1991 1999 ford explorer chilton User Manual

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...

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...

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...

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...

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,...

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...

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,...