Ford F150 Pickup. Manual - part 1638

Fig. 56: Identifying Variable Cam Timing Solenoid Valve 
Courtesy of FORD MOTOR CO. 

Variable Cam Timing Unit Assembly 

 

2003 Ford Pickup F150 

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

  

Variable Cam Timing (VCT) unit assembly is coupled to camshaft through a helical spline in the VCT unit 
chamber. See Fig. 57 . When flow of oil is shifted from one side of the chamber to the other, differential change 
in oil pressure forces piston to move linearly along the axis of the camshaft. This linear motion is translated into 
rotational camshaft motion through the helical spline coupling. A spring installed in the chamber is designed to 
hold camshaft in minimum overlap position (5 degrees) when oil pressure is too low to maintain adequate 
position control. Camshaft is allowed to rotate up to 30 degrees.

 

2003 Ford Pickup F150 

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

  

Fig. 57: Identifying Variable Cam Timing Unit Assembly 
Courtesy of FORD MOTOR CO. 

CATALYST & EXHAUST SYSTEMS

 

2003 Ford Pickup F150 

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

  

CATALYST SYSTEM 

The catalytic converter and exhaust systems work together to control the release of harmful engine exhaust 
emissions into the atmosphere. Engine exhaust gas consists mainly of Nitrogen (N), Carbon Dioxide (CO2) and 
water vapor (H2O). However, it also contains Carbon Monoxide (CO), Oxides of Nitrogen (NOX), Hydrogen 
(H), and various unburned Hydrocarbons (HCs). CO, NOX, and HCs are major air pollutants, and their 
emission into the atmosphere must be controlled. The exhaust system generally consists of an exhaust manifold, 
front exhaust pipe, upstream Heated Oxygen Sensor (HO2S), rear exhaust pipe, downstream HO2S, a muffler 
and an exhaust tailpipe. The catalytic converter is installed between front and rear exhaust pipes. Catalytic 
converter efficiency is monitored by the OBD-II system. For additional OBD-II Monitor information, see 
DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS. 

The number of HO2S(s) used in the exhaust stream and the location of these sensors depend on the vehicle 
emission certification level (i.e. LEV, ULEV, PZEV). See Fig. 58 and Fig. 59 . On most vehicles, only two 
HO2S are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst will be used for 
primary fuel control while the ones after the catalyst (HO2S12/HO2S22) will be utilized to monitor catalyst 
efficiency. However, some Partial Zero Emission Vehicles (PZEV) will utilize three HO2S sensors for each 
engine bank. The stream 1 sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control, 
the next group of sensors or stream 2 (HO2S12/HO2S22) is utilized to monitor the light-off catalyst and the last 
group of sensors or stream 3 (HO2S13/HO2S23) is utilized for long term fuel trim control to optimize catalyst 
efficiency (Fore Aft Oxygen Sensor Control). Currently Ford's PZEV vehicles use only a 4-cylinder engine, so 
only the Bank 1 HO2S(s) will be utilized. See Fig. 58 and Fig. 59 . 

Fig. 58: Identifying HO2S Locations (V-Engines) 
Courtesy of FORD MOTOR CO. 

 

2003 Ford Pickup F150 

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