Hi, planning replace my sparkplugs. Looks like I need to unplug and move the ECU - should I unplug the battery before doing this? Anything else I should know?

Thanks!

 

It's not that easy a job on the M276 engine which normally involves removing the intake manifold which is why dealers charge $600+ to do it, but if you search, there are threads where people said they did it without removing the intake but overall it's not a simple job like it is on an M272 engine.

 

yes, before unplugging ECU please disconnect battery cable, the negative one is enough.

 

With small hands and the right pick tool and boot puller, you won't need to remove the intake manifold and yes, disconnect the battery first.

 

No, battery disconnection is not required. I have changed plugs twice with this method. WIS does not call for battery disconnection. Read the DIY in my signature, WIS for W166/M276 is provided.

Senior Leigh on YouTube has an M276/W212 spark plug video.

Intake manifold removal is not required

 

Good luck. Prepare to replace some of the plug wires as they can be very difficult to remove without breaking or twisting. Chassis is correct, intake doesn't need to be removed.

 

Do it once do it right... the No1 cause of repeat plug job is misfires, right?
You can save your good coils but change the "rubber boots" and grease them with dielectric silicone.

BATT OUT:
I side with disconnecting the battery regularly plus anytime you work on modules. The ECU may act quiet with engine off but it's watching bus signals.

No Problem:
Ghosting modules is a easy way to waste time later chasing odd errors later.
Besides rebooting these cars is excellent medicine for SAM glitched by poor GND and PWM spikes.

Shop vs. DIY:
Shops want many quick easy jobs - Remotely following WIS procedures and expertly cutting corners are proven ways to earn a keep.

DIY want quality experience - Many unwritten details make the difference between good and better procedures.

Replacing the plug boots prevent zapping the coils secondary winding insulation when 30kV sparks have nowhere to find GND, a path gets made and misfire created.

Everyone sees things differently, some people want quicker some want better - We are all distinctly right in light of priorities.

 

I disconnected the battery even though you don't technically have to because working with ratchets, extensions and sockets, the last thing I want is closing a circuit with me in it. I'll admit in the past I was lazy and covered the positive post but it's just as quick to disconnect the neg and I go even further by covering it with a glove or towel.

 

This past weekend I changed the plugs in my wife's 2018 GLE 350, which shares the same M276 engine. I did not disconnect the battery and all went fine. The radiator fan did spin up when I reconnected the ECU, but had read that was normal so it was expected. I will probably disconnect it in the future for added insurance.

Some things I learned:

• Those little grey clips that lock the connector onto coils break easily. I went super slow but still managed to break 2 out of 6 and I'm crossing my fingers they stay put without them. I would find it hard to believe the dealer guys could do any better because I've seen their work and stopped bringing my car there. It's one thing to pay top dollar for top quality work, but not for sub-par work. My car has only gone to the dealer three times and each time I later found tools or parts left under the hood. But that's a story for another time.
• The coil connectors were unreasonably stuck in place. It sometimes seemed to help to push them further on before trying to push off.
• The curved "boot" pliers didn't seem to be super helpful to me in the traditional manner. Maybe mine were too thick but there wasn't much room to maneuver them and grab the boot around the plastic cover and I didn't want to pull from just the rubber part. Instead I used the pliers to lever underneath the flat spot. This was very effective but does require quite a bit of force. I put a dab of dielectric grease inside each and they slid in almost too easy. It must be that the original grease turns to glue because it's unbelievable the difference before and after.
• Be sure to have a magnetic pick up tool handy, this was my favorite tool of the job as I inevitably dropped bolts or tools.

It was a nice day so I decided to also change the plugs on my daughter's Subaru Crosstrek and the M276 almost seemed easy in comparison. There is very little room between the coils and frame rails on those cars and it was very difficult to get tools in there. On top of that the coil bolts and spark plugs were in super tight. The service instructions state to loosen the engine mounts and raise the engine but it is possible to do without doing that. At least the coil boots came out easily and I didn't even bother to disconnect the wires as there was enough length to work with.

 

I have done it twice: my W212 and sister's W166. Compared to the M272 (which I also did), it is more laborious, but not rocket science.

Here is my summary:

1 - Definitely no need to remove the intake manifold as mentioned by others. But be patient with the one near the driver's side firewall, and the one close to the ECU. I did not disconnect the battery, but both times the radiator fan came up when I reconnected the ECU (as mentioned by @up_too_late ). If I were to do it again, I will disconnect the battery.
2 - I followed the video from Senior Leigh, sorry @chassis I had not seen your detailed explanation earlier. I also removed the bolt after removing the ECU
3 - On the gray locking parts, I did break one , but I bought the connector (@$2+) at the dealer (need to find the receipt for the part number) and transplanted the lock. I did not want to mess with replacing the connector.
4 - Do get a spark plug socket with a magnet, and a swivel extension. . For your own good, do NOT use a standard spark plug socket w/o the swivel extension (6" minimum) on the plug next to the firewall, if it gets stuck pulling it out, and it separates from the extension, there is no vocabulary to match the PITA that it takes to get it out.. Also, I got the one on the link earlier, but I also got a shorter extension (6") in my toolbox now. The shorter one is a lot more versatile though.
5 - Do definitely use dielectric silicone as @CaliBenzDriver suggested, I used
6 - Be careful with the bolts on the coils (aluminium), you do not want to over-tight them or you will have a nasty gift in your hands. Same if you feel like moving the oil dipstick tube.
7 - You can use a boot puller such as , or create your own with a string cord. Be careful not to pull too fast/hard and damage the coil-boot.

Here is the link to Senior Leigh procedure

 

Thanks this is really helpful!!!

 

I've done plugs on the Crosstrek and having basically no room with the frame rail there was indeed a PITA. Had to get real creative with extensions and swivels.

 

Great to know the grey locks are replaceable!

I used a thin walled spark plug socket from FCP Euro and it did get stuck on the first plug I put in, but I had started with the easiest one which is the passenger side closest to the front so I was able to pull it out with pliers. After that I took the old spark plug and smeared some dielectric grease on the porcelain and inserted it into the socket. That lubricated the o-ring inside the socket just enough so that it would still grip the spark plug but not so much it would cause the extension to disconnect. You don't need much grabbing force to extract the spark plug.

 

You mean you don't tape the extension to the socket?

 

The gray locks are not needed, typical German over-engineering, as if your car were a rocketship flying to the moon, with no room for error. I pull the grey locks out (they break anyways) and throw them away. Replaced well over 50 sets of these plugs. Never had a problem afterwards.

 

This has been a great thread since I have to take care of my plugs soon and got quoted 800 by an independent mechanic. Thanks you guys for all the great advice and info..

Are there any other tools or things you guys recommend? I have a bunch of tools from past cars, but finding these germans have me increasing my speciality tools in my toolbox

 

You need to shop around more, the dealers charge $600 and they usually have some minor discounts. The indys are supposed to be cheaper than the dealer, not more.

You could also get the pre-paid maintenance package and that should cover the spark plugs if they're due. I think you can get them up to 80k on the mileage and they cover the spark plugs and transmission fluid if they're due.

 

I would say the keyword here is TORX, if you do not have them do not even touch your MB. Now, which ones? I would say that these german engineers will find use for any available contraption TORX exist out there. When it is not the size of the bit/socket, is the depth/length. Always need the one you do not have.

Here is a picture from Amazon (I do not own this set, nor promote it)

 

I picked up a flex head 3/8" ratchet with a long handle, not mandatory but certainly helpful.