Ford F150 Pickup. Instruction

Individual COPs are mounted directly on spark plugs. See Fig. 26 . CKP sensor is used by PCM to indicate
crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted on front of crankshaft. The
CMP sensor is used by PCM to identify when piston No. 1 is at Top Dead Center (TDC) of compression stroke.
This signal is used to synchronize firing of individual coils.

The individual coils receive their signal from PCM to fire at a calculated spark target. Only one coil is fired at a
time and only on compression stroke. PCM acts as an electronic switch to ground individual coil primary
circuit. When the switch is closed, battery voltage applied to coil primary circuit builds a magnetic field around
primary coil. When the switch opens, power is interrupted and primary field collapses, inducing high voltage in
secondary coil winding and spark plug is fired. For additional COP information, see COIL ON PLUG under
OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS.

VARIABLE CAM TIMING SYSTEM

VARIABLE CAM TIMING

Description

There are four possible types of Variable Cam Timing (VCT) systems. The 2003 ZX2 are Exhaust Phase
Shifting (EPS) system. The exhaust cam is the active cam and is being retarded. The 2003 LS, Thunderbird and
Focus SVT vehicles have Intake Phase Shifting (IPS) system. A intake phase shifting system will move the
intake cam in the advance direction. The other two possible systems are Dual Equal Phase Shifting (DEPS) both
intake and exhaust cams are phase shifted equally as well as Dual Independent Phase Shifting (DIPS) where the
cams are shifted independently. The systems have three operational modes; idle, part throttle, wide open throttle
and a default mode. At idle and (low engine speeds with closed throttle) the phase angle is controlled by air
flow and engine coolant temperature. At part and wide open throttle the PCM controls cam timing based on
engine RPM, load, and throttle position. VCT systems provide reduced emissions and enhance engine power,
fuel economy and idle quality. IPS systems have the added benefit of improve torque. In addition a VCT system
will eliminate the need for an external Exhaust Gas Recirculation (EGR) system. The elimination of EGR
system is accomplished by controlling the overlap in valve opening between the intake valve opening and
exhaust valve closing. Increased vehicle reliability is achieved with the elimination of the EGR system.

The VCT system consists of an electric hydraulic positioning control solenoid, a CMP and trigger wheel. The
CMP trigger wheel has a number of equally spaced teeth equal to the number (n) of cylinders on a bank plus
one extra tooth (n+1). Four cylinder and V8 engines use a CMP 4+1 tooth trigger wheel. V6 engines use a CMP
3+1 tooth trigger wheel. The extra tooth placed between the equally spaced teeth represents the CMP signal for
that bank. A CKP provides the PCM with crankshaft positioning information in 10 degree increments.

The following list of components and their specific operation corresponds to numbers in illustration. See Fig.
55 .

1. The PCM receives input signals from the IAT, ECT, CMP, TP, MAF and CKP to determine the operating

conditions of the engine. At idle (low engine speeds and closed throttle) the PCM controls camshaft
position based on air and coolant temperatures. During part and wide open throttle, camshaft position is
determined by engine RPM, load and throttle position. The VCT system will not operate until the engine
is at normal operating temperature.

2. VCT system is enabled by PCM when the proper conditions are met. PCM disables VCT system if a fault

2003 Ford Pickup F150

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

is detected.

3. The CKP signal is used as a reference for CMP positioning.

4. The PCM calculates and determines the desired camshaft position. It will continually update the VCT

solenoid duty cycle until desired positioning is achieved. A difference between the desired and actual
camshaft position represents a position error in the PCM's VCT control loop. The PCM will disable the
VCT and place the camshaft in a default position if a fault is detected.

5. Oil flows to either side of the piston chamber in the VCT assembly, which changes the linear piston

motion to a rotational motion that advances or retards the camshaft.

Fig. 55: Identifying Variable Cam Timing System Components & Circuits
Courtesy of FORD MOTOR CO.

Variable Cam Timing Solenoid Valve

The VCT solenoid valve is an integral part of the VCT system. See Fig. 56 . The solenoid valve controls the
flow of engine oil in the VCT assembly. As the PCM controls the duty cycle of the solenoid valve, oil
pressure/flow advances or retards the cam timing. Duty cycles near 0 or 100 percent represent rapid movement
of the camshaft. Retaining a fixed camshaft position is accomplished by dithering (oscillating) the solenoid
valve duty near 50 percent.

2003 Ford Pickup F150

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

Ford F150 Pickup. Instruction - part 1637