The Ford F-150 began its life as just a gap-filler between the F-100 and F-250 pickups in 1975. The 2004 F-150 had two available engines, a 4.6-liter V-8 and a 5.4-liter V-8. Both engines used a distributorless, coil-on-plug ignition system. Instead of having coils that deliver a high-voltage current to multiple spark plugs each, the 2004 F-150's ignition has a coil pack directly attached to each spark plug. On the F-150's engines, a tune-up includes replacing just the spark plugs and the air filter, if needed. Ford recommended replacing the 2004 F-150's spark plugs every 100,000 miles, and the air filter every 30,000 miles.
Check the gap on the eight new spark plugs with a spark plug gap tool. The 4.6-liter engine requires a gap from 0.052 to 0.056 inches. Replace any incorrectly gapped plugs for new ones, as the plugs are not adjustable.
Locate the coil packs on top of the engine, just above the valve covers. Unplug the coil pack wiring harness by pressing the locking button and pulling the harness from the coil pack.
Remove the coil pack-retaining bolt with a ratchet and socket. On 4.6-liter-equipped F-150s, twist the coil pack about a quarter turn to clear the fuel rail. Pull the coil pack upward with a slight twisting motion to remove it.
Remove the old spark plug using a ratchet, spark plug socket and 6-inch extension. Pull the old spark plug from the spark plug socket and insert a new spark plug into the socket.
Hand-tighten the spark plug into the engine with the spark plug socket and a 6-inch extension. Attach a torque wrench to the extension and spark plug socket and tighten the spark plug to 13 foot-pounds on the 4.6-liter, and 25 foot-pounds on the 5.4-liter engine.
Coat the inside of the coil pack's boot with dielectric grease and position the coil pack on the spark plug. Press downward until the coil clicks into place on the plug. Twist the coil pack until the bolt hole in the coil lines up with hole in the engine.
Reinstall the coil pack-retaining bolt and tighten it to 4 to 5 foot-pounds with a torque wrench and socket. Plug the wiring harness back into the top of the coil pack.
Repeat Steps 2 through 7 to replace the remaining seven spark plugs.
Unfasten the clamp on the air filter box -- on the front, left of the engine compartment -- by lifting up on the clasp.
Pull the engine side air filter box toward the passenger's side of the truck to until it is clear of the lip on the other half of the air filter box. Position the engine side of the air filter box aside.
Pull the air filter from the air filter box. Insert a new air filter into the air filter box in the same position the old filter was in.
Reinstall the engine side of the air filter box and verify that the two halves of the air filter box did not pinch the air filter.
Position the clamp so that both halves of the air filter box are inside the clamp and press the clasp to lock it in place.
Release the two air filter tray retaining clamps -- located on top of the engine -- by pulling upward on the clamps.
Slide the air filer tray out of the air filter box. Make note of the air filters position on the tray and pull the air filter from the tray.
Install a new air filter in the tray in the same position the old filter was in.
Slide the air filter tray back into the air filter box.
Reposition the clasps so they are back on the air filter box. Lock the clasps by pressing them downward to lock the air filter tray in place.
