1991 1999 ford explorer chilton User Manual

							Testing the spark plug wire resistance through the distributor cap with an ohmmeter
Remove the distributor cap from the distributor assembly.
1. 
Visually inspect the spark plug wires for burns, cuts or breaks in the insulation. Check the spark plug
boots and the nipples on the distributor cap and coil. Replace any damaged wiring.
2. 
Inspect the spark plug wires to insure that they are firmly seated on the distributor cap.
3. 
Disconnect the spark plug wire thought to be defective at the spark plug.
4. 
Using an ohmmeter, measure the resistance between the distributor cap terminal and the spark plug
terminal.
5. 
Make certain that a good connection exists between the distributor cap and the spark terminal. Never,
under any circumstances, measure resistance by puncturing the spark plug wire.
If the measured resistance is less than 7000 ohms per foot of wire, the wire is good. If the measured
resistance is greater than 7000 ohms per foot, the wire is defective and should be replaced.
6. 
Without Distributor Visually inspect the spark plug wires for burns, cuts or breaks in the insulation. Check the spark plug
boots and the nipples on the coil. Replace any damaged wiring.
1. 
Inspect the spark plug wires to insure that they are firmly seated on the coil pack.
2. 
Disconnect the spark plug wire thought to be defective at the spark plug.
3. 
Using an ohmmeter, measure the resistance between the coil terminal and the spark plug terminal.
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TESTING 87 
						

							Checking individual plug wire resistance with a digital ohmmeter
Never, under any circumstances, measure resistance by puncturing the spark plug wire.
If the measured resistance is less than 7000 ohms per foot of wire, the wire is good. If the measured
resistance is greater than 7000 ohms per foot, the wire is defective and should be replaced.
5. 
Distributor Cap and Rotor
1991-92 models with the 2.9L engine, and 1991-94 models with the 3.0L engine use a distributor
equipped ignition system. All other models use a distributorless ignition.
REMOVAL & INSTALLATION
Distributor Cap As a precaution, label all of the spark plug wires with their perspective cylinder number.
1. 
Loosen the cap hold-down screws.
2. 
Remove the cap by lifting straight up to prevent damage to the rotor blade and spring.
3. 
If the plug wires do not have enough slack to allow cap removal, confirm that they are properly labeled
and remove them from the cap.
Installation is the reverse of the removal procedure. Note the position of the square alignment locator
and tighten the hold-down screws to 18-23 inch pounds (2.0-2.6Nm)
4. 
Distributor Rotor Remove the distributor cap.
1. 
Pull straight up on the rotor to disengage it from the shaft and armature.
2. 
Installation is the reverse of the removal procedure. Align the locating boss on the rotor with the hole
on the armature, then insure that it is fully seated on the shaft.
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88 Distributor Cap and Rotor 
						

							
INSPECTION
Distributor Cap
Inspection points for the distributor cap-note the square alignment locator which limits the cap to one installation position
Wash the inside and outside surfaces of the cap with soap and water then dry it with compressed air.
1. 
Inspect the cap for cracks, broken or worn carbon button, or carbon tracks. Also inspect the cap
terminals for dirt and corrosion.
2. 
Replace the cap if any of the above conditions are observed.
3. 
Distributor Rotor
Inspection points for the distributor rotor-note the locating boss which fits in the armature Click to enlarge
Wash the rotor with soap and water then dry with it compressed air.
1. 
Inspect the rotor for cracks, carbon tracks, burns or damage to the blade or spring.
2. 
Replace the rotor if any of the above conditions are observed.
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INSPECTION 89 
						

