Ignition system

Ignition System

Parts in EPC related to ignition system.

This page covers W220 petrol engines M112 (V6 engine used in S350) and M113 (V8 engine used in S430 and S500).

The W220 uses a twin-spark ignition system for each cylinder and thus the V8 has eight ignition coils (or ignition plug packs). There is one coil pack per cylinder, which produces spark for two spark plugs per cylinder.

Misfiring frequently occurs because of burnt ignition coils, faulty ignition cables and spark plugs. These elements have to be replaced regularly.

In case of failure, the following codes can be thrown:

• P2050 Misfiring, Damages TWC (P0300) STORED
• P2056 Misfiring of cylinder 4, damages TWC (P0304) STORED
• P205B Misfiring of cylinder 8, damages TWC (P0308) STORED

Notes on avoiding damage to ignition system

The main points:

• No tests such as holding an ignition HT Wire at a distance from ground and observing a spark must be performed.
• Do not operate the ignition system at starting speed unless all of the HT Wires are connected.
• Before working at cranking speed e.g. to check compression pressure, switch off ignition and disconnect Ignition Control Unit from 12V.

Notes on avoiding damage to ignition system:

• To avoid damage to control unit, only connect and disconnect the two connectors on control unit when ignition is switched off.
• Terminal 1 of ignition coils must not be short-circuited to GND, e.g. as antitheft protection.
• Only install original ignition system components.
• Do not operate ignition system at starting speed unless all of the ignition cables are connected.
• No tests such as holding ignition cable 4 at a distance to GND, unplugging a spark plug connector or pulling cable 4 out of the ignition coils, may be performed at starting speed or when the engine is running.
• Every high voltage circuit must be loaded with at least 2 kΩ (spark-plug connector).
• If it is necessary to test the ignition spark when providing roadside assistance, this must only be done with a spark plug at a cylinder ignition cable. Ensure that spark plug has good contact to ground.
• Before working at cranking speed, e.g. checking compression pressure, switch off ignition and disconnect connector "2" from control unit.

Use of testers and testing units:

• Only connect and disconnect secondary measuring sensor to corresponding ignition cables when vertical engine and ignition are switched off.
• If the short-circuit protection is operated (cylinder comparison) and the engine stays upright, it is not possible to conduct the test with this test instrument.
• Do not connect test lamp to ignition coil terminals 1 and 15.

Remove/install ignition coils

Shown on engine 112 5/1 - Spark plug connector 5/3 - Screw T1/1 - Cylinder 1 ignition coil T1/2 - Cylinder 2 ignition coil T1/3 - Cylinder 3 ignition coil T1/4 - Cylinder 4 ignition coil T1/5 - Cylinder 5 ignition coil T1/6 - Cylinder 6 ignition coil T1/7 - Cylinder 7 ignition coil T1/8 - Cylinder 8 ignition coil Arrow: Identification of the connector

1. Unclip cover on front side of engine
2. Remove engine cover with integrated air filter. The air filter is integrated in the engine cover. Remove the engine cover or the air filter housing by pulling it from the cylinder head covers vertically in the upward direction.
3. Remove air filter housing.
4. Remove screw (5/3). Remove Torx 30 bolts that hold down the coil packs on the valve cover. One T30 bolt per ignition coil.
5. Detach spark plug connector (5/1) from the spark plugs. Pry off spark plug connector (5/1) using open-end wrench, double over the cylinder head cover of the spark plugs. Installation: Observe the identification of the connector (arrow) on the cylinder head cover and the ignition coil of cylinders 1 to 6 or 1 to 8 for the corresponding spark plug connector (5/1). Installing: put pressure on the ignition cable connector to push it all the way on the plug. Listen for a click as it goes on properly.
6. Separate electrical connector of ignition coil of cylinder 1 to 6 (T1/1 to T1/6) or 1 to 8 (T1/1 to T1/8). Installation: Install new cable ties.
7. Remove ignition coil of cylinder 1 to 6 (T1/1 to T1/6) or 1 to 8 (T1/1 to T1/8)
8. Install in the reverse order

Torque specification:

• Bolt, ignition coil to cylinder head cover (Engine 112, 113): 8 Nm

A special spark plug cable removal tool is available (110 589 01 01 00). It is a 17mm, open ended tool with a 25mm off-set and is made by JTC with part number J-1308. It can be found in eBay for $20.

