Changing Spark Plugs or Ignition Coils on R172 3.5L V6 (M276 Engine) - Mercedes Benz SLK Forum

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#1 Old 06-11-2015
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Changing Spark Plugs or Ignition Coils on R172 3.5L V6 (M276 Engine)

After a fruitless search on how to change the spark plugs on the M276 V6 engine used on the R172 SLK 350, I decided to just go ahead and try it myself.
After encountering a couple of problems that required several days research I was able to get the spark plugs changed on my 2012 SLK 350.
The biggest problem was removing the ignition coils on the left side of the engine where space is at a premium.

Attached is a document that details the steps involved and the workarounds that I used to complete the task.

All in all the work in involved is not that hard, it's just fiddly.
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File Type: pdf 2012 SLK 350 3.5 V6 (M276 Engine) Spark Plug Replacement.pdf (3.98 MB, 765 views)

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Last edited by WhiteRabbit; 06-11-2015 at 03:36 PM. Reason: gammar
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#2 Old 08-15-2015
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Just wondering? At how many miles did you change out the spark plugs?

Thanks
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#3 Old 08-15-2015
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Originally Posted by Iron Sight View Post
Just wondering? At how many miles did you change out the spark plugs?

Thanks
The mileage was only a little over 16,000 miles at the time and just barely under 4 years of almost daily use.
However, I plan to keep the car for at least several more years.
I wanted to be sure that changing the plugs was something I could do without too much trouble. And it would give me a general idea of the engine's condition.
Also the car's warranty was about to expire and I figured if I screwed something up there was a chance it would be a covered expense - yea I know, wishful thinking on my part.

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#4 Old 01-22-2016
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Signed up so I can download the attached PDF. After reviewing the document, all I can say is THANK YOU. This is exactly what I needed (I have a 2012 C350, but with an M276 engine as well).

My only concern now is the socket for the plugs. I was originally going to get this...Amazon.com: GearWrench 80546 5/8-Inch x 6-Inch Swivel Spark Plug Socket: Home Improvement
...a magnetic spark plug swivel socket, however your comment about using a thin walled socket is having me have doubts.
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#5 Old 01-23-2016
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Originally Posted by edgalang View Post
Signed up so I can download the attached PDF. After reviewing the document, all I can say is THANK YOU. This is exactly what I needed (I have a 2012 C350, but with an M276 engine as well).

My only concern now is the socket for the plugs. I was originally going to get this...Amazon.com: GearWrench 80546 5/8-Inch x 6-Inch Swivel Spark Plug Socket: Home Improvement
...a magnetic spark plug swivel socket, however your comment about using a thin walled socket is having me have doubts.
Glad to be of help.

The spark plug socket you linked to will not work as the spark plug tunnel is very narrow. Also that one is 5/8" and not 14mm as is required.
You need a thin-wall, 14 mm, 12 point spark plug socket.

I used this 3/8” drive 14mm 12 point spark plug socket that I found on eBay:
MINI Spark Plug Socket Thin Wall 3/8" Drive 12 PT Point 14mm FITS BMW MERCEDES
This socket has a clip in it that holds the spark plug better than a magnet would.
There are several other sockets that are the correct size on eBay as well.

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#6 Old 05-22-2016
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First off a big thank you for your write up and detailed info.

I'm having one hell of a time with the wiring sockets on the coil packs. Not sure if anyone else has had similar experience but it feels as if they're going to snap with too much force.

I've changed plugs on older MB's and it's never given this much fight.
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#7 Old 05-22-2016
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Quote:
Originally Posted by Justinqueensny View Post
First off a big thank you for your write up and detailed info.

I'm having one hell of a time with the wiring sockets on the coil packs. Not sure if anyone else has had similar experience but it feels as if they're going to snap with too much force.

I've changed plugs on older MB's and it's never given this much fight.
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#8 Old 05-23-2016
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Originally Posted by Justinqueensny View Post
First off a big thank you for your write up and detailed info.

I'm having one hell of a time with the wiring sockets on the coil packs. Not sure if anyone else has had similar experience but it feels as if they're going to snap with too much force.

I've changed plugs on older MB's and it's never given this much fight.
At first I also had a hard time removing the wiring connectors from the ignition coils. It turned out that I was making it harder than need be.

