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 multiple sensors
The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated
oxygen sensors are used on all models to allow the engine to reach the closed loop faster. HOW TO USE THIS BOOK
Heated Oxygen Sensors (HO2S) 537 
						

							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 and engine running, measure the voltage with a Digital Volt-Ohmmeter
(DVOM) between terminals HO2Sand SIG RTN(GND) of the oxygen sensor connector. If the
voltage readings are swinging rapidly between 0.01-1.1 volts, the sensor is probably okay.
3.  HOW TO USE THIS BOOK
538 OPERATION 
						

							
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 negative battery cable.
1. 
Raise and safely support the vehicle on jackstands.
2. 
From underneath, locate the oxygen sensor (arrow), which is screwed into an exhaust component
Disconnect the HO2S from the engine control sensor wiring.
3. 
If excessive force is needed to remove the sensors, lubricate the sensor with penetrating oil prior to
removal.
Using the proper wrench, loosen the oxygen sensor. Ensure that the wire and connector are unplugged
HOW TO USE THIS BOOK
REMOVAL & INSTALLATION 539 
						

							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 body. This valve allows air, determined by the Powertrain Control Module (PCM) and
controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.
Typical Idle Air Control (IAC) valve which is mounted to the throttle body-cutaway view shows air bypass direction Click to enlarge
TESTING Turn the ignition switch to the OFFposition.
1. 
Disengage the wiring harness connector from the IAC valve .
2. 
Using an ohmmeter, measure the resistance between the terminals of the valve.
3. 
Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWRterminal and the
negative lead on the ISCterminal.
If the resistance is not 7-13 ohms, replace the IAC valve.
4.  HOW TO USE THIS BOOK
540 Idle Air Control (IAC) Valve 
						

							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 lbs. (8-12 Nm).
5. 
Attach the wiring harness connector to the IAC valve.
6. 
Connect the negative battery cable.
7. 
Engine Coolant Temperature (ECT) Sensor
OPERATION
The engine coolant temperature sensor resistance changes in response to engine coolant temperature. The
sensor resistance decreases as the surrounding temperature increases. This provides a reference signal to the
PCM, which indicates engine coolant temperature. HOW TO USE THIS BOOK
542 REMOVAL & INSTALLATION 
						

							
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. Attach the engine wiring harness connector to the sensor.
3. 
Start the engine and allow the engine to warm up to normal operating temperature.
4. 
Once the engine has reached normal operating temperature, turn the engine OFF
5. 
Once again, detach the engine wiring harness connector from the ECT sensor.
6. 
Measure and note the ECT sensor resistance, then compare the cold and hot ECT sensor resistance
measurements with the accompanying chart.
7. 
Replace the ECT sensor if the readings do not approximate those in the chart, otherwise reattach the
engine wiring harness connector to the sensor.
8. 
Submerge the end of the temperature sensor in cold or hot water and check resistance HOW TO USE THIS BOOK
OPERATION 543 
						

							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 manifold by hand, then tighten it securely.
5. 
Connect the negative battery cable.
6.  HOW TO USE THIS BOOK
544 TESTING 
						

							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 tube. However, some earlier
engines have it mounted to the upper intake manifold.
TESTING
Turn the ignition switch OFF. Disengage the wiring harness connector from the IAT sensor.
1. 
Using a Digital Volt-Ohmmeter (DVOM), measure the resistance between the two sensor terminals.
2. 
Compare the resistance reading with the accompanying chart. If the reading for a given temperature is
approximately that shown in the table, the IAT sensor is okay.
3. 
Attach the wiring harness connector to the sensor.
4. 
IAT sensor wiring harness connections
REMOVAL & INSTALLATION Disconnect the negative battery cable.
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REMOVAL & INSTALLATION 545 
						

							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 the negative battery cable.
7. 
Mass Air Flow (MAF) Sensor
OPERATION
The Mass Air Flow (MAF) sensor directly measures the amount of the air flowing into the engine. The sensor
is mounted between the air cleaner assembly and the air cleaner outlet tube. HOW TO USE THIS BOOK
546 REMOVAL & INSTALLATION