What Are the Steps to Change Spark Plugs on a 1996 Mercedes Benz- S420?

The 1996 Mercedes S420 was equipped with a 4.2-liter V-8 engine that produced 275 horsepower and 295 foot-pounds of torque. The 1996 S420 had a five-speed transmission with automatic overdrive. The engine on the S420 used a coil ignition system, with separate coils above each cylinder. To replace the spark plugs, the coils and some engine parts need to be removed. Spark plugs on the 1996 S420 should be replaced at least every 30,000 miles.

Instructions

1

Open the hood. Remove the ignition coil covers from the top sides of both rocker arm covers, using a Torx bit driver.

2

Disconnect the electrical connector from the top of a single coil. The coils are located in the top of the valve covers. Remove the two mounting screws at the top sides of the coil, using the Torx driver.

3

Pull the coil pack off of the engine by pulling upward with a twisting motion. Remove the spark plug by turning it counterclockwise, using your ratchet, extension and a spark plug socket. Spark plug sockets are designed to grip the spark plug for easier removal and installation of plugs.

4

Set the gap on the new spark plug to 0.032 inch or 0.08 mm, using a spark plug gap tool or feeler gauges. Some spark plugs do not have an adjustable gap, so check gaps and exchange the plugs if the gap is incorrect. Insert the spark plug into the spark plug socket. Separate the ratchet and extension and use only the spark plug socket and extension to start the installation of the new plug. Turn the plug clockwise by hand to ensure no cross-threading of the new plug.

5

Tighten the spark plug between 18 and 21 foot-pounds using a torque wrench. Install the coil onto the new plug with a twisting motion. Insert the two mounting screws onto the coil, and tighten them snug with a Torx hand driver. Connect the electrical connector back onto the coil, by hand.

6

Repeat steps 2 through 5 to complete the spark plug replacement on the entire engine. Install the coil covers back onto the engine and tighten them snugy with the Torx driver.