Ford F150 Pickup. Manual - part 1630

Fig. 31: Identifying Thermostat Heater Control 
Courtesy of FORD MOTOR CO. 

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

During high speed, high load, high temperature conditions (air charge, transmission oil or engine coolant), PCM 
output is energized with a duty cycle to thermostat heater. This heats the wax and forces thermostat to rapidly 
open wider allowing extra coolant to flow from radiator. This will reduce coolant temperature and improve with 
performance demand. The heater is only capable of supplying a small amount of additional heat to wax element. 
It is not capable of opening thermostat alone. The thermostat is 100 percent duty cycle for short calibrated time 
and than duty cycle is reduced to a maximum of 70 percent ON and 30 percent OFF. Unheated, thermostat will 
begin to open at a coolant temperature of about 208°F (98°C), and will be fully open at 226°F (108°C). 
Energizing heater will reduce opening temperature to about 154°F (68°C), and the fully open temperature to 
217°F (103°C). 

Transmission Control Indicator Light 

Transmission Control Indicator Light (TCIL) is an output signal from PCM that controls indicator light on/off 
function depending on engagement or disengagement of overdrive. See TRANSMISSION CONTROL 
SWITCH under INPUT DEVICES. 

Wide Open Throttle A/C Cut-Off Relay 

The WAC relay is normally open (normally closed for Aviator). There is no direct electrical connection 
between A/C switch or Electronic Air Temperature Control (EATC) module and A/C clutch. On some 
applications, A/C request signal will be sent to PCM through Standard Corporate Protocol (SCP) BUS (+) and 
BUS (-) circuits. When A/C is requested, PCM will ensure all other A/C related inputs and engine components 
are operating correctly before grounding WAC relay output (unground for Aviator), causing voltage to be sent 
to A/C clutch. 

Vapor Management Valve 

See FUEL EVAPORATIVE SYSTEM under EVAPORATIVE EMISSION SYSTEMS. 

Vehicle Speed Output 

Powertrain Control Module - Vehicle Speed Output (PCM-VSO) speed signal subsystem generates vehicle 
speed information for vehicle's electrical/electronic modules and subsystems that require vehicle speed data. 
This subsystem senses transmission output shaft speed using a sensor. See OUTPUT SHAFT SPEED 
SENSOR or VEHICLE SPEED SENSOR under INPUT DEVICES. Vehicle speed data is processed by PCM 
and distributed as a hard-wired signal or as a multiplexed data message. 

Key features of PCM-VSO system are to:  

z

Infer Vehicle Movement From Output Shaft Sensor Signal  

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Convert Transmission Output Shaft Rotational Information To Vehicle Speed Information  

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Compensate For Tire Size & Axle Ratio With A Programmed Calibration Variable  

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Utilize Transfer Case Sensor For Four Wheel Drive Applications 

NOTE:

The Wide Open Throttle A/C Cut-Off (WAC) relay may also be referred to as the 
A/C clutch relay.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

z

Distribute Vehicle Speed Information As A Multiplexed Message &/Or An Analog Signal  

The signal from a non-contact shaft sensor mounted on transmission (OSS) or transfer case (TCSS) is sensed 
directly by PCM. PCM converts OSS or TCSS information to 8000 pulses per mile, based on a tire and axle 
ratio conversion factor. This conversion factor is programmed into PCM at time of vehicle assembly and can be 
reprogrammed in the field for servicing changes in tire size and axle ratio. PCM transmits computed vehicle 
speed and distance traveled information to all vehicle speed signal users. 

VSO information can be transmitted by a hard-wired interface between vehicle speed signal user and PCM, or 
by speed and odometer Standard Corporate Protocol (SCP) multiplexed data messages. VSO hard-wired signal 
wave form is a DC square wave with a voltage level of zero to battery voltage. Typical output operating range is 
2.22Hz per MPH. Multiplexed data for speed and distance data are transmitted as separate SCP messages over 
SCP multiplex link. 

Vistronic Drive Fan 

The primary purpose for the Vistronic Drive Fan (VDF) clutch is to optimize fan energy (i.e. improved fuel 
economy) while meeting cooling performance requirements. Successful optimization will also minimize 
objectionable fan noise. The operation is similar to the existing viscous fan clutch, except viscous fluid flow is 
controlled by a Pulse Width Modulated (PWM) solenoid versus a bi-metal temperature sensor on the front of 
the clutch. 