Open-end wrench, double (110 589 01 01 00)

JTC Spark Plug Wire Removal Tool J-1308.

Replace spark plugs

Shown on engine 112 in model 210 01 - Spark plug wrench 1 - Spark plug

Shown on ignition coil of engine 157.980 2 - Spark plug connector 3 - Rubber lip

1. Put hood in service position. Push on the locks on the hinges at left side and then the right side and raise hood to the service position (90 degrees fully open).
2. Remove ignition coils. Keep in correct order as the wire lengths are all different. Do not mix them up (mark with masking tape).
3. Blow out any dirt residue in the spark-plug recesses using compressed air
4. Remove spark plugs (1) using spark plug wrench (01) from cylinder heads. Use an air ratchet with a swivel extension and a 3/8" drive 5/8" spark plug socket.
5. Screw new spark plugs (1) using spark plug wrench (01) into cylinder heads. Start screwing new spark plugs by hand to avoid cross threading.
6. Check spark plug connector (2), ignition coils and ignition lines for damage, deformation and crack formation.
7. Grease rubber lips (3) of spark plug connectors (2) with spark plug connector grease (A0029898051) before installing
8. Install ignition coils

Always remove spark plugs on a stone cold engine or else risking stripping the threads.

Torque specifications:

• Spark plugs (engine 112 and 113): 28 Nm

Cable length symbol on ignition cable connectors.

The valve cover has ignition coil and ignition cable annotations for each cylinder (cylinder 5 H-cable goes to a and G-cable goes to b).

Parts for ignition coil, ignition wire and spark plug replacement job

Swivel extension and spark plug socket. A regular 5/8" (15.8mm) spark plug socket with a rubber insert works well for removing spark plugs. However the secret is to use a variety of extensions e.g., a short 74mm 3/8" drive extension on the tight spots in conjunction with a with swivel head.

In practice, spark plug jobs on M112 and M113 can be done by using pliers with bent nose for ignition plug removal and swivel wrench with short extension and spark plug socket

Swivel wrench with extension and spark plug socket in action (on M113)

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Spark plug connector grease

The rubber boot on the ignition cable is difficult to remove from a spark plug even when using the special removal tool. Solution is to apply a small quantity of dielectric grease to the top conductor and the ceramic insulator (or to the spark plug connector) when re-installing new plugs. This helps keep moisture away and stops corrosion. Makes it infinitely easier to remove the spark plug connector.

• OE - A0029898051 (12 EUR)
• BERU ZKF01 - 0890300029 (8 EUR)
• Permatex 22058

Grease for spark plug adaptors (0029898051)

BERU ZKF01 grease for spark plug adaptors

BERU ZKF01 grease for spark plug adaptors

Permatex 22058 Dielectric Tune-Up Grease

Parts

Spark plugs

• Mercedes-Benz specifies replacement of plugs at every 100 000km or 4 years. Spark plug ignition cables don't last much longer than that either.
• The resistance of the spark plug (electrode to ignition cable connector) is about 4.5K to 6K ohms.
• There should be extremely high resistance between the electrode and the plug metal thread.
• The spark plug electrode gap is 0.039” or 1mm.
• Tightening torque for spark plugs is 20-30 Nm (28 Nm according to WIS).
• Old spark plugs can show worn electrodes and a wider than specification gap.
• Broken insulators are common during removal of seized OEM plugs.
• Corroded spark plug threads make it difficult to remove an old plug. Solution is to use high temperature anti-seize grease (see below) when re-installing new plugs.

