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