How to Change the Spark Plugs on a 1999 Mercury Marquisby Justin Cupler
The Grand Marquis had been a part of Mercury’s lineup since 1975. The 2011 model year, however, marked its final year of production. The 1999 Mercury Grand Marquis came standard with a 200-horsepower, 4.6-liter V-8 and had a 215-horsepower version of the 4.6-liter as an option. Both engines used a coil-on-plug ignition system, which places an individual ignition coil on each spark plug. Replacing the spark plugs on both versions of the 4.6-liter is the same straightforward process.
Check the gap on the base of all eight new Motorcraft AWSF-32P, or equivalent, spark plugs with a spark plug gap tool. The correct gap for the Grand Marquis’s 4.6-liter engine is 0.052 to 0.056 inches. Replace any incorrectly gapped spark plugs for new ones, as these plugs are not adjustable.
Remove the retaining screw on the center rear of the engine cover with a Phillips screwdriver and pull the cover off the engine.
Remove the two smaller hoses plugging into the air cleaner outlet hose by pulling each hose away from the air cleaner outlet hose. Loosen the hose clamps securing both ends of the air cleaner outlet hose with a Phillips screwdriver.
Pull both ends of the hose from their connection points and remove the hose from the engine compartment.
Look on the top of the engine, just inward from the valve covers, and find the eight coil packs – four on each side.
Press and hold the locking button on one coil pack's wiring harness and pull the wiring harness from the coil pack. Remove the coil pack retaining bolt with a ratchet and socket. Pull the coil pack upward with a slight twisting motion to remove it.
Blow the spark plug tube out with compressed air to remove any debris surrounding the spark plug. Remove the spark plug with a ratchet, 6-inch extension and spark plug socket.
Pull the spark plug from the spark plug socket – a rubber insert inside the socket holds it in place. Insert a new spark plug into the spark plug socket until the rubber insert holds it in place.
Hand-thread the spark plug into the engine with the spark plug socket and 6-inch extension. Attach a torque wrench to the extension, and tighten the spark plug to 15 foot-pounds.
Squeeze a small amount of dielectric grease inside the coil pack’s rubber boot and spread it around the inside of the boot with a small flat-head screwdriver. Line up the coil pack boot with the top of the new spark plug and press the coil pack onto the spark plug until you feel it click into place.
Line up the coil pack's bolt hole with the bolt hole in the cylinder head. Hand-tighten the coil pack retaining bolt, then tighten it from 7 to 8 foot-pounds with a torque wrench and socket. Plug the wiring harness back into the receptacle on the top of the coil pack.
Repeat Steps 6 through 11 to replace the remaining seven spark plugs.
Press the air cleaner outlet hose ends back onto the air cleaner box and throttle body inlets. Tighten the two hose clamps with a Phillips screwdriver. Plug the two smaller hoses into their respective holes in the air cleaner outlet hose.
Set the engine cover back on top of the engine and tighten its retaining screw with a Phillips screwdriver.