Fuel System
FUEL SYSTEMThe alternative fuel system consists of Liquefied Petroleum Gas (LPG) fuel tanks, a fuel filter, an LPG vaporizer/regulator, a combined metering valve and sensor assembly called a compuvalve, fuel shutoff solenoids, an Alternative Fuel Control Module (AFCM), a factory set adjustable tuning tee, fuel rails, fuel injector sleeves, an ALT/GAS switch, an ALT/GAS switch light, and an ALT fuse/relay module.
Liquefied Petroleum Gas (LPG) System
Liquid propane from the liquefied petroleum gas (LPG) fuel tank flows through the manual shutoff valve through the fuel filter to the lock-oft solenoid, located either before, or in the vaporizer. When the lock-oft solenoid is open, liquid propane flows into the vaporizer heat exchanger. Heat from the engine coolant is used to convert the liquid fuel to gas. When engine coolant is below 0°C (32°F), a cold start heater is used to provide heat to the heat exchanger of the vaporizer. The vaporizer provides gaseous propane at a consistent operating pressure to the compuvalve. The compuvalve meters fuel according to demand and calculates spark advance for maximum power and driveability. A combination of sensors and inputs from the Powertrain Control Module (PCM) are used to monitor the engine and the environment to provide closed loop control of fuel. The compuvalve directs fuel through the low pressure hose to a factory set adjustable tuning tee, through the fuel rail assemblies and is introduced into the intake system through fuel injector sleeve assemblies.
Bi-Fuel Switch-Over Pressures and Temperatures
Bi-Fuel Switch-Over Pressures and Temperatures Chart:
If engine operating temperature is excessively cold, LPG operation may be delayed until fuel temperature at the vaporizer reaches a sufficiently high level to permit consistent operation fuel pressure.
Alternative Fuel Tank
The LPG fuel tanks are refillable storage tanks requiring replacement only when damaged or upon failing an inspection. The LPG tank is welded steel construction. The LPG tanks are refueled through the use of a fuel fill valve (located behind the fuel filler door) containing a safety valve that only allows one-way fuel flow to the tanks. The LPG fuel tanks are connected to the fill valve by a high-pressure hose.
The F-150 is supplied with either single or dual tank configurations, which are bolted inside the forward area of the bed floor.
The LPG dual tank configuration uses hollow support tubes welded to both tanks that also serve as crossover tubes.
The LPG fuel tank is fitted with an 80% outage valve (used when refueling), an 80% auto stop/till valve and an internal float device used to monitor the fuel level.
Fuel Filter
The fuel filter removes particulate contamination from the LPG fuel system. LPG fuel travels through this filter in a liquid state.
Fuel Injector Valves
When in LPG mode, the compuvalve instructs the powertrain control module (PCM) to shut oft the gasoline fuel injectors and the gasoline fuel pump through the ALT fuse/relay module. The compuvalve houses two types of injectors. The metal cased injectors are "high flow" and deliver fuel during cruise and acceleration. These are strictly on/oft devices. The plastic-cased injectors provide idle and trimming flow. These "low flow" injectors are pulse-width modulated as required. The fuel is delivered to the intake manifold via fuel injector sleeves.
Vaporizer
Liquid propane enters the vaporizer and is then heated to a gaseous state. The gaseous fuel is released to the compuvalve at 40 psia for engine coolant temperatures greater than or equal to 25°C (77°F). Below this temperature, delivery pressure decreases with reduction of engine coolant temperature to a minimum of 32 psia at 0°C (32°F), optimizing vaporization capacity.
ALT Fuse/Relay Module
The ALT fuse/relay module contains two replaceable fuses. Refer to the Vehicle/Diagrams for fuse location. Fuse 1 (3A) protects the Battery feed (BATT) to the compuvalve and Fuse 2 (10A) protects the BATT to the ALT fuel power relay, in turn protecting the VPWR circuits of the compuvalve. The ALT fuse/relay module also contains two dual mini ISO relays: the ALT fuel power relay and the fuel pump cutoff relay. The ALT fuel power relay provides power to the compuvalve when the key is in the ON position. The fuel pump cutoff relay interrupts the power to the gasoline fuel pump from the base gasoline fuel pump relay when the ALT/GAS switch is placed in the ALT position.
Alternative Fuel Control Module (AFCM)
The Alternative Fuel Control Module (AFCM) is incorporated within the compuvalve and allows communication between the compuvalve and the powertrain control module (PCM). The AFCM communicates desired operating mode, ALT or GAS, to the PCM. This allows information to be shared between modules and facilitates troubleshooting. When ALT mode is selected and operating conditions are satisfactory, the compuvalve, through the AFCM, signals the PCM to turn off the gasoline fuel injectors. During alternative fuel operation, if the fuel source drops below a specified amount, the compuvalve through the AFCM signals the PCM to turn on the gasoline fuel injectors while the compuvalve shuts off alternative fuel. This allows smooth switching of fuel systems.
Solenoid Lockoff Valve
The solenoid lockoff valve receives VPWR from the Inertia Fuel Shutoff (IFS) switch. If the IFS is tripped for any reason (i.e. accident), or if the key is on and there is no tach signal received, the solenoid lockoff valve will be closed. The solenoid lockoff valve is positioned close to the vaporizer and controls fuel flow into the vaporizer inlet.
