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Pelican Technical Article:

Spark Plug Removal

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$50

Talent:

*

Tools:

4mm Allen head, spark plug socket with ratchet and extension

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Spark plugs

Hot Tip:

Thread in spark plugs with socket by hand before tightening with ratchet

Performance Gain:

Smoother running engine, reduced emissions, proper fuel economy

Complementary Modification:

Change the spark plug wires if cracked or damaged

An engine running at 2000rpm cruising down the road means the spark plug has high energy ignition voltage arcing across the spark plug gap 1000 times per minute on a 4 cycle engine. Every time an electric current arcs across two metal surface one electrode (anode) loses material and the other electrode (cathode) gains carbon from the arcing. A very small amount of current passes through a spark plug so the arcing is not a problem in the short term. In addition, the explosion of combustion also wears away the spark plug electrodes over time. As the spark plug gap widens the heat generated by the spark becomes weaker and has a harder time igniting the air/fuel mixture. This leads to inefficient combustion which reduces fuel economy, increases emissions and reduces power output. In this tech article we will go over the steps to remove you spark plugs so you can replace them.

Mercedes Benz recommends the spark plugs get replaced every 30,000 miles.

With a large screwdriver, remove the two plastic fasteners that hold down the spark plug cover.
Figure 1

With a large screwdriver, remove the two plastic fasteners that hold down the spark plug cover. ThisPicture shows us on the right side valve cover. Perform this same step on the left side spark plug cover.

Lift the spark plug cover off of the valve cover.
Figure 2

Lift the spark plug cover off of the valve cover. Do this for both the left and the right banks of the engine.

Using your hands or a pair of pliers twist the spark plug wires first then pull them out of the spark plug holes.
Figure 3

Using your hands or a pair of pliers twist the spark plug wires first then pull them out of the spark plug holes. If available, use a pair of spark plug pliers, or wrap the jaws of your pliers with tape to protect the wires.

Use a spark plug socket with an extension and ratchet to remove the spark plug by spinning it counter clockwise.
Figure 4

Use a spark plug socket with an extension and ratchet to remove the spark plug by spinning it counter clockwise.

The spark plug should come out seated in the spark plug socket.
Figure 5

The spark plug should come out seated in the spark plug socket. If not use a magnet to retrieve the spark plug.

Repeat this step for the other seven spark plugs.
Figure 6

Repeat this step for the other seven spark plugs. ThisPicture illustrates only the right side cylinder head. Remove the spark plugs from both cylinder heads.

If you are worried about mixing up the spark plug wires you can do one spark plug at a time.
Figure 7

If you are worried about mixing up the spark plug wires you can do one spark plug at a time. Depending on the brand of wires that are installed on your vehicle the individual plug wires should have a number tab (green arrows) to identify the wires. Installation is the reverse of the removal steps. Install each spark plug and tighten them down being careful not to over-tighten them. Install the spark plug wires down their spark plug holes and push down to make sure they are seated properly. Route the spark plug wires in the valve cover and install the spark plug wire covers. Tighten down the screws that hold them down. Do not over-tighten them, they are plastic and they will break. Start the engine and make sure runs smooth.

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Comments and Suggestions:
Robert Comments: What are the torque specs on the plugs?
August 13, 2016
  Followup from the Pelican Staff:
I don’t have that info.


I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 

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