Ford F150 Pickup. Instruction - part 1615

HLOS substitute a fixed signal and continue to monitor system failure. If signal(s) return to within operating 
limits, PCM will resume normal operation. 

INPUT DEVICES 

The available input signals for Liquefied Petroleum Gas (LPG) include the following: 

ALT/GAS Fuel Switch 

The ALT/GAS fuel switch allows driver to select which fuel vehicle will operate on. The ALT/GAS fuel switch 
is located on instrument panel and ALT/GAS fuel switch indicator is incorporated into ALT/GAS fuel switch. 
The ALT/GAS fuel switch only operates when vehicle is at a stop with ignition off. Once ignition is turned on, 
ALT/GAS fuel switch will not change fuel operating mode. If switch is moved while vehicle is running, 
gaseous fuel system will not automatically change fuel operating mode and no damage to vehicle will occur. 

With ignition off, prior to starting vehicle, determine which fuel you intend to use and press ALT/GAS fuel 
switch. When selector switch is placed in GAS position, engine will operate in unleaded gasoline mode. When 
switch is placed in ALT position, engine will operate in gaseous fuel mode so long as temperature and pressure 
conditions are correct for operating on LPG. A Green indicator light will illuminate on fuel selector switch to 
indicate that vehicle is operating in gaseous fuel mode (LPG). The ALT/GAS fuel switch sends a signal to 
compuvalve requesting ALT fuel mode, when placed in ALT position. If no signal is received by compuvalve, 
fuel system defaults to base gasoline mode. 

Fuel Level Float Sensor 

Fuel Level Float (FLF) sensor is a float style fuel level sending unit is mounted in Liquefied Petroleum Gas 
(LPG) tank. The Compuvalve receives an input signal from FLF, interrupts the signal from the gasoline tank 
fuel sender and sends a pulse-width modulated signal to instrument cluster fuel gauge representing the level of 
LPG. 

Fuel Absolute Pressure Sensor 

The Fuel Absolute Pressure (FAP) sensor is integral to compuvalve. FAP sensor is a pressure transducer that 
converts pressure to voltage through a piezo-resistive element. FAP voltage signal is monitored to ensure that 
gas regulator is operating correctly. FAP sensor is used to adjust which injector combination is used. FAP 
sensor allows vehicle to start in ALT fuel mode at a minimum of 24.6 psi (170 kPa) for LPG. When LPG 
pressure is at 24.6 psi (170 kPa), FAP sensor sends a signal to AFCM and compuvalve, and bi-fuel system will 
automatically switch from ALT mode to GAS mode. For additional bi-fuel switch over specifications, see Fig. 
2 . 

NOTE:

Only alternative fuel input devices for bi-fuel vehicles are listed in this article. 
For additional information on gasoline input devices for bi-fuel vehicles, see 
INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS in THEORY & 
OPERATION - CNG, FLEX-FUEL & GASOLINE article.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - Bi-Fuel - Gasoline/LPG

  

Fig. 2: Bi-Fuel Switch Over Pressure & Temperature Specifications 
Courtesy of FORD MOTOR CO. 

Fuel Rail Temperature Sensor 

Fuel Rail Temperature (FRT) sensor is integral to compuvalve. FRT sensor is used to calculate fuel density. 
FRT sensor is supplied a 5-volt reference signal from compuvalve and as temperature of fuel sensor element 
increases, FRT sensor resistance increases. 

Manifold Absolute Pressure Sensor 

Manifold Absolute Pressure (MAP) sensor is integral to compuvalve. MAP sensor is a pressure transducer that 
converts pressure to voltage through a piezo-resistive element. A vacuum line with a damper tube is connected 
between compuvalve external hose barb for MAP sensor and intake manifold. MAP sensor is used to monitor 
engine operating state. 