							
Ignition Timing
No periodic checking or adjustment of the ignition timing is necessary for any of the vehicles covered by
this manual. However, the distributor ignition system used by the 1991-94 2.9L and 3.0L engines does
allow for both, should the distributor be removed and installed or otherwise disturbed.
GENERAL INFORMATION
Ignition timing is the measurement, in degrees of crankshaft rotation, of the point at which the spark plugs fire
in each of the cylinders. It is measured in degrees before or after Top Dead Center (TDC) of the compression
stroke.
Because it takes a fraction of a second for the spark plug to ignite the mixture in the cylinder, the spark plug
must fire a little before the piston reaches TDC. Otherwise, the mixture will not be completely ignited as the
piston passes TDC and the full power of the explosion will not be used by the engine.
The timing measurement is given in degrees of crankshaft rotation before the piston reaches TDC (BTDC). If
the setting for the ignition timing is 5° BTDC, the spark plug must fire 5° before each piston reaches TDC.
This only holds true, however, when the engine is at idle speed.
As the engine speed increases, the pistons go faster. The spark plugs have to ignite the fuel even sooner if it is
to be completely ignited when the piston reaches TDC. On all engines covered by this manual, spark timing
changes are accomplished electronically by the engine and ignition control computers.
If the ignition is set too far advanced (BTDC), the ignition and expansion of the fuel in the cylinder will occur
too soon and tend to force the piston down while it is still traveling up. This causes engine ping. If the ignition
spark is set too far retarded, after TDC (ATDC), the piston will have already passed TDC and started on its
way down when the fuel is ignited. This will cause the piston to be forced down for only a portion of its
travel. This will result in poor engine performance and lack of power.
Timing marks consisting of O marks or scales can be found on the rim of the crankshaft pulley and the timing
cover. The mark(s) on the pulley correspond(s) to the position of the piston in the number 1 cylinder. A
stroboscopic (dynamic) timing light is used, which is hooked into the circuit of the No. 1 cylinder spark plug.
Every time the spark plug fires, the timing light flashes. By aiming the timing light at the timing marks while
the engine is running, the exact position of the piston within the cylinder can be easily read since the
stroboscopic flash makes the pulley appear to be standing still. Proper timing is indicated when the mark and
scale are in proper alignment.
Because these vehicles utilize high voltage, electronic ignition systems, only a timing light with an inductive
pickup should be used. This pickup simply clamps onto the No. 1 spark plug wire, eliminating the adapter. It
is not susceptible to cross-firing or false triggering, which may occur with a conventional light, due to the
greater voltages produced by electronic ignition.
INSPECTION & ADJUSTMENT
1991-94 2.9L and 3.0L Engines
SETTING INITIAL (BASE) TIMING
Specific instructions and specifications for setting initial timing can be found in the Vehicle Emission
Control Information (VECI) label in the engine compartment. Because this label contains information
regarding any specific calibration requirements for YOUR vehicle, those instructions and specifications HOW TO USE THIS BOOK
90 Ignition Timing 
						

							
should be followed if they differ from the following.
The underhood VECI label is specific to YOUR truck and should be used if it differs from another source
This procedure should not be used as a periodic maintenance adjustment. Timing should only be set after the
distributor has been disturbed (removed and re-installed) in some way. If problems are encountered setting
the initial timing with this procedure and no mechanical causes are found, follow the spark timing advance
check procedure found later in this section.
Do not change the ignition timing by the use of a different octane rod without having the proper
authority to do so. Federal emission requirements will be affected.
Start the engine and allow it to run until it reaches normal operating temperature.
1. 
CAUTION
NEVER run an engine in a garage or building without proper ventilation. Carbon monoxide will quickly enter
the body, excluding oxygen from the blood stream. This condition will cause dizziness, sleepiness and
eventually death.
Once normal operating temperature has been reached, shut the engine OFF.
2. 
Firmly apply the parking brake and block the drive wheels. Place the transmission in P(A/T) or
NEUTRAL(M/T, as applicable).
3. 
Make sure heater and A/C, along with all other accessories are in the OFF position.
4. 
Connect an inductive timing light, such as the Rotunda 059-00006 or equivalent, to the No. 1 spark
plug wire, according the tool manufacturers instructions.
5. 
Connect a tachometer to the ignition coil connection using an alligator clip. This can be done by
inserting the alligator clip into the back of the connector, onto the dark green/yellow dotted wire.
6. 
DO NOT allow the alligator clip to accidentally ground to a metal surface while attached to the coil
connector as that could permanently damage the ignition coil.
Disconnect the single wire in-line SPOUT connector which connects the control computer (usually
terminal 36) to the ignition control module. This will prevent the electronic ignition from advancing
the timing during the set procedure.
7. 
Using a suitable socket or wrench, loosen the distributor hold-down bolt slightly at this time, BUT
DO NOT ALLOW THE DISTRIBUTOR TO MOVE or timing will have to be set regardless of the
current conditions.
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INSPECTION & ADJUSTMENT 91 
						

