I have a 2005 C230 kompressor (W203, M271 engine). I changed the spark plugs this weekend. Disclaimer: I am a lawyer, not a mechanic. This is for information purposes only. You should have auto maintenance done by trained and experienced professionals. You could injure or kill yourself and/or destroy your car and tools if you work on it yourself. I’m not responsible for any of that. Other models or years may be totally different. This is what I used.
Â¼” ratchet and sockets
nutdriver that uses Â¼” sockets
3/8” ratchet, extensions
5/8” spark plug socket
E8 star socket ($20 star socket set at Autozone)
4 new Bosch spark plugs, FR6332 per spec in manual (ordered from Amazon, $40 shipped. Few auto parts stores will have this plug in stock)
torque wrench (18.5 ft. lbs. included in range)
These are the steps I followed.
1. Wait until engine is cold. You don’t want to burn yourself on hot parts.
2. Disconnect negative battery cable. It is grounded near the battery on a stud and nut. Anytime working on anything electrical, do this first. Be careful not to drop the nut. I did and had to use a flashlight and magnetic pick up to fish it out from where it fell into a gap by the battery.
3. Remove plastic engine cover. It just pulls off at the corners.
4. You will see the coils. The M271 uses coil on plug ignition. There is one coil per plug and no spark plug wires or distributor. If there is dirt or grime, blow it off with compressed air or clean it off. You don’t want anything to fall into cylinder because it could mean a new engine. On my car, it was clean enough to eat under the cover. Thanks, cover.
5. Pinch both wiring harness tabs where harness connects to coil and unplug harness connector.
6. The coil is held on by 2 long bolts with E8 star heads. Use Â¼” ratchet and E8 star socket to remove these. I had to buy the star sockets set at Autozone. I have worked on various German and Japanese cars for years and this is the first time I needed star sockets.
7. Here you see the plug at the bottom of the spark plug well.
9. Use ratchet, extensions and 5/8” spark plug socket to remove spark plug. It should stay in the socket.
10. Get the new plug ready. Put a thin coat of high temp anti seize paste on the threads only. Plugs are pregapped to correct gap so I didn't worry about setting the gap.
11. Put new plug in the spark plug socket. Using the extension (NO ratchet yet) hand thread the plug in hand tight. Always start it by hand to avoid cross threading. Unless you want to spend thousands at the dealer to have a helicoil insert put in when you cross thread. When you have it hand tight and are 100% sure you didn’t cross thread, use torque wrench to tighten to 18.5 ft. lbs. Don't overtighten or you could be paying thousands to the dealer again.
12. Put coil on top of plug. Make sure it is seated. Put the 2 star bolts back in and tighten them down. These are small bolts and don’t require much torque at all. I used a nutdriver to start it and then a little pressure on the Â¼” ratchet. A good mechanic once told me that he always uses 1/4" ratchet unless he is sure torque of a 3/8" or larger is needed. A good way to avoid breaking bolts.
13. Reconnect the harness plug.
14. Repeat for the other 3 cylinders. The only one that was a little harder was no. 3. There is very little room to unplug/plug the harness. I had to loosen part of a harness to get enough clearance.
15. Make sure all harnesses are connected and all coil bolts are tightened. Put cover back on. Reconnect neg. battery cable.
15. Start car to make sure it is working right. Write in your service history book that you changed the plugs. Reset the date and time and anything else that was reset. Make sure you have the radio codes in case it makes you reenter that.
16. I cleaned up the plastic parts of engine a little using Vinylex.