling the timing of the 90 volt signal, the ECM controls injection timing. By controlling the duration of the 90 volt signal, the ECM controls the injected fuel amount.

Injection timing is determined by engine rpm, and other engine data. The ECM senses the top center position of cylinder number 1 from the signal that is provided by the engine speed sensor. The ECM decides when the injection should occur relative to the top center position. The ECM provides the signal to the unit injector at the desired time.

Unit Injector Mechanism

Illustration 3	g00908926
Typical examples of Electronic Unit Injector fuel systems. (1) Adjusting nut (2) Rocker arm assembly (3) Unit injector (4) Pushrod

Injection Actuation System

The unit injector pressurizes the fuel. The correct amount of fuel is then injected into the cylinder block at precise times. The ECM determines the injection timing and the amount of fuel that is delivered. The unit injector is operated by a camshaft lobe and a rocker arm. The camshaft has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and the other lobe operates the unit injector mechanism. Force is transferred from the unit injector lobe on the camshaft through the lifter to the pushrod (4). The force of the pushrod is transferred through rocker arm assembly (2) and to the top of the unit injector. The adjusting nut (1) allows setting of the unit injector adjustment. Refer to Systems Operation/Testing and Adjusting, "Electronic Unit Injector - Adjust" for the proper setting of the unit injector adjustment.

Unit Injector

Illustration 4	g00626752
(1) Solenoid (2) Tappet (3) Plunger (4) Barrel (5) Nozzle Assembly

Operation of the Fuel Injector

The operation of the Electronic Control Unit (EUI) consists of the following four stages: Pre-injection, Injection, End of injection and Fill. Unit injectors use a plunger and barrel to pump high pressure fuel into the combustion chamber. Components of the injector include the tappet, the plunger, the barrel and nozzle assembly. Components of the nozzle assembly include the spring, the nozzle check, and a nozzle tip. The cartridge valve is made up of the following components: solenoid, armature, poppet valve and poppet spring.

The injector is mounted in an injector bore in the cylinder head which has an integral fuel supply passage. The injector sleeve separates the injector from the engine coolant in the water jacket. Some engines use a stainless steel sleeve. The stainless steel sleeve fits into the cylinder head with a light press fit.

Illustration 5	g00660656
Pre-injection (A) Fuel supply pressure (B) Injection pressure (C) Moving parts (D) Mechanical movement (E) Fuel movement.

Pre-injection metering starts with the injector plunger and the injector tappet at the top of the fuel injection stroke. When the plunger cavity is full of fuel, the poppet valve is in the open position and the nozzle check is in the open position. Fuel leaves the plunger cavity when the rocker arm pushes down on the tappet and the plunger. Fuel flow that is blocked by the closed nozzle check valve flows past the open poppet valve to the fuel supply passage in the cylinder head. If the solenoid is energized, the poppet valve remains open and the fuel from the plunger cavity continues flowing into the fuel supply passage.

Illustration 6	g00660658
Injection (A) Fuel supply pressure. (B) Injection pressure (C) Moving parts (D) Mechanical movement (E) Fuel movement.

To start injection, the ECM sends a current to the solenoid on the cartridge valve. The solenoid creates a magnetic field which attracts the armature. When the solenoid is energized, the armature assembly will lift the poppet valve so the poppet valve contacts the poppet seat. This is the closed position. Once the poppet valve closes, the flow path for the fuel that is leaving the plunger cavity is blocked. The plunger continues to push fuel from the plunger cavity and the fuel pressure builds up. When the fuel pressure reaches approximately 34500 kPa (5000 psi), the force of the high pressure fuel overcomes the spring force. This holds the nozzle check in the closed position. The nozzle check moves off the nozzle seat and the fuel flows out of the injector tip. This is the start of injection.

Illustration 7	g00660660
End of injection (A) Fuel supply pressure (C) Moving parts

Injection is continuous while the injector plunger moves in a downward motion and the energized solenoid holds the poppet valve closed. When injection pressure is no longer required, the ECM stops current flow to the solenoid. When the current flow to the solenoid stops, the poppet valve opens. The poppet valve is opened by the fuel injector spring and the fuel pressure. High pressure fuel can now flow around the open poppet valve and into the fuel supply passage. This results in a rapid drop in injection pressure. When the injection pressure drops to approximately 24000 kPa (3500 psi), the nozzle check closes and injection stops. This is the end of injection.

Illustration 8	g00795649
Fill (A) Fuel supply pressure (B) Injection pressure (C) Moving parts (D) Mechanical movement (E) Fuel movement.

When the plunger reaches the bottom of the barrel, fuel is no longer forced from the plunger cavity. The plunger is pulled up by the tappet and the tappet spring. The upward movement of the plunger causes the pressure in the plunger cavity to drop below fuel supply pressure. Fuel flows from the fuel supply passage around the open poppet and into the plunger cavity as the plunger travels upward. When the plunger reaches the top of the stroke, the plunger cavity is full of fuel and fuel flow into the plunger cavity stops. This is the beginning of pre-injection.