The VDF consists of three main elements, a working chamber, a reservoir chamber, and a Fan Speed Sensor 
(FANSS). A fluid port valve controls fluid flow from the reservoir into the working chamber. Once viscous 
fluid is in the working chamber, "shearing" of the fan clutch fluid will result in fan rotation. The valve is 
activated via a PWM output signal from the PCM. By opening and closing the fluid port valve, the PCM can 
control approximate fan speed. Fan speed is monitored via a Hall Effect sensor and is read by the PCM for 
closed loop operation. 

The PCM will optimize the VDF fan speed based upon CHT, TFT, or IAT cooling requirements. When either 
of these inputs is demanding increased fan speed for vehicle cooling, the PCM will monitor the Hall Effect Fan 
Speed Sensor (FANSS), and output the resultant PWM signal to the fluid port valve thus controlling to the 
required fan speed. 

FUEL SYSTEMS (GASOLINE) 

FUEL DELIVERY 

FUEL SYSTEM IDENTIFICATION 

Application

Fuel System

Blackwood, Econoline, Excursion Navigator, Pickup & Windstar

(1)

 Returnable

Escape, Expedition, Explorer, Explorer Sport, Explorer Sport Trac, 
Mountaineer & Ranger

(2)

 Mechanical 

Returnless

All Others

(3)

Electronic 

Returnless

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

  

There are 3 different types of fuel systems that are used: 

Returnable Fuel System 

Returnable fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter
(s), Schrader/pressure test port, fuel rail, fuel injectors, and fuel pressure regulator. The following list of 
components and their specific operation corresponds to numbers in illustration. See Fig. 32 .  

1. The fuel delivery system uses Crankshaft Position (CKP) sensor to signal PCM that engine is either 

cranking or running.  

2. The fuel pump logic is defined in Fuel System control strategy and is executed in PCM. PCM will ground 

fuel pump relay for one second during Key On Engine Off. During cranking, fuel pump relay is grounded 
as long as PCM receives a CKP signal.  

3. The fuel pump relay has a primary and a secondary circuit. Primary side is controlled by PCM and 

secondary side provides battery voltage (B+) to fuel pump circuit when relay is energized.  

4. The Inertia Fuel Shutoff (IFS) switch is used to de-energize fuel delivery secondary circuit in the event of 

a collision. IFS switch is a safety device that should only be reset after a thorough inspection of the 
vehicle (following a collision). For additional IFS information, see INERTIA FUEL SHUTOFF 
SWITCH (ALL FUEL SYSTEMS) .  

5. The fuel injector is a solenoid operated valve that meters fuel flow to each cylinder. Fuel injector is 

opened and closed a constant number of times per crankshaft revolution. Amount of fuel is controlled by 
length of time fuel injector is held open. Fuel injector is normally closed and is operated by a 12-volt 
VPWR signal from power relay. The ground signal is controlled by PCM. For additional fuel injector 
information, see FUEL INJECTORS under FUEL CONTROL.  

6. A pressure test point valve (Schrader valve) is located on fuel rail. This is used to measure fuel injector 

supply pressure for service and diagnostic procedures. On vehicles not equipped with a Schrader valve, 
use Rotunda Fuel Pressure Test Kit (134-R0087) or equivalent.  

7. The fuel pressure regulator is attached to fuel rail downstream of fuel injectors. It regulates fuel pressure 

supplied to fuel injectors. Fuel pressure regulator is a diaphragm operated relief valve. See Fig. 33 . One 
side of diaphragm senses fuel pressure and the other side is connected to intake manifold vacuum. Fuel 
pressure is established by a spring preload applied to diaphragm. Balancing one side of diaphragm with 
manifold vacuum maintains a constant fuel pressure drop across fuel injectors. Fuel pressure is high when 
engine vacuum is low. Excess fuel is by-passed through fuel pressure regulator and returned through a 
fuel return line to fuel tank.  

8. There are 4 filtering or screening devices in fuel delivery system. Fuel intake sock or screen is a fine, 

nylon mesh mounted on intake side of fuel pump. See Fig. 34 . There is a fuel filter screen located at fuel 
rail side of fuel injector. A fuel filter/screen is located in the inlet side of fuel pressure regulator. The fuel 
filter assembly is located between fuel pump and pressure test point/Schrader valve.  

9. The Fuel Pump (FP) module is a device that contains both fuel pump and fuel sender assembly. The fuel 

(1)

See RETURNABLE FUEL SYSTEM .

(2)

See MECHANICAL RETURNLESS FUEL SYSTEM .

(3)

See ELECTRONIC RETURNLESS FUEL SYSTEM .

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline