3100 HEUI Diesel Truck Engine Fuel System

Fuel System Schematic
(AA) High pressure oil line. (BB) Unit injector wiring harness. (CC) Low pressure oil supply line. (DD) Fuel line. (EE) Low pressure oil return line. (1) High pressure oil manifold. (2) High pressure oil line. (3) Hydraulic electronic unit injector. (4) Unit injector wiring harness. (5) Electronic control module (ECM). (6) Fuel pressure regulator. (7) Fuel filter. (8) Fuel transfer pump. (9) Fuel return line. (10) Injection actuation pressure control valve (IAPCV). (11) Electrical signal from ECM to IAPCV (controls oil manifold pressure). (12) Oil cooler. (13) Secondary oil filter. (14) Low pressure oil supply line. (15) High pressure oil pump. (16) Fuel line. (17) Fuel tank. (18) Low pressure oil return line. (19) Oil sump. (20) Oil pump (engine lubrication).


Fuel System Components
(1) High pressure oil manifold. (5) ECM. (7) Fuel filter. (8) Fuel transfer pump. (10) Injection actuation pressure control valve. (15) High pressure oil pump. (21) Injection actuation pressure sensor.

The 3100 HEUI fuel system uses Hydraulic Electronic Unit Injectors (3). Hydraulic Electronic Unit Injectors (3) use high pressure oil instead of using a separate cam lobe to pressurize the unit injector.

The fuel supply circuit is a conventional design for unit injected engines, in that it uses a single piston type fuel transfer pump (8) which circulates fuel at low pressure, first through the fuel filter (7) and then into the cylinder head fuel passages at low pressure. Fuel is delivered at high pressure into the combustion chamber through hydraulic electronic unit injectors (3). The unit injectors are located near the center of the combustion chambers in the cylinder head between the rocker arms.

Fuel drawn from fuel tank (7) by the fuel transfer pump (8) is typically passed through an OEM installed primary filter of approximately thirty micron rating. Some OEMs may install a combination filter/water separator. The fuel transfer pump (8) incorporates a check valve to permit fuel flow for hand priming and a pressure regulating valve to protect the system from extreme pressure.

From the fuel transfer pump (8), fuel passes through a secondary fuel filter (7) of two micron rating, and then to the fuel manifold fitting at the front of the engine.

Fuel flows continuously around each unit injector through an internal passage running the length of the head, exiting at the rear of the engine through a pressure regulator to return to the fuel tank (17). Excess fuel not being used for injection helps to cool the unit injectors and to purge air from the system. During normal under load operating conditions, fuel pressure is maintained in the range of 400 kPa (58 psi) to 525 kPa (76 psi) by an orificed pressure regulating valve at the rear of the cylinder head, which also contains a check valve and serves as a siphon break. Fuel pressure at low idle should be a minimum of 500 kPa (73 psi).

When the ECM (5) activates each unit injector the engine oil in the high pressure oil manifold (1) acts on a piston in the upper part of the unit injector. This piston has an area roughly six times the area of the unit injector plunger. Fuel is injected into the cylinder at 138 000+ kPa (20 000+ psi).

The ECM (5) is located at the rear on the left side of the engine. The system provides total electronic control of the start and duration of the fuel injection. The ECM (5) uses engine data gathered by several sensors to make adjustments on fuel delivery based on the programmed performance map used in the engine control software.

The high pressure oil pump (15) is located at the left front corner of the engine. The high pressure oil pump (15) is a gear-driven axial piston pump. It raises the engine oil pressure level from typical engine operating oil pressure level to the actuation pressure level required by the unit injectors.

The injection actuation pressure control valve (10) is located in the high pressure oil pump (15) at the top left of the engine. Operational maps stored in the module’s memory identify the optimum oil pressure for the best performance.

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