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Spark Plugs Ignition Wires Coils Replacement
 
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Pelican Technical Article:

Spark Plugs Ignition Wires Coils Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$150

Talent:

***

Tools:

T30 Torx, 5/8 spark plug socket, torque wrench

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Spark plugs, ignitions coils, ignition wire set

Hot Tip:

Work with a cool engine

Performance Gain:

Engine runs well

Complementary Modification:

Replace ignition wires

An engine running at 2000rpm cruising down the road means the spark plug has high energy ignition voltage arcing across the spark plug gap 1500 times per minute on a 6 cycle engine. Every time an electric current arcs across two metal surfaces 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.

Replacing the spark plugs on your W211 is part of routine maintenance. Mercedes-Benz recommends replacing the spark plugs on 6-cylinder models every 100,000 miles or every 5 years. With all the major engine design changes over the years, spark plugs now last up to three times as long as they did in years past. This is good and bad. It means you save money and time not having to service them so frequently, but run the risk of a spark plug seizing in the cylinder head. I suggest replacing your spark plugs every three years regardless of mileage. If the last time they were serviced is unknown, replace them right away.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

When servicing your spark plugs be sure the engine is cool and leave yourself about an hour to do the job. Be careful not to drop a spark plug. If you do, replace it. The spark plug insulator can crack and can lead to an engine misfire.

Working at the engine cover (red arrow), pull off the two front sir duct hoses (green arrows).
Figure 1

Working at the engine cover (red arrow), pull off the two front sir duct hoses (green arrows).

To detach the ducts, pull them straight off the engine cover / air filter housing.
Figure 2

To detach the ducts, pull them straight off the engine cover / air filter housing. Then pull the front of the duct out of the radiator support and remove it from the engine. Repeat this step for each duct.

Lift up and remove the front engine cover.
Figure 3

Lift up and remove the front engine cover.

Then, pull the engine cover / air filter housing straight up to remove it.
Figure 4

Then, pull the engine cover / air filter housing straight up to remove it. The cover is held on by four metal clips that grab onto rubber mounts, with the front two shown (red arrows). The rear of the cover has two as well. Once detached, remove the engine cover / air filter housing from the engine.

W211 models with a 6-cylinder engine utilize one ignition coil per cylinder (green arrows).
Figure 5

W211 models with a 6-cylinder engine utilize one ignition coil per cylinder (green arrows).

Each ignition coil (green arrow) has two ignition wires running to spark plugs (red arrows).
Figure 6

Each ignition coil (green arrow) has two ignition wires running to spark plugs (red arrows).

Using spark plug wire pliers, remove the spark plug wires from the spark plugs.
Figure 7

Using spark plug wire pliers, remove the spark plug wires from the spark plugs.

If replacing the wires, use the spark plug pliers to remove the connection at the ignition coil as well.
Figure 8

If replacing the wires, use the spark plug pliers to remove the connection at the ignition coil as well. When installing new wires, the upper coil connection connects to the front most plug for that cylinder. The lower coil connections connects to the rear most plug for that cylinder. See the ignition coils steps below for more information.

Using a 5/8-inch spark plug socket on a swivel extension, remove the spark plug from cylinder head.
Figure 9

Using a 5/8-inch spark plug socket on a swivel extension, remove the spark plug from cylinder head. 

Remove the spark plug from the cylinder head.
Figure 10

Remove the spark plug from the cylinder head. Remove all other spark plugs. There are 12 in total. Lightly lubricate the new spark plugs with copper based anti-seize. Thread the spark plugs into the cylinder head by hand. This will prevent accidental cross-threading. Torque the spark plugs to 25 Nm. Be sure to route the ignition wire as it was before. Install the engine covers and check your work.

To replace an ignition coil, disconnect the electrical connector by pressing the release tab and pulling it straight off.
Figure 11

To replace an ignition coil, disconnect the electrical connector by pressing the release tab and pulling it straight off.

Then, remove the T30 Torx fastener (red arrow).
Figure 12

Then, remove the T30 Torx fastener (red arrow). If needed, cut the zip tie securing the wiring harness to the coil.

This photo shows the coil fastener being removed.
Figure 13

This photo shows the coil fastener being removed.

Lift the coil straight up to remove it.
Figure 14

Lift the coil straight up to remove it.

If you suspect a coil is faulty, you can swap the coils and wires to a different cylinder.
Figure 15

If you suspect a coil is faulty, you can swap the coils and wires to a different cylinder. If the problem follows the coil you moved, replace the coils or wires.

This photo shows the first spark plug on the right side of the engine (cylinder 1).
Figure 16

This photo shows the first spark plug on the right side of the engine (cylinder 1). This is where the top wire on the first coil attaches. Note the spark plug location during the procedure. Plugs side by side are not for the same cylinder.

This photo shows the second and third spark plugs on the right side of the engine (cylinder 1 second plug and cylinder 2 first plug).
Figure 17

This photo shows the second and third spark plugs on the right side of the engine (cylinder 1 second plug and cylinder 2 first plug). Note the spark plug location during the procedure. Plugs side by side are not for the same cylinder.

Each coil has numbers and letters.
Figure 18

Each coil has numbers and letters. Use the letters on the coil and the markings on the valve cover to route new wires. The A on the coil coincides with the A on the valve cover. A is for the top ignition coil wire. B is for the lower ignition coil wire.


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