Part numbers:

• OE - A0041591903
• OE - A0031599403
• OE - A0041595003 (15 EUR)
• Bosch 0242230500 (5 EUR)
• Denso PK16PRL11 (6 EUR)
• Denso IK16TT (8 EUR) - recommended for LPG, up to 100 0000 km
• NGK 4292 (EUR 8)
• BRISK DR17YS-9 (EUR 3) - suited for LPG, interval max 30 000 km

BOSCH 0242230500

Ignition coils

• It is possible to perform basic tests on an ignition coil using a digital multi meter (DMM). Each coil secondary resistance measured from the plug cable to any of the three pins in the input electrical connector is approximately 4.8 M Ω (Mega Ohms). The cable circuit is isolated from ground thus the resistance between the cable pin and ground is infinity Ohms or open circuit.
• For BOSCH ignition coils the production date is visible on the coil (21T008 means production year 2021).

Parts:

• OE A0001587303 (replaced by A0001587803).
• BOSCH 0221503035 (40 EUR)

Ignition coil (A0001587803)

T30 screw for attaching ignition coil to engine (A0019907212).

Ignition cables

• Spark plug ignition cables have a limited life. The resistance element in the cables often fails or goes high resistance due to fatigue.

Cable lead insulation can break down causing arcing to ground. The resistance for new plug wire is approximately 2.18K ohms.

• It is possible to perform basic tests on an ignition coil using a digital multi meter (DMM). Each coil secondary resistance measured from the plug cable to any of the three pins in the input electrical connector is approximately 4.8 M Ω (Mega Ohms). The cable circuit is isolated from ground thus the resistance between the cable pin and ground is infinity Ohms or open circuit.

Ignition cables are in different lengths:

• G-cable: 245mm - A1121500118 (45 EUR), BOSCH 0356912948 (14 EUR) - M112 x8, M113 x9 (If G-cable is not available, a slightly longer K-cable can be used instead.)
• K-cable: 265mm - A1121500218 (45 EUR), BOSCH 0356912950 (14 EUR) - M112 x4, M113 x4
• H-cable: 290mm - A1121500318 (56 EUR), BOSCH 0356912952 (30 EUR) - M112 x0, M113 x2 (If H-cable is not available, a slightly longer L-cable can be used instead.)
• L-cable: 315mm - A1121500418 (56 EUR), BOSCH 0356912954 (32 EUR) - M112 x0, M113 x1

Ignition cable.

BOSCH spark plug wire set for M113.

Ignition cable lengths for M112 (V6 S350):

• Cylinder 1, port a; K-cable
• Cylinder 1, port b; G-cable
• Cylinder 2, port a; G-cable
• Cylinder 2, port b; G-cable
• Cylinder 3, port a; G-cable
• Cylinder 3, port b; K-cable
• Cylinder 4, port a; K-cable
• Cylinder 4, port b; G-cable
• Cylinder 5, port a; G-cable
• Cylinder 5, port b; G-cable
• Cylinder 6, port a; G-cable
• Cylinder 6, port b; K-cable

Ignition cable lengths for M113 (V8 S430 and S500):

• Cylinder 1, port a; L-cable
• Cylinder 1, port b; G-cable
• Cylinder 2, port a; H-cable
• Cylinder 2, port b; G-cable
• Cylinder 3, port a; K-cable
• Cylinder 3, port b; G-cable
• Cylinder 4, port a; K-cable
• Cylinder 4, port b; G-cable
• Cylinder 5, port a; H-cable
• Cylinder 5, port b; G-cable
• Cylinder 6, port a; K-cable
• Cylinder 6, port b; G-cable
• Cylinder 7, port a; G-cable
• Cylinder 7, port b; G-cable
• Cylinder 8, port a; G-cable
• Cylinder 8, port b; K-cable

Cable kits:

• Valeo 346141 (130 EUR)- M112
• NGK 7800 (221 EUR) - M113
• MAGNETI MARELLI 941318111285 (80 EUR) - M113