Ford F150 Pickup. Manual — part 1639

Fig. 59: Identifying HO2S Locations (In-Line Engines)
Courtesy of FORD MOTOR CO.

Catalytic Converter

A catalyst is a material that remains unchanged when it initiates and increases the speed of a chemical reaction.
A catalyst will also enable a chemical reaction to occur at a lower temperature. The catalytic converter assists in
controlling the concentration of exhaust gas products released to the atmosphere. It contains a catalyst in the
form of a specially treated ceramic honeycomb structure saturated with catalytically active precious metals. As
exhaust gases come in contact with the catalyst, they are changed into mostly harmless products. The catalyst
initiates and speeds up heat producing chemical reactions of the exhaust gas components so they are used up as
much as possible. For additional 3-Way Catalytic (TWC) converter information, see 3-WAY CATALYTIC
CONVERTER .

Light Off Catalyst

As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50
percent is called catalyst light off. For most catalysts this point occurs at 475-575°F (246-301°C). A fast light
catalyst is a 3-Way Catalyst (TWC), that is located as close to exhaust manifold as possible. Because light off
catalyst is located close to exhaust manifold it will light off faster and reduce emissions quicker than the catalyst
located under vehicle. Once catalyst lights off, the catalyst will quickly reach maximum conversion efficiency.

2003 Ford Pickup F150

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

3-Way Catalytic Converter

The 3-way Catalytic (TWC) converter contains either Platinum (Pt) and Rhodium (Rh), or Palladium (Pd) and
Rhodium (Rh). TWC converter catalyzes oxidation reactions of unburned HCs and CO and reduction reaction
of NOx. The 3-way conversion can be best accomplished by always operating engine air fuel/ratio at or close to
stoichiometry (14.7:1). For additional stoichiometry information, see 3-WAY CATALYST CONVERSION
EFFICIENCY .

3-Way Catalyst Conversion Efficiency

A TWC requires a stoichiometric fuel ratio, 14.7 pounds of air to one pound of fuel (14.7:1), for high
conversion efficiency. In order to achieve these high efficiencies, air/fuel ratio must be tightly controlled with a
narrow window of stoichiometry. Deviations outside of this window will greatly decrease conversion
efficiency. See Fig. 60 . For example, a RICH mixture will decrease HC and CO conversion efficiency, while a
LEAN mixture will decrease NOx conversion efficiency.

Fig. 60: 3-Way Catalyst Conversion Efficiency Chart
Courtesy of FORD MOTOR CO.

EXHAUST SYSTEM

The purpose of the exhaust system is to convey engine emissions from exhaust manifold to atmosphere. Engine
exhaust emissions are directed from engine exhaust manifold to catalytic converter through front exhaust pipe.
A Heated Oxygen Sensor (HO2S) is mounted on the front exhaust pipe before catalyst. Catalytic converter

2003 Ford Pickup F150

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

reduces concentration of Carbon Monoxide (CO), unburned Hydrocarbons (HCs) and Oxides of Nitrogen
(NOx) in exhaust emissions to an acceptable level. Reduced exhaust emissions are directed from catalytic
converter to a muffler through rear exhaust pipe. Another HO2S is mounted on rear exhaust pipe. Exhaust
emissions are then directed to atmosphere through an exhaust tailpipe.

Hardware

The downstream HO2S may be located after light off catalyst or underbody catalyst. Underbody catalyst may
be in-line with light off catalyst, or underbody catalyst may be common to 2 light off catalysts, forming a "Y"
pipe configuration.

Exhaust Manifold & Runners

Exhaust manifold runners collect exhaust gases from engine cylinders. The number of exhaust manifolds and
exhaust manifold runners depends on engine configuration and number of cylinders.

Exhaust Pipes

Exhaust pipes are usually treated during manufacturing with an anti-corrosive coating agent to increase the life
of the product. The pipes serve as guides for flow of exhaust gases from engine exhaust manifold through
catalytic converter and muffler.

