Ford F150 Pickup. Instruction - part 1614

CATALYST & EXHAUST SYSTEMS

EMISSION SYSTEMS & SUB-SYSTEMS 

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

SELF-DIAGNOSTIC SYSTEMS 

MALFUNCTION INDICATOR LIGHT 

Alternative fuel diagnostics are automatic, active and continuous monitors of the bi-fuel system while the 
vehicle is operating in Compressed Natural Gas (CNG) mode. The system monitors the activity of various 
sensor 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) and the ALT fuel selector switch indicator will change from a 
steady on to an irregular flashing condition. If the fault condition stops, the MIL will return to normal status 
after three trips and the fault code is stored in continuous memory for access during diagnostic procedures. If 
the fault condition does not occur for forty trips, the fault code is erased. 

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. 

TRANSMISSION 

Electronically Controlled Transmission & Torque Converter Clutch 

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/CNG 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/CNG

  

See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

 

2003 Ford Pickup F150 

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

  

2003 ENGINE PERFORMANCE

Theory & Operation - Bi-Fuel - Gasoline/LPG 

INTRODUCTION 

This article covers basic description and operation of bi-fuel engine performance-related systems and 
components. Bi-fuel refers to the F150 Pickup 5.4L that can operate using gasoline or Liquefied Petroleum Gas 
(LPG). Bi-fuel systems are separate and have unique components. Alternative fuels are not compatible and 
should not be mixed or substituted. For illustrations of bi-fuel system components, see Fig. 1 . Read entire 
article before diagnosing vehicles or systems with which you are not completely familiar. 

Switching vehicle operation between gasoline and LPG is performed using ALT/GAS fuel switch inside vehicle 
before ignition is turned on. If vehicle runs out of alternative fuel, system will automatically switch to gasoline 
operation. 

Fig. 1: Identifying Bi-Fuel Liquefied Petroleum Gas System Components 
Courtesy of FORD MOTOR CO. 

COMPUTERIZED ENGINE CONTROLS 

ALTERNATIVE FUEL CONTROL MODULE 

NOTE:

Liquefied petroleum gas may also be referred to as propane. Propane is heavier 
than air.

NOTE:

The Alternative Fuel Control Module (AFCM) is part of the compuvalve 

 

2003 Ford Pickup F150 

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

  

 

2003 Ford Pickup F150 

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

  

AFCM allows communication between compuvalve components and PCM. AFCM communicates desired ALT 
or GAS operating mode to PCM. AFCM shares information with PCM and assists in trouble shooting the bi-
fuel system. If operating conditions are satisfactory and ALT/GAS fuel switch on dash is in ALT mode 
position, the compuvalve will signal PCM to turn gasoline fuel injectors off. If operating vehicle in ALT mode 
and alternative fuel source drops below a specified amount, AFCM will signal PCM to turn gasoline fuel 
injectors on. When this occurs, compuvalve will shut off alternative fuel supply, allowing alternative fuel and 
gasoline fuel systems to switch smoothly. 

COMPUVALVE 

The compuvalve consists of a metering valve assembly, sensors and AFCM. Compuvalve meters fuel 
electronically according to engine load and calculates spark advance for driveability and emissions. 
Compuvalve uses signals from several input devices and also controls output signals to various actuators. See 
INPUT DEVICES and OUTPUT SIGNALS . Input sensors are used to monitor engine performance and 
signal compuvalve to select correct combination of injectors to deliver alternative fuel flow and also alternative 
fuel mass. Correct alternative fuel mass is delivered through a low pressure hose, into fuel rails and injector 
sleeves. Compuvalve calculates alternative fuel mass every spark event. 

Compuvalve also incorporates a Fuel Absolute Pressure (FAP) sensor, Fuel Rail Temperature (FRT) sensor and 
a Manifold Absolute Pressure (MAP) sensor. When in ALT fuel mode, compuvalve will substitute gasoline fuel 
gauge level signal with a signal from fuel level float sensor, located in Liquefied Petroleum Gas (LPG) fuel 
tank. This allows compuvalve to send a LPG fuel level signal to gasoline fuel gauge. 

POWERTRAIN CONTROL MODULE 

Powertrain Control Module (PCM) on bi-fuel models operates just as it would on gasoline models. When 
vehicle is operated in gasoline mode, PCM monitors engine operating conditions by input received from engine 
sensors and AFCM. Control of output actuators determines fuel mixture and idle speed. PCM is located on right 
rear of engine compartment. 

The engine control system consists of PCM, relays, modules, sensors, switches and actuators. PCM sends out 
electrical reference signals to engine sensors and then analyzes input signals. Engine sensors supply PCM with 
specific information, in the form of electrical signals, to determine engine operating conditions. 

PCM uses a memory integrated circuit chip which stores information for Keep Alive Memory (KAM). KAM 
stores memory of vehicle operating conditions and then uses this information for adaptive learning strategy. 
KAM remains powered with ignition off so that input and output information is not lost. 

In the event that one or more input sensors fail, PCM initiates an alternate strategy called Failure Mode Effects 
Management (FMEM) to allow vehicle to maintain driveability. In the event of PCM failure, Hardware Limited 
Operation Strategy (HLOS) will be activated. HLOS is a system of alternate circuitry that provides minimal 
engine operation if PCM fails. During HLOS, all self-test function will stop and system will be controlled by 
electronic hardware. 

Malfunction Indicator Light (MIL) will remain on whenever FMEM or HLOS is in operation. FMEM and 

assembly. See COMPUVALVE .

 

2003 Ford Pickup F150 

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