Type I Fuel System
 | |
| Illustration 1 | g00712565 |
Fuel system schematic (A) Fuel priming pump (if equipped) (1) Screen (if equipped) (2) Inlet check valve (3) Fuel transfer pump that is integral with the governor (4) Outlet check valve (5) Fuel filter (6) Cylinder head (7) Pressure regulating orifice (8) Check valve (9) Primary fuel filter (if equipped) (10) Fuel tank | |
Fuel from fuel tank (10) is pulled through an in-line screen (1) by fuel transfer pump (3). The fuel transfer pump is integral with the governor. Fuel is sent from the fuel transfer pump through fuel filter (5) to a drilled passage in the cylinder head (6). The drilled passage in the cylinder head intersects a gallery around each unit injector in order to provide a continuous flow of fuel to all injectors. Unused fuel exits the cylinder head and passes through pressure regulating orifice (7) and check valve (8) before returning to fuel tank (10). Pressure regulating orifice (7) is located in the fuel return tube assembly. This pressure regulating orifice ensures adequate fuel gallery pressure for low idle fuel flows. Check valve (8) prevents fuel from leaving the cylinder head fuel gallery during engine shutdown.
When there is air on the inlet side of the fuel system, fuel priming pump (A) (if equipped) may be used in order to fill the fuel filter and the fuel gallery that is in the cylinder head. This is performed before the engine is started. When the priming pump is used, check valves that are located in the fuel priming pump control the movement of the fuel. The fuel is forced through the low pressure side of the fuel system. This removes air from the fuel lines and components back into the fuel tank.
 | |
| Illustration 2 | g00712706 |
Lines group for the fuel filter (3) Fuel transfer pump that is integral with the governor (5) Fuel filter (6) Cylinder head (11) Fuel outlet port to the fuel tank (12) Fuel inlet port to the fuel transfer pump (13) Fuel filter base (14) Pressure tap for filtered fuel (15) Tube assembly from the fuel filter base to the fuel gallery in the cylinder head (16) Tube assembly from the transfer pump to the fuel filter base | |
 | |
| Illustration 3 | g00712708 |
Lines group for the fuel filter (view (A-A) ) (1) Screen (if equipped) (6) Cylinder head (7) Pressure regulating orifice (8) Check valve (11) Fuel outlet port to the fuel tank (12) Fuel inlet port to the fuel transfer pump (16) Tube assembly from the transfer pump to the fuel filter base (17) Tube assembly from the fuel passage in the cylinder head to the fuel tank | |
Type II Fuel System
 | |
| Illustration 4 | g00690661 |
Fuel system schematic (A) Fuel priming pump (if equipped) (1) Screen (if equipped) (2) Inlet check valve (3) Fuel transfer pump that is integral with the governor (4) Outlet check valve (5) Fuel filter (6) Cylinder head (7) Pressure regulating orifice (8) Check valve (9) Primary fuel filter (if equipped) (10) Pressure relief valve (11) Fuel tank | |
Fuel from fuel tank (11) is pulled through an in-line screen (1) by fuel transfer pump (3). The fuel transfer pump is integral with the governor. Fuel is sent from the fuel transfer pump through the pressure relief valve (10). The pressure relief valve is closed in normal operation. Fuel will enter through fuel filter (9) to a drilled passage in the cylinder head (6). Once the pressure of the fuel is greater than the desired range then the pressure relief valve will open. This will allow the fuel to return to the tank. The drilled passage in the cylinder head intersects a gallery around each unit injector in order to provide a continuous flow of fuel to all injectors.
When there is air on the inlet side of the fuel system, fuel priming pump (A) (if equipped) may be used in order to fill the fuel filter and the fuel gallery that is in the cylinder head. This is performed before the engine is started. When the priming pump is used, check valves that are located in the fuel priming pump control the movement of the fuel. The fuel is forced through the low pressure side of the fuel system. This removes air from the fuel lines and components back into the fuel tank.
 | |
| Illustration 5 | g00690672 |
Lines group for the fuel filter (3) Fuel transfer pump that is integral with the governor (5) Fuel filter (6) Cylinder head (10) Pressure relief valve (12) Fuel outlet port to the fuel tank (13) Fuel inlet port to the fuel transfer pump (14) Fuel filter base (15) Pressure tap for filtered fuel (16) Tube assembly from the fuel filter base to the fuel gallery in the cylinder head (17) Tube assembly from the transfer pump to the fuel filter base | |
 | |
| Illustration 6 | g00690675 |
Lines group for the fuel filter (view (A-A) ) (1) Screen (if equipped) (6) Cylinder head (7) Pressure regulating orifice (8) Check valve (10) Pressure relief valve (12) Fuel outlet port to the fuel tank (13) Fuel inlet port to the fuel transfer pump (17) Tube assembly from the transfer pump to the fuel filter base (18) Tube assembly from the fuel passage in the cylinder head to the fuel tank | |
Fuel Heater And Water Separator (If Equipped)
 | |
| Illustration 7 | g00839038 |
Fuel heater and water separator (1) Fuel filter (2) Heater (3) Drain valve (water) (4) Temperature sensor | |
Some engines have a fuel heater and a water separator together. The fuel heater is controlled by a thermostat that is located in the base of the unit. The thermostat is preset in order to turn on the heater when the fuel temperature is below 2 °C (36 °F). The fuel heater will turn off when the fuel temperature is 7 °C (45 °F).
Water that has been separated from the fuel can be drained from the unit by lifting up on drain valve (3) .
Fuel Transfer Pump
 | |
| Illustration 8 | g00690711 |
Fuel transfer pump (A) Inlet flow of fuel (B) Outlet flow of fuel (1) Screen (if equipped) (2) Inlet check valve (3) Spring (4) Piston assembly (5) Outlet check valve (6) Piston check valve (7) Tappet assembly (8) Camshaft (9) Passage | |
The fuel transfer pump is located in the front housing of the governor. The pump is activated by camshaft (8) that is attached to the shaft of the governor drive gear. Piston assembly (4) and tappet assembly (7) are stroked up and down by the camshaft and spring (3) .
Fuel enters the transfer pump through screen (1) (if equipped) and inlet check valve (2). On the upstroke of piston assembly (4), inlet check valve (2) closes. Outlet check valve (5) closes in order to prevent fuel from being pulled back in the pump from the outlet. As pressure increases above piston assembly (4), piston check valve (6) opens in order to fill the cavity above the piston assembly.
On the downstroke, as the fuel pressure in passage (9) increases, piston check valve (6) is closed and outlet check valve (5) is opened. This causes fuel to be pushed through the secondary fuel filter and to the engine. Inlet check valve (2) opens in order to allow fuel to fill the cavity above piston assembly (4) .
During engine shutdown, the check valves are held closed by springs.
Fuel Injection Pump (Unit Injector)
 | |
| Illustration 9 | g00691325 |
Fuel injection system (1) Rocker arm (2) Setscrew (3) Floating button (4) Tappet Spring (5) Push rod (6) Plunger (7) Rack (8) O-ring (9) Barrel (10) Fuel gallery (11) Sleeve (12) O-ring (13) Lifter (14) Camshaft | |
The fuel injection pump (unit injector) allows a small amount of fuel to be injected at the proper time into the combustion chamber. The fuel is supplied by fuel gallery (10) that surrounds each unit injector. Each of these galleries are connected by a drilled passage in the cylinder head. This passage provides a continuous flow of fuel to all unit injectors.
The unit injector is isolated from the coolant passages by sleeve (11). The sleeve also provides the seating surface for the unit injector.
Injection timing is determined by the angular location of camshaft (14) and the vertical location of plunger (6) in barrel (9). The angular location of the camshaft is controlled by the camshaft-to-crankshaft gear mesh at the front of the engine. The location of the plunger (fuel timing) is adjusted by setscrew (2) .
The profile of the camshaft is sent to rocker arm (1) by lifter (13) and push rod (5), as the camshaft rotates. The motion of rocker arm (1) is then sent to plunger (6) through the floating button (3).
 | |
| Illustration 10 | g00691353 |
Fuel injection pump (unit injector) (4) Tappet spring (6) Plunger (7) Rack (8) O-ring (9) Barrel (12) O-ring (15) Gear (16) Sleeve filter (17) Helix (18) Lower port (19) Upper port (20) Spring (21) Check (needle valve) | |
At the top of the plunger's stroke, fuel from fuel gallery (10) enters the unit injector around the edges of sleeve filter (16). The fuel then fills the volume below plunger (6) .
During the plunger's downward motion, fuel beneath the plunger is displaced into the gallery through the two ports in barrel (9). As upper port (19) is closed by the bottom edge of the plunger, fuel continues to be displaced through lower port (18). When the lower port is closed, effective stroke begins. The fuel inside the unit injector becomes pressurized by the continued downward movement of the plunger. When the fuel pressure is sufficient to open check (21), high pressure fuel will be forced through orifices at the bottom of the nozzle into the combustion chamber. This will continue until upper port (19) is uncovered by helix (17) on the plunger. At this instant, effective stroke ends and this high pressure fuel will spill through upper port (19) into the gallery. This will allow spring (20) to close check (21), which will end the injection cycle.
The downward motion of the plunger will continue until lifter (13) reaches the nose of the camshaft. The plunger will be returned upward by tappet spring (4). This will allow the cavity under the plunger to be refilled from the fuel in the gallery. The unit injector is now ready for the next cycle.
In addition to vertical motion, the plunger can rotate with respect to barrel (9) by gear (15). The gear slides in order to allow vertical movement of the plunger and the gear meshes with rack (7). The rotation of the gear changes the relationship between helix (17) and upper port (19). The amount of fuel that is injected into each combustion chamber then changes. for example, If rack (7) is moved to the right, then plunger (6) will rotate CCW. (This movement is viewed from the top.) The distance between the bottom end of the plunger and helix (17) then increases with respect to upper port (19). The effective stroke is increased and more fuel is injected into the combustion chamber.
Control Linkage for the Fuel Injection Rack
 | |
| Illustration 11 | g00691511 |
Unit injectors and rack control linkage (1) Shaft (2) Torsion spring (3) Clamp (4) Lever assembly (5) Link (6) Fuel setting screw (7) Lever assembly (8) Synchronization screw (9) Rack (10) Clamp (11) Unit injector | |
 | |
| Illustration 12 | g00691611 |
Unit injector and rack control linkage (A) FUEL ON (B) FUEL OFF (1) Shaft (3) Clamp (7) Lever assembly (8) Synchronization screw (9) Rack (11) Unit injector | |
The rack control linkage connects the governor output to unit injector (11) at each cylinder. The governor output shaft is pinned to link (5). The link is connected to lever assembly (4). When the governor demands more fuel, link (5) and lever assembly (4) cause rotation of shaft (1) and clamps (3). Shaft (1) and clamps (3) are rotated in a FUEL ON (A) direction. Each clamp then pushes lever assembly (7) as the shaft rotates. Rack (9) is pulled by lever assembly (7). This will allow more fuel to be injected into the cylinder.
When the governor requires less fuel, link (5) causes rotation of shaft (1) and clamps (3). Shaft (1) and clamps (3) are rotated in a FUEL OFF (B) direction. Lever assembly (7) is forced to rotate clockwise by torsion spring (2). This will push rack (9) toward the shutoff position. A torsion spring is located at each unit injector. This allows the rack control linkage to go to the shutoff position, even if one fuel injector rack is stuck open.
The power setting of the unit injector for the No. 1 cylinder is made with fuel setting screw (6) in clamp assembly (10). As fuel setting screw (6) is turned, shaft (1) rotates to a new position with respect to link (5) and lever assembly (4). Adjusting screws (8) allow synchronization of the injectors to the unit injector of the No. 1 cylinder.
