1991 1999 ford explorer chilton User Manual

							View of the TFI-IV ignition system components
Click to enlarge
SYSTEM OPERATION
The CMP sensor, housed inside the distributor, responds to a rotating metallic shutter mounted on the
distributor shaft. This rotating shutter produces a digital Profile Ignition Pick-up (PIP) signal, which is used
by the PCM and ICM to provide base timing information, determine engine speed (rpm) and crankshaft
position. The distributor shaft rotates at one-half crankshaft speed, therefore the shutter rotates once for every
two crankshaft revolutions.
The ICM functions in either one of two modes: push start or Computer Controlled Dwell (CCD). The push
start mode allows for increased dwell, or coil on time, when starting the engine. During this mode, the ICM
determines when to turn on the ignition coil based on engine speed information. The coil is turned off, thereby
firing, whenever a rising edge of a SPark OUTput (SPOUT) signal is received. The SPOUT signal is
generated by the PCM, and provides spark timing information to the ICM. During the push start mode, the
SPOUT signal only indicates the timing for coil firing; the falling edge of the SPOUT signal is ignored.
Despite the name, the push start mode is also enabled during engine starting with the ignition key.
Do not attempt to push start a vehicle equipped with an automatic transmission.
The rotary armature has open areas called windows and tabs called vanes
The vane interrupts the magnetic field passing through the Hall effect device HOW TO USE THIS BOOK
170 General Information 
						

							
During the CCD mode, both edges of the SPOUT signal are utilized. The leading edge of the SPOUT signal is
used by the ICM in the same manner as during the push start mode. The falling edge of the signal is generated
to control the timing for turning the ignition coil on (the ICM no longer controls this function as during the
push start mode). During the CCD mode, the coil on time, or dwell, is entirely controlled by the PCM through
the SPOUT signal.
In the event that the SPOUT signal from the PCM is disrupted, the ICM will use the PIP signal from the CMP
to fire the ignition coil, which results in a fixed spark angle and dwell.
Diagnosis and Testing
SERVICE PRECAUTIONS Always turn the keyOFFand isolate both ends of a circuit whenever testing for shorts or continuity.
· 
Never measure voltage or resistance directly at the processor connector.
· 
Always disconnect solenoids and switches from the harness before measuring for continuity,
resistance or energizing by way of a 12-volt source.
· 
When disconnecting connectors, inspect for damaged or pushed-out pins, corrosion, loose wires, etc.
Service if required.
· 
PRELIMINARY CHECKS Visually inspect the engine compartment to ensure that all vacuum lines and spark plug wires are
properly routed and securely connected.
1. 
Examine all wiring harness and connectors for insulation damage, burned, overheated, loose or
broken conditions. Ensure that the ICM is securely fastened to the front fender apron.
2. 
Be certain that the battery is fully charged and that all accessories are OFF during the diagnosis.
3. 
TEST PROCEDURES
Perform the test procedures in the order in which they are presented here.
Ignition Coil Secondary Voltage Test
CRANK MODE
Connect a spark tester between the ignition coil wire and a good engine ground.
1. 
Crank the engine and check for spark at the tester.
2. 
Turn the ignition switch OFF.
3. 
If no spark occurs, check the following: Inspect the ignition coil for damage or carbon tracking.
1. 
Check that the distributor shaft is rotating when the engine is being cranked.
2. 
If the results in Steps a and b are okay, go to Module Test.
3. 
4. 
If a spark did occur, check the distributor cap and rotor for damage or carbon tracking. Go to the
Ignition Coil Secondary Voltage (Run Mode) Test.
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SYSTEM OPERATION 171 
						

							Secondary coil voltage test 1 chart-crank mode check
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RUN MODE
Fully apply the parking brake. Place the gear shift lever in Neutral (manual transmission) or Park
(automatic transmission).
1. 
Disconnect the Sterminal wire at the starter relay. Attach a remote starter switch.
2. 
Turn the ignition switch to theRUNposition.
3. 
Using the remote starter switch, crank the engine and check for spark.
4. 
Turn the ignition switchOFF.
5. 
If no spark occurred, the problem lies with the wiring harness. Inspect the wiring harness for short
circuits, open circuits and other defects.
6. 
If a spark did occur, the problem is not in the ignition system.
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172 TEST PROCEDURES 
						

							Secondary coil voltage test 2 chart-run mode check
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TEST PROCEDURES 173 
						

							Wiring harness test 3 chart-voltage check
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174 TEST PROCEDURES 
						