Here's the easiest way to do it.
As shown in the first image below:
1. Slide the light gray locking tab towards the wiring end of the socket to release the tab lock. It should now look the same as the gray tab does in image #1.
2. Instead of using a screwdriver, use your thumb to push down on the front of the gray tab while at the same time pushing with your thumb towards the wiring end of the socket.
Just when you think the socket will not release push a little harder forward with your thumb and the socket will release from the plug!

If you look around the engine you can see very similar connectors that are easier to get to than the ones on the ignition coils.
Use one of those other ones to practice on.
That way you can get a feel for how it actually should work.

Let us know how you make out.
Attached Images
File Type: jpg Removing Ignition Coil Wiring Socket.jpg (48.6 KB, 69 views)
File Type: jpg Ignition Coil Wiring Socket Removed.jpg (58.4 KB, 48 views)

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Last edited by WhiteRabbit; 05-23-2016 at 11:22 AM. Reason: Cleanup text
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#9 Old 05-26-2016
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Quote:
Originally Posted by WhiteRabbit View Post
Glad to be of help.

The spark plug socket you linked to will not work as the spark plug tunnel is very narrow. Also that one is 5/8" and not 14mm as is required.
You need a thin-wall, 14 mm, 12 point spark plug socket.

I used this 3/8” drive 14mm 12 point spark plug socket that I found on eBay:
MINI Spark Plug Socket Thin Wall 3/8" Drive 12 PT Point 14mm FITS BMW MERCEDES
This socket has a clip in it that holds the spark plug better than a magnet would.
There are several other sockets that are the correct size on eBay as well.

Odd that I didn't get a notification to reply to this thread until now, but since I'm here, I'd like to THANK YOU once again. Your tutorial gave me enough confidence to change spark plugs for the first time on any car!

Here's a few notes of my experience for those who might be in the same situation...

1- I ended up ordering from Amazon since I have Prime and had credits. This is what I used...BMW Magnetic Thin Wall Spark Plug Socket 3/8" Drive 14mm 12 Points - - Amazon.com
...and paired it with this...Amazon.com: TEKTON 4964 Impact Universal Joint Set, Cr-V, 3-Piece: Home Improvement

2- I really really wanted to remove the clamp @ step #8 . By keeping it on and just moving the box, I kinda thrashed the soft heatshield that is attached to the back of the airbox since it kept sliding down. I even had a "Clic / Clic-R Collar Pliers" but didn't know how to use it. Next time I'll try and if I fail, I'll just replace it with a regular screw style collar from an auto parts store.

For reference...Clic / Clic-R Collar Pliers - CV Boot Clamp - Mercedes Benz, BMW - - Amazon.com

3- I totally appreciate you documenting your "ignition coil puller". I did the same for coil #6 with a string wrapped around a screw driver...however mine was held on so tight I ended up popping the ignition coil right off the spark plug connector! I initially freaked out since I was afraid small parts may have been missing in between. Next time I'll make sure to pull from the ledge on the top side of the connector before the bend instead from the body of the ignition coil itself (assuming I can reach that low).

4- When reinserting the spark plug connector, I for the life of me couldn't figure out how to keep it on the spark plug. Only after watching/reading more online forums I found out you no longer hear a "click", but rather the spring just rests on the head of the spark plug. I simply just screwed the coils back hoping the connector kept contact with the spark plug head (which it did fortunately).

5- DEFINITELY use the grease. Just to test my spring theory above I put a spark plug into the spark plug connector while it was removed (without using grease) and it acted like a chinese finger trap! Again I freaked out, but now completely understand why the grease is required. Similar to your tutorial I used this...

http://www.amazon.com/Permatex-22058...ilpage_o05_s00


Knowing what I know now, I'll personally be doing the spark plug changes on all my cars moving forward.
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#10 Old 05-26-2016
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Quote:
Originally Posted by Justinqueensny View Post
First off a big thank you for your write up and detailed info.

I'm having one hell of a time with the wiring sockets on the coil packs. Not sure if anyone else has had similar experience but it feels as if they're going to snap with too much force.

I've changed plugs on older MB's and it's never given this much fight.
You just need practice. For me I ended up snapping the locking tab completely off on my first try.
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#11 Old 05-27-2016
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Quote:
Originally Posted by edgalang View Post
Odd that I didn't get a notification to reply to this thread until now, but since I'm here, I'd like to THANK YOU once again. Your tutorial gave me enough confidence to change spark plugs for the first time on any car!