In the event that the ALT fuel system auto switches to base gasoline mode, the solenoid lockoff valve will close. This is triggered when the FRPREAB PID drops to 25 psia.
Compuvalve
The compuvalve electronically meters fuel according to demand and calculates additional spark advance for optimum driveability and emissions. A combination of sensors and inputs are used to dynamically monitor the engine operating environment. Fuel is delivered through the low pressure hose into the fuel rails and through the injector sleeves. Internal to the compuvalve are the Fuel Absolute Pressure (FAP) sensor, the Fuel Rail Temperature (FRT) sensor, the Manifold Absolute Pressure (MAP) sensor, and the Alternative Fuel Control Module (AFCM). The compuvalve communicates to the instrument cluster (on the SCP lines) a signal from a float-style sensor in the alternative fuel tank. This allows the compuvalve to display the alternative fuel level on the gasoline fuel gauge while in ALT mode.
Fuel Level Float
A float-style fuel level sending unit is mounted in the alternative fuel tank. The compuvalve receives input from the fuel level float and sends a signal to the base gasoline fuel gauge representing the level of liquid propane.
Cold Start Heater
The cold start heater is integral to the vaporizer/regulator. When engine coolant is below 0°C (32°F) the cold start heater turns on and turns oft when engine coolant reaches 10°C (50°F). The cold start heater is used to provide heat to the heat exchanger in the vaporizer.
Cold Start Heater Relay
The cold start heater is controlled by the compuvalve via the cold start relay.
ALT/GAS Switch, ALT/GAS Switch Light
The ALT/GAS switch permits the driver to select which fuel the vehicle will operate on. The ALT/GAS switch is located on the instrument panel.
The ALT/GAS switch only operates when the vehicle is at a stop with the ignition in the OFF position. If the switch is moved while the vehicle is running, the gaseous fuel system will NOT automatically change fuel mode and no damage to the vehicle will occur.
Prior to starting the vehicle (with the ignition in the OFF position), determine which fuel you intend to use and press the ALT/GAS switch.
When the selector switch is placed in the GAS position, the engine will operate in the unleaded gasoline mode.
When the switch is placed in the ALT position the engine will operate in the gaseous fuel mode (it temperature and pressure conditions are correct), running on LPG. A green indicator light will illuminate on the fuel selector switch to indicate that the vehicle is operating in the gaseous fuel mode.
The ALT/GAS switch sends a signal to the compuvalve requesting ALT fuel mode, when placed in the ALT position. If no signal is received by the compuvalve, the system defaults to base gasoline mode. The ALT/GAS switch light is incorporated into the ALT/GAS switch. It is controlled by the compuvalve and is illuminated when operating in ALT/FUEL mode. If an emission-critical Diagnostic Trouble Code (DTC) is recorded, the ALT/GAS switch light will change from a steady on to an irregular flashing condition. If a communication fault arises the indicator will flash with a steady pulse. Once the key is switched to ON, the switch will not change the fuel operating mode. The ALT/GAS switch light has the following status modes:
- OFF
- ON STEADY
- ON THEN OFF (Quickly or Slowly)
- FLASHING (REGULAR OR IRREGULAR)
Fuel Gauge
Fuel gauge operation in an LPG Bi- Fuel vehicle behaves similarly to a standard gasoline fuel gauge. The fuel gauge provides a linear reading from full down to empty. Fuel gauge operation is based on a float type sensor measuring the level of the LPG in the fuel tanks.
F-Series vehicles have their instrument cluster connected to the SCP bus (BUS+ and BUS-). Intercepts are not required in the fuel gauge and instrument cluster power signals because the Bi-Fuel system can send fuel level data over the SCP bus. Refer to the Vehicle/Diagrams for information about Bi- Fuel system electrical taps and intercepts.
Adjustable Tuning Tee
The adjustable tuning tee allows a proportioned percentage of the fuel flow to each of the fuel rails. There are two individual adjustment screws, one for each of the two output fuel lines. The tuning tee is preset at the factory. No adjustments are necessary unless the tuning tee is replaced.
Fuel Rail
The fuel rails route alternative fuel from the compuvalve to the base vehicle intake runners.
Injector Sleeves
The injector sleeves are placed in the injector seats. The gasoline fuel injectors are placed in the injector sleeve seats. The sleeves bypass the gasoline fuel injectors, delivering alternative fuel into the intake system and providing a path of fuel flow from the gasoline injectors.
Fuel Absolute Pressure Sensor
The fuel absolute pressure (FAP) sensor is integral to the compuvalve. It is a pressure transducer that converts pressure to voltage through a piezo-resistive element. This signal is monitored to make sure that the pressure regulator is functioning properly and is used to adjust the injector combination according to supply pressure. The FAP sensor allows the vehicle to start in ALT fuel mode at a minimum of 25 psia. It also controls when the vehicle will auto switch to gasoline (25 psia).
Fuel Rail Temperature Sensor
The Fuel Rail Temperature (FRT) sensor is integral to the compuvalve. The FRT is used to calculate fuel density. It is supplied five volts from the compuvalve and as the temperature of the sensing element increases, its resistance increases.
Manifold Absolute Pressure Sensor
The manifold absolute pressure (MAP) sensor is integral to the compuvalve. It is a pressure transducer that converts pressure to voltage through a piezo-resistive element. It is attached to the intake manifold via a vacuum line with a damper tube that is routed to an external hose barb on the compuvalve. MAP is used to monitor engine operating state.