Removal & Installation
A set of standard spark plugs usually requires replacement after about 30,000 miles (32,000-48,000 km), depending on your style of driving. In normal operation plug gap increases about 0.001 in. (0.025mm) for every 2500 miles (4000 km). As the gap increases, the voltage requirement of the plug also increases. It requires a greater voltage to jump the wider gap and about two to three times as much voltage to fire the plug at high speeds than at idle. The improved air/fuel ratio control of modern fuel injection combined with the higher voltage output of modern ignition systems will often allow an engine to run significantly longer on a set of standard spark plugs, but keep in mind that efficiency will drop as the gap widens (along with fuel economy and power).
When you're removing spark plugs, work on one at a time. Don't start by removing the plug wires all at once, because, unless you number them, they may become mixed up. Take a minute before you begin and number the wires with tape.
- Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool.
- On some applications, it may be necessary to remove the air cleaner assembly.
- Carefully twist the spark plug wire boot 1 / 2 turn to loosen it, then pull upward and remove the boot from the plug. Be sure to pull on the boot and not on the wire, otherwise the connector located inside the boot may become separated.
- Using compressed air, blow any water or debris from the spark plug well to assure that no harmful contaminants are allowed to enter the combustion chamber when the spark plug is removed. If compressed air is not available, use a rag or a brush to clean the area.
- Using a spark plug socket that is equipped with a rubber insert to properly hold the plug, turn the spark plug counterclockwise to loosen and remove the spark plug from the bore.
- Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced.
- Using a wire feeler gauge, check and adjust the spark plug gap. When using a gauge, the proper size should pass between the electrodes with a slight drag. The next larger size should not be able to pass while the next smaller size should pass freely.
- Carefully thread the plug into the bore by hand. If resistance is felt before the plug is almost completely threaded, back the plug out and begin threading again. In small, hard to reach areas, an old spark plug wire and boot could be used as a threading tool. The boot will hold the plug while you twist the end of the wire and the wire is supple enough to twist before it would allow the plug to crossthread.
- Carefully tighten the spark plug. These engine applications use a tapered seat plug.
- Apply a small amount of silicone dielectric compound to the end of the spark plug. This assures no water will enter and no corrosion will develop. It will also aid in removal of the boot when the time comes.
Use special care when reinstalling spark plug boots, to assure that the metal terminal within the boot is fully seated on the spark plug terminal and that the boot has not moved on the wire. If boot to wire movement has occurred, the boot will give a false visual impression of being fully seated. A good check to assure that boots have been properly assembled is to push sideways on the installed boots. If they have been correctly installed, a stiff boot, with only slight looseness, will be noted. If the terminal has not been properly seated on the sparkplug, only the resistance of the rubber boot will be felt when pushing sideways.
When it becomes necessary to replace spark plug wires, because of age or breakage, it is recommended that you purchase a wire set for your specific engine model. These wire sets are precut to the proper length, and already have the boots installed.
- Twist the boot 1 / 2 - turn before trying to pull the boot off. Pull only on the boot, pulling on the wire could cause separation or breakage.
- On 3.8L and 5.0L applications, disconnect the spark plug wire from the distributor cap in the same manner as the wire was disconnected from the spark plug. On the 4.6L engine, squeeze the locking tabs and twist the boot, while pulling upward from the coil.
- Remove the necessary wire retainer clips and separators and remove the spark plug wire.
- Disconnect the battery negative cable.
- Remove the air cleaner assembly.
- Remove the spark plug wire retainers.
- Replace one wire at a time. Match the length of the old wires to new, to ease installation.
Ensure that, when replacing plug wires, the wires are routed correctly and through the proper retainers. Failure to route the wires properly can lead to radio ignition noise and crossfiring of the plugs, or shorting of the leads to ground.
- Coat the spark plug terminal end (or inside of the plug boot) with dielectric compound, install the boot onto the spark plug. Make sure it "clicks" on.
- Route the wire through the necessary retainer clips and separators.
- Route the wires along the engine, keeping the proper clearances.
- Install the wire to the proper distributor cap or ignition coil terminal, making sure the boot is firmly seated. On the 4.6L engine, make sure the coil boot locking tabs are engaged. Keep the proper firing order.
- Install spark plug wire retainers.
- Install air cleaner assembly.
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/or coil(s). Replace any damaged wiring. If no physical damage is obvious, the wires can be checked with an ohmmeter for excessive resistance and continuity.
At every tune-up/inspection, visually check the spark plug cables for burns cuts, or breaks in the insulation. Check the boots and the nipples on the distributor cap and/or coil. Replace any damaged wiring.
Every 50,000 miles (80,000 Km) or 60 months, the resistance of the wires should be checked with an ohmmeter. Wires with excessive resistance will cause misfiring, and may make the engine difficult to start in damp weather.
To check resistance, disconnect plug wires (do only one at a time) from the spark plug and distributor cap or coil pack.