Governor
The governor transfers the operator's requirements to the fuel injector rack control linkage. The governor receives the desired engine speed by the position of the throttle. The governor output shaft immediately moves when the throttle is moved. The motion of the governor output shaft will cause the fuel injector rack control linkage to rotate. This will move the fuel injector racks. The change in the position of the fuel injector rack will cause a change in the speed of the engine. As the speed of the engine changes, the governor will adjust the amount of fuel that is delivered. This will cause the engine to stabilize at the rpm that corresponds to the throttle position. For further information, refer to Service Manual, SENR6454, " 3114, 3116, and 3126 Engine Governors (MUI)".
Fuel Ratio Control
The turbocharged engine uses a fuel ratio control (FRC) in order to control smoke during acceleration at low boost levels. The FRC restricts the amount of fuel to the combustion chambers until sufficient boost has been achieved.
 | |
| Illustration 13 | g00691999 |
Governor linkage and fuel ratio control schematic (A) FUEL ON output (B) FUEL ON input from operator (1) Governor output shaft (2) Inlet port (3) Fuel ratio control (FRC) (4) Retainer shaft (5) FRC lever (6) Limit lever setscrew (7) FRC lever setscrew (8) Limit lever | |
Fuel ratio control (FRC) (3) operates on boost air pressure that is delivered by a tube from the inlet manifold of the engine to inlet port (2). At low boost, retainer shaft (4) is held stationary by springs that are inside the FRC. When the operator demands more fuel, governor output shaft (1) moves in the FUEL ON direction (A). The governor output shaft will move in this direction until limit lever (8) contacts setscrew (7) of FRC lever (5). When FRC lever (5) is restrained from rotating clockwise or FUEL ON movement by the FRC, further FUEL ON movement of governor output shaft (1) is stopped. Thus, overfueling is prevented.
As engine power increases, boost pressure also increases. This pressure acts against a diaphragm inside the FRC. When boost pressure is sufficient, spring force inside the FRC is overcome and retainer shaft (4) moves to the right. This movement will allow FRC lever (5) and limit lever (8) to rotate clockwise. Governor output shaft (1) is now able to move in the FUEL ON direction until the limit lever (8) contacts limit lever setscrew (6) .
When boost pressure decreases, springs inside fuel ratio control (FRC) (3) will return retainer shaft (4) to the normal position. FUEL ON movement of governor output shaft (1) is again restricted.
Fuel Shutoff Solenoid
 | |
| Illustration 14 | g00825990 |
Fuel shutoff solenoid (latching type) (1) Button (2) Fuel shutoff solenoid | |
The fuel shutoff mechanism is activated by a solenoid. This solenoid is a latching type that is energized to run (ETR). A spring loaded plunger inside the solenoid acts on a lever assembly within the front housing of the governor. This lever assembly pushes the governor output shaft to the position of FUEL OFF when the plunger is released electrically or the plunger is released manually at engine shutdown. At engine start-up, the solenoid is energized in order to latch in the run position. The governor output shaft is then free to move to the position of FUEL ON.
Engines that are equipped with solenoids that are a latching type can be manually shut off by pushing button (1) inward. The solenoid CANNOT be manually latched in the run position in order to start the engine.
 | |
| Illustration 15 | g00825197 |
Wiring diagram for the fuel shutoff solenoid (2) Fuel shutoff solenoid (3) "STOP" Connection (4) "G" Connection (5) "S" Connection (6) "BAT" Connection (7) Positive terminal (8) Negative terminal (9) "GND" Connection (10) "START" Connection (11) "MTR" Connection (12) Starter motor (13) Battery | |
Road Speed Limiter (If Equipped)
Road speed limiters are supplied by the vehicle manufacturer or at the request of the vehicle manufacturer. Information on operation, maintenance, diagnostics, and parts should be obtained from the vehicle manufacturer.