How to Install Spark Plugs on a 1999 Ford F-150

One of the focuses Ford always had with the F-150 was to give buyers as many options as possible to fulfill their automotive needs. The 1999 F-150 is no exception to this tradition, as it had three engine sizes from which to choose. The entry-level engine was a 4.2-liter V-6, the next step was a 4.6-liter V-8 and the largest engine was a 5.4-liter V-8. Replacing the spark plugs on all three engines is a relatively simple task that most do-it-yourself mechanics can perform.

Instructions

Check the gap between the electrodes on the bottom of the new spark plugs with a spark plug gap tool. The correct gap for these plugs is 0.052 to 0.056 inches. Adjust any incorrectly gapped plugs for the 4.2-liter by widening or narrowing the gap between the electrodes with the spark plug gap tool. Replace any incorrectly gapped plugs for the 4.6-liter with new ones, as they are platinum and are not adjustable.

Trace one spark plug wire to the side of the engine until you reach the thick, rubber boot on the end of the wire that connects the wire to the spark plug. Pull upward on the boot with a slight twisting motion to remove it from the spark plug.

Remove the spark plug with a ratchet and spark plug socket. Hand-thread a new spark plug into the vacant hole, feeling for any resistance as you thread it. If you feel resistance, immediately remove the plug and re-thread it into the engine. Tighten the spark plug to between 7 and 15 foot-pounds with a torque wrench and spark plug socket.

Inspect the entire spark plug wire for any defects, including cracks, splits, brittleness, burn marks or excessive age. If any defects exist, replace all of the spark plug wires one by one. Replacing them one by one prevents mixing up the firing order.

Apply a dab of dielectric grease meeting Ford specification ESE-M1C171-A to the inside of the spark plug wire boot and spread it around with a small flat-head screwdriver. Align the spark plug wire boot with the top of the spark plug and press the boot onto the plug until you feel it click.

Repeat steps 2 through 5 to replace the remaining five spark plugs on the 4.2-liter engine and seven spark plugs on the 4.6-liter engine.

Check the gap on all eight new Motorcraft AWSF-12E or equivalent spark plugs, following the process laid out in Step 1 of the previous section. Do not adjust these plugs, as any incorrectly gapped plugs require replacement.

Press and hold the unlocking button on the fuel injector wiring harnesses blocking the passengers front ignition coil pack and pull the harness from its injector. Press and hold the unlocking button on the ignition coil packs wiring harness and unplug it from the coil pack.

Remove the coil pack bolt with a ratchet and socket and pull upward on the coil pack with a slight twisting motion to remove it, exposing the spark plug under it.

Remove the spark plug with a ratchet, 3-inch extension and spark plug socket. Pull the spark plug from the spark plug socket and press a new one into the socket. Hand-thread the spark plug into the engine with the spark plug socket and feel for any resistance as you thread it in. Remove the spark plug and re-thread it if you feel resistance.

Tighten the spark plug to 11 foot-pounds with a torque wrench, 3-inch extension and spark plug socket.

Squeeze a small amount of dielectric grease meeting Ford specification ESE-M1C171-A into the rubber boot on the bottom of the coil pack. Spread the grease around the inside of the boot with a small flat-head screwdriver.

Align the bottom of the coil packs boot with the top of the spark plug, then press it onto the plug until you feel it click into place. Hand-thread the coil pack bolt, then tighten it to 6 foot-pounds with a torque wrench and socket.

Plug the wiring harness into the coil packs receptacle and press the fuel-injector wiring harness into the fuel injectors receptacle.

Repeat steps 2 through 8 to replace the remaining seven spark plugs.