Ford F150 Pickup. Instruction - part 1616

Vaporizer 

Liquefied Petroleum Gas (LPG) enters vaporizer and is heated to a gaseous state. The gaseous fuel is released to 
compuvalve at 40 psi (276 kPa) when engine coolant temperature is 77°F (25°C) or more. LPG vaporization 
capacity is optimized by dropping fuel delivery pressure when engine coolant temperature is less than 77°F (25°
C). LPG delivery pressure decreases to a minimum of 32 psi (220 kPa) at 32°F (0°C). 

FUEL CONTROL 

For additional information, see LIQUEFIED PETROLEUM GAS SYSTEM . 

Bi-Fuel Relay Module 

The bi-fuel relay module contains 2 replaceable fuses. Fuse No. 1 (3-amp) protects battery feed (BATT) to 
compuvalve. Fuse No. 2 (10-amp) protects BATT feed to bi-fuel power relay which protects VPWR circuits of 
compuvalve. 

Bi-fuel relay module also contains 2 mini ISO relays: the bi-fuel power relay and fuel pump cutoff relay. Bi-
fuel power relay provides power to compuvalve when ignition is on. When ALT/GAS fuel switch is placed in 
ALT position, fuel pump cutoff relay interrupts power from gasoline fuel pump relay to gasoline fuel pump. 

Fuel Injectors & Injector Sleeves 

When in ALT mode, compuvalve sends a signal to PCM to turn off gasoline fuel injectors and gasoline fuel 
pump through bi-fuel relay module. Compuvalve houses 2 types of injectors. The metal-cased injectors are 
"high flow" and deliver fuel during cruise and acceleration and are ON/OFF devices only. The plastic-cased 
injectors are considered as "low flow" injectors. They provide idle and trimming flow and are pulse-width 
modulated as required. 

Fuel flows from compuvalve to adjustable tuning "T", then to fuel rails. Fuel is delivered from fuel rails to 
intake manifold through fuel injector sleeves. Fuel injector sleeves are placed in injector seats. Gasoline fuel 
injectors are placed in fuel injector sleeve seats. The sleeves by-pass gasoline fuel injectors, delivering 
alternative fuel into intake system. 

Lockoff Solenoid Valve 

The lockoff solenoid valve receives VPWR from Inertia Fuel Shutoff (IFS) switch. If IFS is tripped for any 
reason (i.e. accident), or if ignition switch is turned on and there is no tach speed signal received by PCM, 
lockoff solenoid valve will be closed. 

If ALT fuel system automatically switches to GAS mode, lockoff solenoid valve will close. This is triggered 
when Fuel Rail Pressure Sensor (FRPREAB) PID drops to 24.6 psi (170 kPa). Lockoff solenoid valve is located 
near vaporizer and regulates fuel flow into vaporizer inlet. 

IDLE SPEED 

For additional information, see IDLE CONTROL SYSTEM under IDLE SPEED in THEORY & 

 

2003 Ford Pickup F150 

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

  

OPERATION - CNG, FLEX-FUEL & GASOLINE article.

IGNITION SYSTEMS 

Liquefied Petroleum Gas (LPG) fuel burns slower than gasoline under normal operating conditions. The 
compuvalve sends a signal to PCM to advance base vehicle spark timing by 0-15 degrees to improve 
driveability and emissions of vehicle. PCM may or may not advance spark timing at idle depending on 
calibration. For additional information, see IGNITION SYSTEMS in THEORY & OPERATION - CNG, 
FLEX-FUEL & GASOLINE article. 

Bi-fuel systems operating in alternative fuel mode (LPG) are gaseous-type fuel systems that require a higher 
spark plug firing voltage to ignite fuel and puts a higher load on vehicle ignition system. A secondary ignition 
system may not operate well or may exhibit problems when running on alternative fuel; such as backfiring or 
stalling, even though no problems exist while running on gasoline. 