							Distributor hall effect test 4 chart
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ICM Test Remove the ICM from the distributor or the front fender apron.
1. 
Measure the resistance between the ICM terminals as shown below: GND-PIP IN: should be greater than 500 ohms.
1. 
PIP PWR-PIP IN: should be less than 2,000 ohms.
2. 
PIP PWR-TFI PWR: should be less than 200 ohms.
3. 
GND-IGN GND: should be less than 2 ohms.
4. 
PIP IN-PIP: should be less than 200 ohms.
5. 
2. 
If any of these checks failed, replace the ICM with a new one.
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TEST PROCEDURES 175 
						

							ICM module resistance test 5 chart
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ICM module test 6 chart Click to enlarge
System Test Disconnect the pin-in-line connector near the ICM.
1. 
Crank the engine
2. 
Turn the ignition switch OFF.
3. 
If a spark did occur, check the PIP and ignition ground wires for continuity. If okay, the problem is
not in the ignition system.
4. 
If no spark occurs, check the voltage at the positive (+) terminal of the ignition coil with the ignition
switch in RUN.
5. 
If the reading is not within battery voltage, check for a worn or damaged ignition switch.
6. 
If the reading is within battery voltage, check for faults in the wiring between the coil and TFI module
terminal No. 2 or any additional wiring or components connected to that circuit.
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176 TEST PROCEDURES 
						

							Schematic of the TFI-IV ignition system
Click to enlarge
Spark Timing Advance Test
Spark timing advance is controlled by the EEC system. This procedure checks the capability of the ignition
module to receive the spark timing command from the EEC module. The use of a volt/ohmmeter is required.
Turn the ignition switch OFF.
1. 
Disconnect the pin-in-line connector (SPOUT connector) near the TFI module.
2. 
Start the engine and measure the voltage, at idle, from the SPOUT connector to the distributor base.
The reading should equal battery voltage.
3. 
If the result is okay, the problem lies within the EEC-IV system.
4. 
If the result was not satisfactory, separate the wiring harness connector from the ignition module.
Check for damage, corrosion or dirt. Service as necessary.
5. 
Measure the resistance between terminal No. 5 and the pin-in-line connector. This test is done at the
ignition module connector only. The reading should be less than 5 ohms.
6. 
If the reading is okay, replace the TFI module.
7. 
If the result was not satisfactory, service the wiring between the pin inline connector and the TFI
connector.
8. 
Ignition Coil
TESTING
Ignition Coil and Secondary Wire Disconnect the ignition coil connector and check for dirt, corrosion or damage.
1. 
Substitute a known-good coil and check for spark using the spark tester.
2. 
Dangerous high voltage may be present when performing this test. Do not hold the coil while
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TEST PROCEDURES 177 
						

							Secondary coil wire test 7 chart
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Crank the engine and check for spark.
3. 
Turn the ignition switch OFF.
4. 
If a spark did occur, measure the resistance of the ignition coil wire, replace it if the resistance is
greater than 7000 ohms per foot. If the readings are within specification, replace the ignition coil.
5. 
If no spark occurs, the problem is not the coil.
6. 
Ignition Coil Supply Voltage Remove the/coil connector.
1. 
Attach the negative (-) lead from a Volt/ohmmeter to the distributor base.
2. 
Measure the battery voltage.
3. 
Turn the ignition switch to the RUNposition.
4. 
Measure the voltage at the positive (+) terminal of the ignition coil. If the reading is at least 90% of
battery voltage, check the ignition coil connector for dirt, corrosion and damage. Check the ignition
coil terminals for dirt, corrosion and damage; if no problem is found, replace the ignition coil. If the
reading is less than 90% of battery voltage, check the wiring between the ignition coil and ignition
switch, or for a worn or damaged ignition switch.
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178 TESTING 
						

							Ignition coil supply voltage test 8 chart
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Ignition Coil Primary Resistance Test Turn the ignition switch off, then disconnect the ignition coil connector.
1. 
Check for dirt, corrosion or damage.
2. 
Ignition coil primary resistance test
Use an ohmmeter to measure the resistance from the positive (+) to negative (-) terminals of the
ignition coil.
3. 
If the reading is between 0.3-1.0 ohms the ignition coil is OK; continue on to the Ignition Coil
Secondary Resistance Test. If the reading is less than 0.3 ohms or greater than 1.0 ohms , replace the
ignition coil.
4. 
Ignition Coil Secondary Resistance Test Use an ohmmeter to measure the resistance between the negative (-) terminal to the high voltage
terminal of the ignition coil.
1. 
If the reading is between 6,500-11,500 ohms, the ignition coil is OK. If the reading is less than 6500
ohms or more than 11,500 ohms , replace the ignition coil.
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TESTING 179