Replacing spark plus is regular maintenance. There is a requirement every 60k miles or 6 years to replace the spark plugs in the MB maintenance booklet. To naturally aspirated engine of M276 DE35, there is a step to remove the resonance intake manifold to reach the ignition coil in the WIS. But that must replace a set of expensive intake plenum gaskets with more labor. Removing the ECU may make more room to reach the concealed ignition coil and spark plugs. More detail below.
Parts & Accessories
Replace Spark Plugs of 4th, 5th & 6th Cylinder
Step 1 Open The Engine Hood
1.1 Pull lever on left side of the footwell to unlock the engine hood. The engine hood jumps open; lift engine hood slightly if necessary;
1.2 Pull out handle and lift to open engine hood. (Windshield wiper arms must not be folded forward).
Step 2 Remove ECU (Important Step)
2.1 Remove front engine cover;
2.2 Remove electric connecter from ECU;
2.3 Remove ECU;
2.4 Remove wire harness from resonance intake manifold;
2.5 Unscrew the bracket of electric wire harness.
Step 3 Remove the Used Spark Plug of 6th Cylinder (The Most difficult One)
3.1 Detach connector of ignition coil;
3.2 Remove bolt of ignition coil;
3.3 Pull ignition coil upwards and remove;
3.4 Remove spark plug.
Step 4 Install the New Spark Plus of 6th Cylinder
4.1 Install new spark plug with 23Nm (204 Ib-in);
4.2 Apply dielectric grease on the lip of spark plug connector;
4.3 Install ignition coil with 9Nm (80 Ib-in) on bolts;
4.4 Install connector to ignition coil with dielectric grease;
4.5 Connect the wire harness to intake manifold.
Step 5 Replace the Spark Plug of 4th, 5th Cylinder
5.1 Replace spark plugs of 4th, 5th cylinder same with step 3-4;
5.2 Install ECU with the reverse of step 2.
Replace the Spark Plugs of 1st, 2nd & 3rd Cylinder
Step 6 Remove Air Filter Housing
6.1 Detach the connector of the airflow sensor;
6.2 Unscrew two bolts for air filter housing;
6.3 Loosen the clamp for intake hose;
6.4 Remove air filter housing.