AutoZone 1991 Buick Riviera 3.8L SFI OHV 6cyl | Repair Guides | Engine Electrical | Spark Plugs & Wires | Spark Plug Wires | AutoZone.com

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    1991 Buick Riviera 3.8L SFI OHV 6cyl

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    Ford Crown Victoria, Mercury Grand Marquis, Marauder, Lincoln Town Car 1999-2005

    Spark Plug Wires

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    Removal & Installation





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    Fig. Grasp the plug wire and carefully twist the wire to release the retainer from the spark plug. If the plug wire is stubborn, a pair of special removal pliers is recommended to remove the wires from the plugs



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    Fig. Carefully remove the plug wire from the cylinder head



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    Fig. A special spark plug socket with a rubber insert is needed to remove the spark plugs. Typically the spark plugs require a 5/8 socket



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    Fig. Using a suitable drive tool and the special socket, loosen the spark plug and . . .



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    Fig. . . . remove the spark plug from the engine



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    Fig. Clean out the spark plug bore and threads before installing the new spark plug



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    Fig. An inspection of the old spark plugs will give a general idea of the condition of the motor, compare the spark plugs to the chart in this section



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    Fig. A piece of fuel line or a small hose is useful in installing the spark plugs to avoid stripping the threads

    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.

    1. Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool.
    2.  
    3. On some applications, it may be necessary to remove the air cleaner assembly.
    4.  
    5. 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.
    6.  
    7. 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.
    8.  


    NOTE
    Remove the spark plugs when the engine is cold, if possible, to prevent damage to the threads. If removal of the plugs is difficult, apply a few drops of penetrating oil or silicone spray to the area around the base of the plug, and allow it a few minutes to work.

    1. 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.
    2.  

    To install:

    1. Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced.
    2.  
    3. 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.
    4.  
    5. 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.
    6.  


    WARNING
    Do not use the spark plug socket to thread the plugs. Always carefully thread the plug by hand or using an old plug wire, or vacuum line, to prevent the possibility of crossthreading and damaging the cylinder head bore.

    1. Carefully tighten the spark plug. These engine applications use a tapered seat plug.
    2.  
    3. 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.
    4.  

    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.



    Click image to see an enlarged view

    Fig. Grasp the plug wire and carefully twist the wire to release the retainer from the spark plug



    Click image to see an enlarged view

    Fig. If the plug wire is stubborn, a pair of special removal pliers is recommended to remove the wires from the plugs



    Click image to see an enlarged view

    Fig. Carefully remove the plug wire from the cylinder head



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    Fig. Remove the plug wires from the ignition coil by squeezing the retaining tabs and carefully lifting the wires up



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    Fig. Disconnect the plug wire retaining clips from the wires and . . .



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    Fig. . . . remove the plug wires from the engine

    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.


    WARNING
    Use care when removing spark plug wire boots from spark plugs. Grasp the wire by the rubber boot. Twist and pull the boot and wire from the spark plug. Never pull on the plug wire directly, or it may become separated from the connector inside the boot.

    1. 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.
    2.  
    3. 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.
    4.  
    5. Remove the necessary wire retainer clips and separators and remove the spark plug wire.
    6.  
    7. Disconnect the battery negative cable.
    8.  
    9. Remove the air cleaner assembly.
    10.  
    11. Remove the spark plug wire retainers.
    12.  
    13. Replace one wire at a time. Match the length of the old wires to new, to ease installation.
    14.  


    NOTE
    Make a note of the wire placement to the cap (or coil pack) and routing to the engine so as to maintain correct firing order and proper clearances to engine parts that could cause damage to the wiring.

    To install:

    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.

    1. 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.
    2.  


    WARNING
    On the 4.6L engine, it is critical to vehicle operation that the spark plug wires be properly installed at the spark plugs and ignition coils. If one spark plug wire is not properly installed, both spark plugs connected to that ignition coil may not fire under load.

    1. Route the wire through the necessary retainer clips and separators.
    2.  
    3. Route the wires along the engine, keeping the proper clearances.
    4.  
    5. 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.
    6.  


    NOTE
    On the 4.6L engine, the spark plug boot must be positioned 45 degrees from crankshaft centerline (outboard and forward) to make sure the boot seal is fully seated.

    1. Install spark plug wire retainers.
    2.  
    3. Install air cleaner assembly.
    4.  

    Testing





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    Fig. Checking plug wire resistance through the distributor cap with an ohmmeter



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    Fig. Checking individual plug wire resistance with a digital ohmmeter

    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.



    Connect one lead of an ohmmeter to the spark plug side of the wire (make sure to contact the metal clip inside the boot).
     
    Attach the other lead of the ohmmeter to the distributor (coil pack) side of the wire. Again, make sure you contact the metal clip.
     
    Spark plug wire resistance is a function of length, the longer the wire the greater the resistance. You should replace any wire with a resistance over 7k ohms per foot.
     
    Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary ignition component is faulty.
     


    NOTE
    Whenever the high-tension wires are removed from the plugs, coil, or distributor, silicone grease must be applied to the boot before reconnection. Coat the entire interior surface with Ford silicone grease D7AZ-19A331-A or its equivalent.

     
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