							
A remote starter must NOT be used to start the vehicle when setting the initial ignition timing.
Disconnecting the start wire at the starter relay will cause the ignition control module to revert to Start
Mode timing after the vehicle is started. Reconnecting the start wire after the vehicle is running WILL
NOT correct the timing.
Start the engine (using the ignition key and NOT a remote starter to assure timing will be set
correctly) and allow the engine to return to normal operating temperature.
9. 
With the engine running at the specified rpm, check the initial timing. If adjustments must be made,
rotate the distributor while watching the timing marks. Once proper adjustment has been reached,
make sure the distributor is not disturbed until the hold-down bolt can be secured.
10. 
Reconnect the single wire in-line SPOUT connector and check the timing to verify that the distributor
is now advancing beyond the initial setting.
11. 
Shut the engine OFFand tighten the distributor bolt while CAREFULLY holding the distributor from
turning. If the distributor moves, you will have to start the engine and reset the timing.
12. 
Restart the engine and repeat the procedure to check the timing and verify that it did not change
13. 
Shut the engine OFF, then disconnect the tachometer and timing light.
14. 
CHECKING SPARK TIMING ADVANCE
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 in-line connector and the TFI
connector.
8. 
Except 1991-94 2.9L and 3.0L Engines
These engines utilize a Distributorless Ignition System (DIS). On this system, ignition coil packs fire the
spark plugs directly through the spark plug wires. All spark timing and advance is determined by the ignition
control module and engine control computer. No ignition timing adjustments are necessary or possible.
Valve Lash
No periodic valve lash adjustments are necessary on these engines. All the engines utilize hydraulic
valvetrains to automatically maintain proper valve lash.
Idle Speed and Mixture Adjustments
The engines covered by this manual utilize sophisticated multi-port fuel injection systems in which an engine
control computer utilizes information from various sensors to control idle speed and air fuel mixtures. No
periodic adjustments are either necessary or possible on these systems. If a problem is suspected, please refer
to Sections 4 and 5 of this manual for more information on electronic engine controls and fuel injection. HOW TO USE THIS BOOK
92 INSPECTION & ADJUSTMENT 
						

							
Air Conditioning System
SYSTEM SERVICE & REPAIR
It is recommended that the A/C system be serviced by an EPA Section 609 certified automotive
technician utilizing a refrigerant recovery/recycling machine.
The do-it-yourselfer should not service his/her own vehicles A/C system for many reasons, including legal
concerns, personal injury, environmental damage and cost.
According to the U.S. Clean Air Act, it is a federal crime to service or repair (involving the refrigerant) a
Motor Vehicle Air Conditioning (MVAC) system for money without being EPA certified. It is also illegal to
vent R-12 and R-134a refrigerants into the atmosphere. State and/or local laws may be more strict than the
federal regulations, so be sure to check with your state and/or local authorities for further information.
Federal law dictates that a fine of up to $25,000 may be levied on people convicted of venting
refrigerant into the atmosphere.
When servicing an A/C system you run the risk of handling or coming in contact with refrigerant, which may
result in skin or eye irritation or frostbite. Although low in toxicity (due to chemical stability), inhalation of
concentrated refrigerant fumes is dangerous and can result in death; cases of fatal cardiac arrhythmia have
been reported in people accidentally subjected to high levels of refrigerant. Some early symptoms include loss
of concentration and drowsiness.
Generally, the limit for exposure is lower for R-134a than it is for R-12. Exceptional care must be
practiced when handling R-134a.
Also, some refrigerants can decompose at high temperatures (near gas heaters or open flame), which may
result in hydrofluoric acid, hydrochloric acid and phosgene (a fatal nerve gas).
It is usually more economically feasible to have a certified MVAC automotive technician perform A/C system
service on your vehicle.
R-12 Refrigerant Conversion
If your vehicle still uses R-12 refrigerant, one way to save A/C system costs down the road is to investigate
the possibility of having your system converted to R-134a. The older R-12 systems can be easily converted
to R-134a refrigerant by a certified automotive technician by installing a few new components and changing
the system oil.
The cost of R-12 is steadily rising and will continue to increase, because it is no longer imported or
manufactured in the United States. Therefore, it is often possible to have an R-12 system converted to
R-134a and recharged for less than it would cost to just charge the system with R-12.
If you are interested in having your system converted, contact local automotive service stations for more
details and information.
PREVENTIVE MAINTENANCE
Although the A/C system should not be serviced by the do-it-yourselfer, preventive maintenance should be
practiced to help maintain the efficiency of the vehicles A/C system. Be sure to perform the following: HOW TO USE THIS BOOK
Air Conditioning System 93 
						

