Unit injector hydraulic pump -807640087

TM 9-2320-312-24-2

Systems Operation Section

Fuel Transfer Pump

Some engines use Engine Control Modules

(ECM) (15) with a replaceable computer chip.

The software has already been installed in the

Fuel transfer pump (35) is mounted on the back of

replaceable computer chip. The 3126B and 3126E

unit injector hydraulic pump (1). The fuel transfer

diesel truck engines do not have a replaceable

pump is used in order to draw fuel from fuel tank

personality module. The 3126B and 3126E diesel

(12). Also, the fuel transfer pump is used in order

truck engine's personality module are a permanent

to pressurize the fuel to 450 kPa (65 psi). The

part of the ECM. The 3126B and 3126E diesel truck

pressurized fuel is supplied to injectors (7).

engine's personality module can be reprogrammed.

Reprogramming of the personality module requires

Fuel transfer pump (35) is a single piston pump

the use of Caterpillar Electronic Technician (Cat

that is spring loaded. The shaft of the unit injector

ET). The flash function of Cat ET will be used during

hydraulic pump provides power to the transfer

the reprogramming.

pump through an off-center bearing. There are two

check valves in the fuel transfer pump. The inlet

ECM (15) logs faults of engine performance. Also,

check valve opens in order to allow fuel from the

the ECM is capable of running several diagnostic

tank into the pump. The inlet check valve closes in

tests automatically when the ECM is used with an

order to prevent fuel leakage back to the fuel tank.

electronic service tool such as the Cat ET.

The outlet check valve opens in order to supply fuel

to the fuel supply passage. The fuel supply passage

is located in the cylinder head. The fuel supply

Unit injector hydraulic pump

passage supplies fuel to injectors (7). The outlet

check valve closes in order to prevent pressurized

Unit injector hydraulic pump (1) (high pressure

fuel leakage back through the pump.

oil pump) is located at the left front corner of the

engine. The unit injector hydraulic pump is a piston

Injection Actuation Pressure Sensor

pump that has a fixed displacement. The unit

injector hydraulic pump uses an axial piston. The

(IAP)

unit injector hydraulic pump uses a portion of the

engine lubrication oil. The unit injector hydraulic

IAP Sensor (6) is installed in the high pressure oil

pump pressurizes the engine lubrication oil to the

manifold. The high pressure oil manifold supplies

injection actuation pressure that is required in order

actuation oil in order to power the unit injectors. The

to power the HEUI injectors.

IAP Sensor monitors injection actuation pressure.

The IAP Sensor sends a continuous voltage signal

Injection Actuation Pressure Control

back to ECM (15). The ECM interprets the signal.

The ECM is aware of the injection actuation pressure

Valve (IAP Control Valve)

at all times.

Injection actuation pressure control valve (10) (IAP

Control Valve) is located on the side of unit injector

hydraulic pump (1). Under most conditions, the

pump is producing excess oil flow. The IAP Control

Valve discharges excess pump flow to the drain

in order to control injection actuation pressure to

the desired level. The IAP Control Valve is a valve

of high precision that controls the actual actuation

pressure. The performance maps of ECM (15)

contain a desired actuation pressure for every

engine operating condition. The ECM sends a

control current to the IAP Control Valve. The control

current should make the actual actuation pressure

equal to the desired actuation pressure.

IAP Control Valve (10) is an actuator. The IAP

Control Valve converts an electrical signal from

ECM (15) to the mechanical control of a spool valve

in order to control pump outlet pressure.