Fuel System

1998 Econoline Models
Fuel is drawn from the fuel tank through the primary filter by the diaphragm section of the tandem fuel pump. Pressurized fuel (approximately 28 kPa (4 psi) is supplied to the secondary filter and returned to the second stage of the tandem fuel pump. The piston-actuated second stage of the tandem fuel pump supplies 276-483 kPa (40-70 psi) of fuel to the rear of each cylinder head where it flows to a fuel rail machined in each cylinder head.

Drillings in the cylinder head route the fuel to the plunger area of the fuel injector which can pressurize the fuel to 124 MPa (18,000 psi) for delivery to the combustion chamber via a conventional nozzle/valve tip arrangement.

Return fuel is plumbed from fittings at the front of each cylinder head to a regulator block which contains a piston/spring type regulator valve that maintains pressure to approximately 345 kPa (50 psi). A de-aeration bleed orifice between the fuel filter and the regulator block vents air trapped in the fuel filter. Most of the fuel from the regulator is recirculated to the inlet of the piston (high pressure) stage of the transfer pump. Fuel return to the tank is limited by the fuel filter bleed orifice and a 0.0008 mm (0.020-inch) fuel return bleed orifice. This prevents the fuel from overheating in the tank. A diaphragm accumulator is included.

This system is controlled by the PCM and is composed of the unit injectors, the high pressure oil system, the Injection Driver Module, and the fuel supply system.





1998.5 Econoline Models (with Electric Fuel Pump) and 1999 F-Series
Fuel is drawn from the fuel tank through the primary filter (the screen on the fuel tank sending unit) by the electric fuel pump. Pressurized fuel (approximately 276-552 kPa [40-80 psi]) is supplied to the secondary filter (the fuel filter housing located in the "V" on top of the engine) by means of the electric pump and regulator valve. The regulator relieves the pressure, sending fuel back to the fuel tank. Only the filtered fuel going through the fuel filter will go to the heads. A check valve is located on both heads to prevent fuel pressure spikes in the fuel rail.





Unit Injector
The unit injector is composed of five major components: The electronic solenoid, the poppet valve, the amplifier piston, the fuel plunger, and the nozzle assembly.





High Pressure Oil System
The 7.3L Powerstroke diesel injectors are powered by lubricating oil which is pressurized by a special swashplate pump (Rexroth pump) in the engine valley. The pump output pressure ranges from 3,102 to 20,685 kPa (450 psi to 3,000 psi). This oil pressure is controlled by the Powertrain Control Module (PCM) with a spill valve called the Injector Pressure Regulator. The high pressure oil is delivered to oil rails in the cylinder heads. An injection control pressure sensor mounted on one of the oil rails sends an analog voltage signal (0.5V to 5.0V) to the PCM for feedback control of the oil pressure.

Unit Injector Amplifier Piston
The high pressure oil flows from the oil rails into an amplifier piston located in the injector. Oil entry and exit to and from the amplifier piston is controlled by a solenoid-operated poppet valve.

Unit Injector Fuel Plunger
The fuel plunger is located in the injector and is driven by the amplifier piston. The fuel plunger injects fuel into the combustion chamber at pressures of up to 144,795 kPa (21,000 psi) through the nozzle assembly. Fuel is supplied to the fuel at approximately 483 kPa (70 psi) through fuel rails in the cylinder heads.

Injection Driver Module
The solenoid-operated poppet valve requires 115 volts at up to 8 amps to operate, which is more power than the PCM can supply. Therefore, a high power device, the Injection Driver Module, is used to supply power to the solenoid on command from the PCM.

PCM Control of Fuel Injection
The command signal from the PCM to the Injection Driver Module is the Fuel Delivery Control Signal. The poppet requires 12 volts to command the poppet open and 0 volts to command the poppet closed. The PCM also supplies a synchronizing signal, CMP, to indicate cylinder No. 1 (going from 0 to 12 volts) and cylinder No. 4 (fires 5th) (going from 12 to 0 volts).

Engine Timing
The PCM controls both duration and timing of the injection event with the fuel delivery control signal. Signal duration, or fuel pulse width, is shown as Parameter ID (PID) "FUEL__PW" on the New Generation Star (NGS) Tester 007-00500.

The PCM controls the fuel plunger injection pressure and fuel volume by varying the injection oil pressure with the Injection Pressure Regulator. The command to the Injection Pressure Regulator is a 12 volt, Pulse Width Modulated (PWM) signal (controlled on the ground side).

The injection oil pressure command is shown as NGS PID IPR which is the percentage ON of the pulse width modulated signal. Injection oil pressure is shown as NGS PID ICP

The PCM receives engine rotational position information from the Camshaft Position sensor (CMP). The CMP is a hall-effect device. It outputs 12 volts to the PCM whenever it detects the iron of a spoked target wheel in front of it, and it outputs 0 volts whenever it detects the space between the spokes. The target wheel spokes and spaces are each 15 crank degrees, except for narrow spoke which indicates cylinder No. 1 and a wide spoke which indicates cylinder No. 4 (fires 5th). The NGS PID RPM is generated by the PCM from the CMP signal.

Fueling Corrections
The PCM adjusts injector output based on oil temperature information received from the engine oil temperature sensor and turbo boost information received from the Manifold Absolute Pressure (MAP) Sensor, and the Barometric pressure (BARO) sensor. These corrections are necessary to meet emissions requirements and to optimize power Outputs of these sensors are displayed on the NGS tester as EOT (temperature), MAP (pressure), MAP H (sensor frequency), BARO (pressure), and BARO V (volts). MGP shows boost, which is MAP minus BARO pressure.