CATALYST & EXHAUST SYSTEMS 

HEATED OXYGEN SENSORS 

The compuvalve monitors upstream Heated Oxygen Sensors (HO2S). The upstream HO2S is used to control 
engine fuel flow. The sensor detects concentration of oxygen in exhaust gas and sends a signal to PCM and to 
compuvalve. In a rich condition, HO2S will output a voltage of 0.6 volt or more, and in a lean condition a 
voltage of 0.4 volt or less will be output. In the event that HO2S fails, Malfunction Indicator Light (MIL) will 
be illuminated. 

EMISSION SYSTEMS & SUB-SYSTEMS 

Since bi-fuel vehicles can operate on gasoline, they have the same emissions equipment as gasoline fueled 
vehicles. See EVAPORATIVE EMISSION SYSTEMS in THEORY & OPERATION - CNG, FLEX-FUEL 
& GASOLINE article. 

SELF-DIAGNOSTIC SYSTEMS 

MALFUNCTION INDICATOR LIGHT 

NOTE:

Since bi-fuel vehicles can operate on gasoline, they have the same catalyst and 
exhaust equipment as gasoline fueled vehicles. For additional information not 
contained in this article, see CATALYST & EXHAUST SYSTEMS in THEORY & 
OPERATION - CNG, FLEX-FUEL & GASOLINE article.

NOTE:

Both gasoline and bi-fuel systems have self-diagnostic capabilities. For 
information on procedures for entering self-test modes and reading DTCs, see 
SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE or SELF-DIAGNOSTICS - 
BI-FUEL - GASOLINE/LPG article.

 

2003 Ford Pickup F150 

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

  

Alternative fuel diagnostics are automatic, active, and continuous monitors of the bi-fuel system when the 
vehicle is operating in Liquefied Petroleum Gas (LPG) mode. The system monitors the activity of system inputs 
and compares the values to calibrated reference criteria. If a signal does not satisfy the reference criteria, a fault 
code is generated and stored. If the fault is of an emissions-critical nature, the system will illuminate the 
Malfunction Indicator Lamp (MIL). Additionally, the selector switch light will change from a steady on to an 
irregular flashing condition. If the fault condition stops, the MIL will return to normal status after 2 trips and the 
fault code is stored for access during diagnostic procedures. See TRIP DESCRIPTION . If the fault condition 
does not occur for forty trips, the fault code is erased. If a temperature-related fault occurs, the compuvalve will 
operate using a default value to protect the engine from severe over or under fueling. The compuvalve will 
continue to use the default value until the next key off/ key on cycle. For additional information, see SELF-
DIAGNOSTICS - BI-FUEL - GASOLINE/LPG article. 

Trip Description 

A "trip" is defined as a Key-On/Key-Off (KOEO) event in which the PCM detects the following:  

z

Engine coolant should be more than 160°F (71°C).  

z

Engine coolant temperature should change more than 40°F (22°C) after starting engine.  

z

Engine speed should be more than 400 RPM.  

z

Vehicle speed should go more than 3 MPH.  

When the AFCM detects an emission related DTC it uses the trip information to make its decision on whether 
to illuminate the MIL light. If a fault exists in the system being tested, a Diagnostic Trouble Code (DTC) will 
be stored in the AFCM memory. Depending on the type of fault detected, some DTCs will command the 
Malfunction Indicator Light (MIL) to illuminate immediately. Other faults will cause the AFCM to store the 
DTC in memory but will not illuminate the MIL until the fault is detected again on a subsequent trip (2nd trip). 

MISCELLANEOUS CONTROLS 

A/C SYSTEM 

A/C Cycling Switch, A/C Evaporator Temperature Sensor, A/C High Pressure Switch & A/C Pressure Sensor 

For additional information, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS in 
THEORY & OPERATION - CNG, FLEX-FUEL & GASOLINE article. 

COOLING FAN 

Cooling Fan Control Relay & Cooling Fan Motor 

For additional information, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS in 
THEORY & OPERATION - CNG, FLEX-FUEL & GASOLINE article.

NOTE:

Although not considered true engine performance-related systems, some 
controlled devices may affect driveability if they malfunction.

 

2003 Ford Pickup F150 

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

  

TRANSMISSION 

Electronically Controlled Transmission & Torque Converter Clutch 

See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

 

2003 Ford Pickup F150 

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