1991 1999 ford explorer chilton User Manual

Heated Oxygen Sensors (HO2S)
OPERATION
The oxygen sensor supplies the computer with a signal which indicates a rich or lean condition during engine
operation. The input information assists the computer in determining the proper air/fuel ratio. A low voltage
signal from the sensor indicates too much oxygen in the exhaust (lean condition) and, conversely, a high
voltage signal indicates too little oxygen in the exhaust (rich condition).
Typical Heated Oxygen Sensor (H2OS)-most vehicles are equipped with...

Typical Heated Oxygen (HO2S) sensor mounting locations-Ranger shown, other models are
similar
Click to enlarge
TESTING WARNING
Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Back probe the
connector to properly read the voltage of the HO2S.
Disconnect the HO2S.
1. 
Measure the resistance between PWR and GND terminals of the sensor. If the reading is
approximately 6 ohms at 68°F (1°C). the sensors heater element is in good condition.
2. 
With the HO2S connected...

REMOVAL & INSTALLATION
1996-99 Explorer/Mountaineers use four heated oxygen sensors (HO2S), and V6 equipped Rangers use
three HO2Ss, and 2.3L and 2.5L engines use two HO2Ss for the engine control system. The heated
sensors are located before and after the dual converters in the exhaust pipes. On 5.0L and 1991-95
engines V6 engines, there are two sensors, one is located in the left exhaust manifold and the other in
the dual converter Y-pipe. 1991-95 2.3L engines use only one sensor.
Disconnect the...

Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A.
4. 
To install: Install the sensor in the mounting boss, then tighten it to 27-33 ft. lbs. (37-45 Nm).
5. 
Reattach the sensor electrical wiring connector to the engine wiring harness.
6. 
Lower the vehicle.
7. 
Connect the negative battery cable.
8. 
Idle Air Control (IAC) Valve
OPERATION
The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on
the side of the throttle...

IAC valve wiring harness connections
Click to enlarge
REMOVAL & INSTALLATION Disconnect the negative battery cable.
1. 
To remove the IAC valve, first disconnect the negative battery cable, then the IAC wire harness plug
Next, remove the two IAC valve attaching bolts ... HOW TO USE THIS BOOK
TESTING 541 

... and pull the valve from the intake manifold
Disengage the wiring harness connector from the IAC valve.
2. 
Remove the two retaining screws, then remove the IAC valve and discard the old gasket.
3. 
To install:
When installing the valve, always discard the old gasket and install it using a new one
Clean the IAC valve mounting surface on the throttle body of old gasket material.
4. 
Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining
screws to 71-106 inch...

The ECT sensor is mounted on the lower intake manifold near the water outlet/thermostat housing, except on
2.3L and 2.5L engines. On the 2.3L and 2.5L engine the ECT is mounted on the water outlet/thermostat
housing.
TESTING Disengage the engine wiring harness connector from the ECT sensor.
1. 
Connect an ohmmeter between the ECT sensor terminals, and set the ohmmeter scale on 200,000
ohms.
2. 
With the engine cold and the ignition switch in the OFFposition, measure and note the ECT sensor
resistance....

ECT sensor wire harness connections
REMOVAL & INSTALLATION Partially drain the engine cooling system until the coolant level is below the ECT sensor mounting
hole.
1. 
Disconnect the negative battery cable.
2. 
Most ECT sensors (arrow) can be found on the intake manifold, near the water outlet housing
Detach the wiring harness connector from the ECT sensor.
3. 
Using an open-end wrench, remove the coolant temperature sensor from the intake manifold.
4. 
To install: Thread the sensor into the intake...

Refill the engine cooling system.
7. 
Start the engine, check for coolant leaks and top off the cooling system.
8. 
Intake Air Temperature (IAT) Sensor
OPERATION
The Intake Air Temperature (IAT) sensor resistance changes in response to the intake air temperature. The
sensor resistance decreases as the surrounding air temperature increases. This provides a signal to the PCM
indicating the temperature of the incoming air charge.
Most engines mount the IAT sensor in the air cleaner-to-throttle body supply...

To remove the IAT sensor, disconnect the wire harness plug ...
Disengage the wiring harness connector from the IAT sensor.
2. 
Remove the sensor from the air cleaner outlet tube.
3. 
... then loosen and remove the sensor from its mounting boss
To install:
Wipe down the air cleaner outlet tube and IAT sensor mounting boss to clean the sensor area of all
dirt and grime.
4. 
Install the sensor into the air cleaner outlet tube securely.
5. 
Attach the wiring harness connector to the IAT sensor.
6. 
Connect...