User Manual

Injection Actuation Pressure Sensor (IAP)
The IAP Sensor monitors injection actuation pressure. The IAP Sensor sends a continuous voltage signal back
to the ECM . The ECM interprets the signal. The ECM is aware of the injection actuation pressure at all times.
The ECM analyzes the voltage from the sensor. The ECM then adjusts the current to the solenoid.
HEUI Fuel System
Low Pressure Fuel System
(1) Unit injector hydraulic pump
(2) Fuel transfer pump
(3) Hydraulic electronic unit injector
(4) Secondary fuel filter
(5) Primary fuel filter and water separator
(6) Fuel tank
(7) Fuel pressure regulator
The low pressure fuel system serves two
functions. The low pressure fuel system
supplies fuel for combustion to injectors.
The low pressure fuel system also supplies
excess fuel flow in order to remove air
from the system.
The low pressure fuel system consists of five basic components:
• Fuel tank
• Primary fuel filter/water separator
• Two micron secondary fuel filter
• Fuel transfer pump
• Fuel pressure regulator
Fuel is drawn from the fuel tank and flows through a thirteen micron primary fuel filter/water separator. The
primary fuel filter/water separator removes large debris from the fuel. The primary filter element also separates
water from the fuel. The water is collected in the bowl at the bottom of the primary fuel filter/water separator.
Fuel flows from the primary fuel filter/water separator to the inlet side of fuel transfer pump. An inlet check
valve in the inlet port of the fuel transfer pump opens in order to allow the flow of fuel into the pump. After the
fuel flow has stopped, the inlet check valve closes in order to prevent fuel flow out of the inlet port. Fuel flows
from the inlet port in the pump to the outlet port. Pressurized fuel flows from the outlet port of the pump to the
two micron secondary fuel filter. A two micron secondary fuel filter is standard on all Caterpillar engines.
These fuel filters are high efficiency. This filter removes very small abrasive contaminants from the fuel.