OUTPUT DEVICES 

NOTE:

Only alternative fuel output devices for bi-fuel vehicles are listed in this article. 
For additional information on gasoline-related output devices for bi-fuel 
vehicles, see OUTPUT DEVICES under COMPUTERIZED ENGINE CONTROLS in 
THEORY & OPERATION - CNG, FLEX-FUEL & GASOLINE article.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - Bi-Fuel - Gasoline/LPG

  

ALT/GAS Switch Indicator 

The ALT/GAS fuel switch indicator is controlled by compuvalve and is illuminated when operating in ALT 
fuel mode. If an emission-related DTC is set, ALT/GAS fuel switch indicator will change from a steady on, to 
an irregular flashing condition. If a communication fault exists, indicator will flash with a steady pulse. The 
ALT/GAS fuel switch indicator has the following status modes: OFF, ON steady, ON and then OFF (quickly or 
slowly), and FLASHING (regular or irregular - quickly or slowly). 

Bi-Fuel Relay Module 

See FUEL CONTROL under FUEL SYSTEMS. 

Cold Start Heater 

See FUEL DELIVERY under FUEL SYSTEMS. 

Cold Start Heater Relay 

See FUEL DELIVERY under FUEL SYSTEMS. 

Fuel Injectors 

See FUEL CONTROL under FUEL SYSTEMS. 

Self-Diagnostics 

See SELF-DIAGNOSTIC SYSTEMS . 

Solenoid Lockoff Valve 

See FUEL CONTROL under FUEL SYSTEMS. 

Vaporizer 

See FUEL DELIVERY under FUEL SYSTEMS. 

FUEL SYSTEMS 

The bi-fuel systems consist of Liquefied Petroleum Gas (LPG) fuel tanks, a vaporizer, a combined metering 
valve, sensor and Alternative Fuel Control Module (AFCM) assembly (compuvalve), fuel shutoff solenoids, an 
adjustable tuning "T", fuel rails, fuel injector sleeves, an ALT/GAS fuel switch and ALT/GAS fuel switch 
indicator, and a bi-fuel relay module. 

NOTE:

Vehicles are equipped with different combinations of computer-controlled 
components. Not all components listed below are used on every vehicle. For 
theory and operation on each output component, refer to system indicated after 
component.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - Bi-Fuel - Gasoline/LPG

  

LIQUEFIED PETROLEUM GAS SYSTEM

Liquefied Petroleum Gas (LPG) flows from fuel tank through the instruction shutoff valve, coalescent fuel filter 
and lockoff solenoid, located in the vaporizer. See Fig. 1 . When lockoff solenoid is open, LPG flows into 
vaporizer heat exchanger. Heat from engine coolant is used to aid in converting the LPG to a gaseous state. 
When engine coolant is less than 32°F (0°C), a cold start heater is used to provide heat to heat exchanger. 
Vaporizer provides gaseous fuel at a consistent operating pressure to compuvalve. 

Compuvalve meters fuel according to demand and calculates spark advance for maximum power and 
driveability. A combination of sensors and input signals from PCM are used to monitor engine and operating 
environment to provide closed loop control of LPG. Compuvalve directs LPG through the low pressure hose to 
an adjustable tuning "T", through the fuel rail assemblies and into the intake system through fuel injector sleeve 
assemblies. 

FUEL DELIVERY 

Adjustable Tuning "T" 

The adjustable tuning "T" allows a proportioned percentage of fuel flow to each of the fuel rails. There are 2 
individual adjustment screws, one for each of the 2 output fuel lines. The tuning "T" is preset at factory. No 
adjustments are necessary, unless tuning "T" is replaced. 

Cold Start Heater 

The cold start heater is integral to vaporizer/regulator. Cold start heater turns on when engine coolant is less 
than 32°F (0°C), and turns off when engine coolant reaches 50°F (10°C). Cold start heater is used to provide 
heat to heat exchanger in vaporizer in event engine coolant is not more than 32°F (0°C). 

Cold Start Heater Relay 

Compuvalve signals cold start relay to operate cold start heater when compuvalve receives a signal from PCM 
through SCP BUS(+) or BUS(-) circuits that engine coolant temperature is less than 32°F (0°C). 

Fuel Filter 

The fuel filter removes particulate contamination from LPG fuel system. LPG fuel travels through this filter in a 
liquid state. 

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 to empty. Fuel gauge operation for an LPG bi-fuel vehicle is based on 
a float type sensor measuring the level of liquid propane in the fuel tank(s). On all models, the instrument 
cluster is connected to SCP BUS(+) and BUS(-) circuits.

NOTE:

Liquefied petroleum gas may also be referred to as propane.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - Bi-Fuel - Gasoline/LPG