Upstream & Downstream Heated Oxygen Sensors

Heated Oxygen Sensors (HO2S) provide PCM with voltage and frequency information related to oxygen
content of exhaust gas. For additional HO2S information, see HEATED OXYGEN SENSOR under PCM
INPUTS under COMPUTERIZED ENGINE CONTROLS.

Muffler

Mufflers are usually treated during manufacturing with an anti-corrosive coating agent to increase the life of the
product. The muffler reduces noise levels produced by engine, and it also reduces noise produced by exhaust
gases as they travel from catalytic converter to atmosphere.

EVAPORATIVE EMISSION SYSTEMS

FUEL EVAPORATIVE SYSTEMS

The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the fuel tank. Fuel vapor trapped in
fuel tank is vented through the vapor valve assembly on top of fuel tank. Fuel vapors leave the valve assembly
through a single vapor line and continue on to the EVAP canister for storage until vapors are purged into the
engine for burning. EVAP canister is located in engine compartment, in rear of vehicle near luggage
compartment or underneath vehicle along the frame rail. There are 2 different types of EVAP systems that may
be used:

z

ENHANCED EVAPORATIVE EMISSION SYSTEM

z

ON-BOARD REFUELING VAPOR RECOVERY EVAP SYSTEM

2003 Ford Pickup F150

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

ENHANCED EVAPORATIVE EMISSION SYSTEM

The enhanced Evaporative Emission (EVAP) system consists of a fuel tank, fuel filler cap, fuel tank mounted or
in-line fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted
or in-line Fuel Tank Pressure (FTP) sensor, EVAP canister purge valve, intake manifold hose assembly,
Canister Vent (CV) solenoid, PCM and connecting wires and fuel vapor hoses. The following list of
components and their specific operation corresponds to numbers in illustration. See Fig. 61 .

1. Enhanced EVAP system uses inputs from Engine Coolant Temperature (ECT) sensor, Intake Air

Temperature (IAT) sensor, Mass Airflow (MAF) sensor, Vehicle Speed Sensor (VSS) and Fuel Tank
Pressure (FTP) sensor to provide information about engine operating conditions to PCM. The Fuel Level
Input (FLI) and FTP sensor signals are used by PCM to determine activation of EVAP Monitor based on
presence of fuel vapor or fuel sloshing.

2. PCM calculates a variable duty cycle based on desired amount of purge vapor flow to intake manifold for

a given engine condition. PCM can then output the duty cycle to solenoid on EVAP canister purge valve.
PCM uses Enhanced EVAP system inputs to evacuate system, using EVAP canister purge valve, CV
solenoid to seal Enhanced EVAP system from atmosphere, and uses FTP sensor to observe total vacuum
lost for a period of time.

3. Canister Vent (CV) solenoid seals EVAP canister from atmospheric pressure. See Fig. 62 . This allows

EVAP canister purge valve to obtain fuel tank target vacuum during EVAP Leak Check Monitor.

4. PCM outputs a variable duty cycle signal (between zero and 100 percent) to solenoid on EVAP canister

purge valve. For additional EVAP canister purge valve information, see EVAP CANISTER PURGE
VALVE .

5. Fuel Tank Pressure (FTP) sensor monitors the fuel tank pressure during engine operation and

continuously transmits an input signal to the PCM. During the EVAP monitor testing, the FTP sensor
monitors the fuel tank pressure or vacuum bleed-up. See Fig. 63 and Fig. 64 .

6. The fuel tank mounted fuel vapor vent valve assembly, fuel tank mounted fuel vapor control valve (or

remote fuel vapor control valve) are used in Enhanced EVAP system to control flow of fuel vapor
entering engine. All of these valves also prevent fuel tank overfilling during refueling operation and
prevent liquid fuel from entering EVAP canister and EVAP canister purge valve under any vehicle
altitude, handling or rollover condition. The liquid/vapor fuel discriminator is part of fuel vapor control
valve assembly on Focus and ZX2 models.

The Enhanced EVAP system, including all fuel vapor hoses, can be checked when a leak is detected by PCM.
This can be done by pressurizing system using Rotunda Evaporative Emission Tester Kit (134-00056) or
equivalent, and leak (frequency) detector included with kit.

2003 Ford Pickup F150

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