1991 1999 ford explorer chilton User Manual
Have a look at the manual 1991 1999 ford explorer chilton User Manual online for free. It’s possible to download the document as PDF or print. UserManuals.tech offer 41 Ford manuals and user’s guides for free. Share the user manual or guide on Facebook, Twitter or Google+.
CV-boots must be inspected periodically for damage A torn boot should be replaced immediately Spark Plugs A typical spark plug consists of a metal shell surrounding a ceramic insulator. A metal electrode extends downward through the center of the insulator and protrudes a small distance. Located at the end of the plug and attached to the side of the outer metal shell is the side electrode. The side electrode bends in at a 90( angle so that its tip is just past and parallel to the tip of the center electrode. The distance between these two electrodes (measured in thousandths of an inch or hundredths of a millimeter) is called the spark plug gap. The spark plug does not produce a spark, but instead provides a gap across which the current can arc. The coil produces anywhere from 20,000 to 50,000 volts (depending on the type and application) which travels through the wires to the spark plugs. The current passes along the center electrode and jumps the gap to the side electrode, and in doing so, ignites the air/fuel mixture in the combustion chamber. HOW TO USE THIS BOOK INSPECTION 77
Cross-section of a spark plug Click to enlarge A variety of tools and gauges are needed for spark plug service SPARK PLUG HEAT RANGE Spark plug heat range is the ability of the plug to dissipate heat. The longer the insulator (or the farther it extends into the engine), the hotter the plug will operate; the shorter the insulator (the closer the electrode is to the blocks cooling passages) the cooler it will operate. A plug that absorbs little heat and remains too cool will quickly accumulate deposits of oil and carbon since it is not hot enough to burn them off. This leads to plug fouling and consequently to misfiring. A plug that absorbs too much heat will have no deposits but, due to the excessive heat, the electrodes will burn away quickly and might possibly lead to preignition or other HOW TO USE THIS BOOK 78 Spark Plugs
ignition problems. Preignition takes place when plug tips get so hot that they glow sufficiently to ignite the air/fuel mixture before the actual spark occurs. This early ignition will usually cause a pinging during low speeds and heavy loads. Spark plug heat rangeClick to enlarge The general rule of thumb for choosing the correct heat range when picking a spark plug is: if most of your driving is long distance, high speed travel, use a colder plug; if most of your driving is stop and go, use a hotter plug. Original equipment plugs are generally a good compromise between the 2 styles and most people never have the need to change their plugs from the factory-recommended heat range. HOW TO USE THIS BOOK SPARK PLUG HEAT RANGE 79
REMOVAL & INSTALLATION Always twist and pull on the spark plug boot, never on the wire Ford recommends replacing standard spark plugs every 30,000 miles (48,000km) and platinum plugs every 60,000 miles (96,000km). A set of spark plugs usually requires replacement after about 20,000-30,000 miles (32,000-48,000km), depending on your style of driving. In normal operation plug gap increases about 0.001 in. (0.025mm) for every 2500 miles (4000km). As the gap increases, the plugs voltage requirement 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 youre removing spark plugs, work on one at a time. Dont 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. Also, an anti-seize compound should be used before installing the plugs into the cylinder head. Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool. 1. Carefully twist the spark plug wire boot 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. 2. HOW TO USE THIS BOOK 80 REMOVAL & INSTALLATION
Remove the spark plug wire from the plug by twisting the boot and pulling outwards. Never pull on the wire 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. 3. 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. 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. 4. Using the proper size spark plug socket, loosen the plug by rotating it counterclockwise Once the plug is loose, you should be able to remove it by hand. Compare the plug against the examples given WARNING Be sure not to use a flexible extension on the socket. Use of a flexible extension may allow a shear force to be applied to the plug. A shear force could break the plug off in the cylinder head, leading to costly and frustrating repairs. To install: HOW TO USE THIS BOOK REMOVAL & INSTALLATION 81
Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced. 5. 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. 6. Coat the spark plug threads with an anti-seize compound before installing it into the cylinder head. 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. 7. 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 to prevent the possibility of crossthreading and damaging the cylinder head bore. Carefully tighten the spark plug. If the plug you are installing is equipped with a crush washer, seat the plug, then tighten about 1 /4 turn to crush the washer. If you are installing a tapered seat plug, tighten the plug to specifications provided by the vehicle or plug manufacturer. 8. Apply a small amount of silicone dielectric compound to the end of the spark plug lead or inside the spark plug boot to prevent sticking, then install the boot to the spark plug and push until it clicks into place. The click may be felt or heard, then gently pull back on the boot to assure proper contact. 9. INSPECTION & GAPPING Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%. Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag. NEVER adjust the gap on a used platinum type spark plug. Always check the gap on new plugs as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If youre in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldnt go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely never attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it. HOW TO USE THIS BOOK 82 INSPECTION & GAPPING
Checking the spark plug gap with a feeler gauge Adjusting the spark plug gap HOW TO USE THIS BOOK INSPECTION & GAPPING 83
If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs HOW TO USE THIS BOOK 84 INSPECTION & GAPPING
Inspect the spark plug to determine engine running conditions Click to enlarge Spark Plug Wires REMOVAL & INSTALLATION HOW TO USE THIS BOOK Spark Plug Wires 85
Using a spark plug wire removal tool Click to enlarge When removing spark plug wires, use great care. Grasp and twist the insulator back and forth on the spark plug to free the insulator. Do not pull on the wire directly as it may become separated from the connector inside the insulator. To install: Whenever a high tension wire is removed for any reason form a spark plug, coil or distributor terminal housing, silicone grease must be applied to the boot before it is reconnected. Using a small clean tool, coat the entire interior surface of the boot with Ford silicone grease D7AZ 19A331-A or equivalent. Install each wire in or on the proper terminal of the coil pack or distributor cap. Be sure the terminal connector inside the insulator is fully seated. The No. 1 terminal is identified on the cap. 1. Remove wire separators from old wire set and install them on new set in approximately same position. 2. Connect wires to proper spark plugs. Be certain all wires are fully seated on terminals. 3. TESTING Only test one spark plug wire at a time. When the check is complete return the plug wire to its original location. If the wire is defective and more wires are to be checked, mark the wire as such, return it to its original location, then inspect the other wires. Once all of the wires are checked, replace the defective wires one at a time. This will avoid any mix-ups. With Distributor HOW TO USE THIS BOOK 86 REMOVAL & INSTALLATION