							The easiest and most important preventive maintenance for your A/C system is to be sure that it is
used on a regular basis. Running the system for five minutes each month (no matter what the season)
will help ensure that the seals and all internal components remain lubricated.
· 
Some vehicles automatically operate the A/C system compressor whenever the windshield defroster is
activated. Therefore, the A/C system would not need to be operated each month if the defroster was
used.
In order to prevent heater core freeze-up during A/C operation, it is necessary to maintain proper
antifreeze protection. Be sure to properly maintain the engine cooling system.
· 
Any obstruction of or damage to the condenser configuration will restrict air flow which is essential to
its efficient operation. Keep this unit clean and in proper physical shape.
· 
Bug screens which are mounted in front of the condenser (unless they are original equipment) are
regarded as obstructions.
The condensation drain tube expels any water which accumulates on the bottom of the evaporator
housing into the engine compartment. If this tube is obstructed, the air conditioning performance can
be restricted and condensation buildup can spill over onto the vehicles floor.
· 
SYSTEM INSPECTION
Although the A/C system should not be serviced by the do-it-yourselfer, system inspections should be
performed to help maintain the efficiency of the vehicles A/C system. Be sure to perform the following:
The easiest and often most important check for the air conditioning system consists of a visual inspection of
the system components. Visually inspect the system for refrigerant leaks, damaged compressor clutch,
abnormal compressor drive belt tension and/or condition, plugged evaporator drain tube, blocked condenser
fins, disconnected or broken wires, blown fuses, corroded connections and poor insulation.
A refrigerant leak will usually appear as an oily residue at the leakage point in the system. The oily residue
soon picks up dust or dirt particles from the surrounding air and appears greasy. Through time, this will build
up and appear to be a heavy dirt impregnated grease.
For a thorough visual and operational inspection, check the following: Check the surface of the radiator and condenser for dirt, leaves or other material which might block
air flow.
· 
Check for kinks in hoses and lines. Check the system for leaks.
· 
Make sure the drive belt is properly tensioned. During operation, make sure the belt is free of noise or
slippage.
· 
Make sure the blower motor operates at all appropriate positions, then check for distribution of the air
from all outlets.
· 
Remember that in high humidity, air discharged from the vents may not feel as cold as expected, even if
the system is working properly. This is because moisture in humid air retains heat more effectively than
dry air, thereby making humid air more difficult to cool.
Windshield Wipers HOW TO USE THIS BOOK
94 PREVENTIVE MAINTENANCE 
						

							
ELEMENT (REFILL) CARE & REPLACEMENT
For maximum effectiveness and longest element life, the windshield and wiper blades should be kept clean.
Dirt, tree sap, road tar and so on will cause streaking, smearing and blade deterioration if left on the glass. It is
advisable to wash the windshield carefully with a commercial glass cleaner at least once a month. Wipe off
the rubber blades with the wet rag afterwards. Do not attempt to move wipers across the windshield by hand;
damage to the motor and drive mechanism will result.
To inspect and/or replace the wiper blade elements, place the wiper switch in the LOWspeed position and the
ignition switch in the ACCposition. When the wiper blades are approximately vertical on the windshield, turn
the ignition switch to OFF.
Examine the wiper blade elements. If they are found to be cracked, broken or torn, they should be replaced
immediately. Replacement intervals will vary with usage, although ozone deterioration usually limits element
life to about one year. If the wiper pattern is smeared or streaked, or if the blade chatters across the glass, the
elements should be replaced. It is easiest and most sensible to replace the elements in pairs.
If your vehicle is equipped with aftermarket blades, there are several different types of refills and your vehicle
might have any kind. Aftermarket blades and arms rarely use the exact same type blade or refill as the original
equipment.
Regardless of the type of refill used, be sure to follow the part manufacturers instructions closely. Make sure
that all of the frame jaws are engaged as the refill is pushed into place and locked. If the metal blade holder
and frame are allowed to touch the glass during wiper operation, the glass will be scratched.
Most aftermarket blades are available with multiple adapters to fit different vehicles HOW TO USE THIS BOOK
ELEMENT (REFILL) CARE & REPLACEMENT 95 
						

							Choose a blade which will fit your vehicle, and that will be readily available next time you need
blades
When installed, be certain the blade is fully inserted into the backing
Tires and Wheels
Common sense and good driving habits will afford maximum tire life. Make sure that you dont overload the
vehicle or run with incorrect pressure in the tires. Either of these will increase tread wear. Fast starts, sudden
stops and sharp cornering are hard on tires and will shorten their useful life span.
For optimum tire life, keep the tires properly inflated, rotate them often and have the wheel alignment
checked periodically.
Inspect your tires frequently. Be especially careful to watch for bubbles in the tread or sidewall, deep cuts or
underinflation. Replace any tires with bubbles in the sidewall. If cuts are so deep that they penetrate to the
cords, discard the tire. Any cut in the sidewall of a radial tire renders it unsafe. Also look for uneven tread
wear patterns that may indicate the front end is out of alignment or that the tires are out of balance. HOW TO USE THIS BOOK
96 Tires and Wheels