Here's a few notes of my experience for those who might be in the same situation...

1- I ended up ordering from Amazon since I have Prime and had credits. This is what I used...BMW Magnetic Thin Wall Spark Plug Socket 3/8" Drive 14mm 12 Points - - Amazon.com
...and paired it with this...Amazon.com: TEKTON 4964 Impact Universal Joint Set, Cr-V, 3-Piece: Home Improvement

2- I really really wanted to remove the clamp @ step #8 . By keeping it on and just moving the box, I kinda thrashed the soft heatshield that is attached to the back of the airbox since it kept sliding down. I even had a "Clic / Clic-R Collar Pliers" but didn't know how to use it. Next time I'll try and if I fail, I'll just replace it with a regular screw style collar from an auto parts store.

For reference...Clic / Clic-R Collar Pliers - CV Boot Clamp - Mercedes Benz, BMW - - Amazon.com

3- I totally appreciate you documenting your "ignition coil puller". I did the same for coil #6 with a string wrapped around a screw driver...however mine was held on so tight I ended up popping the ignition coil right off the spark plug connector! I initially freaked out since I was afraid small parts may have been missing in between. Next time I'll make sure to pull from the ledge on the top side of the connector before the bend instead from the body of the ignition coil itself (assuming I can reach that low).

4- When reinserting the spark plug connector, I for the life of me couldn't figure out how to keep it on the spark plug. Only after watching/reading more online forums I found out you no longer hear a "click", but rather the spring just rests on the head of the spark plug. I simply just screwed the coils back hoping the connector kept contact with the spark plug head (which it did fortunately).

5- DEFINITELY use the grease. Just to test my spring theory above I put a spark plug into the spark plug connector while it was removed (without using grease) and it acted like a chinese finger trap! Again I freaked out, but now completely understand why the grease is required. Similar to your tutorial I used this...

Amazon.com: Permatex 22058 Dielectric Tune-Up Grease, 3 oz. Tube: Automotive


Knowing what I know now, I'll personally be doing the spark plug changes on all my cars moving forward.
You may not want to use a "screw style" clamp on any plastic hoses/tubing.
Apparently that type of clamp applies uneven pressure on the hose under the screw part of the clamp and over time can cause the hose the deform or even break.
I've used them myself in the past but don't any longer.

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#12 Old 05-27-2016
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Quote:
Originally Posted by edgalang View Post
You just need practice. For me I ended up
snapping the locking tab completely off on my first try.
To replace a broken locking tab, just purchase a new ignition wiring socket, A0275455026 (RECEPTACLE HOUSING). They are only $3 or so each.
The locking tab can easily be removed from the new socket and used to replace a broken tab.

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I would also like to add my thanks to WhiteRabbit for a great write up. I've been wrenching on cars for many years, but it's always nice to have some guidance on where to start and what pitfalls to watch out for.

A couple of notes from my experience that I would like to share:

1. I also had a heck of a time with the wiring sockets on the coils. About the third time a gray locking tab shot out of the engine compartment or broke off, I decided to leave the connectors in place. The wires have plenty of slack to keep the coils from interfering with removal and installation of the spark plugs. This made my life much easier and saved me a lot of time.

2. The OEM plugs have a "fat" insulator that allows the boot to seat properly. As edgalang mentioned, there is no "snap" to grab the tip of the plug inside the boot, the rubber acts like a "Chinese finger trap." (Great analogy!) The problem I had was with the aftermarket plugs (both Denso and Champion). They have a slightly thinner insulator. This causes problems with the grip and, together with the dielectric grease, does not allow for sufficient friction to make good contact with the conductor. I noticed the difference when I first saw the new plugs, but it didn't dawn on me that would be an issue until I installed them and could not get rid of the misfires. I'm glad I decided to try out the "easy" side first. For the record, the OEMs measure .040 inch and the aftermarkets .035 inch.

3. With regard to swinging the air box up and away. I found it helped to grab the rubber hose on the intake side of the clamp until the air box was perpendicular to its original location. This kept the accordion hose from kinking until the grip "broke" and the air box tube started to turn.

4. What's up with that back torx screw on the air filter housing? Next time I will replace it with a hex head screw that can be easily removed with an offset wrench.

I hope these observations make sense and will help the next DIYer that takes on the job of replacing their plugs.

Enjoy your Mercedes!
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#14 Old 07-09-2016
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Quote:
Originally Posted by W212 View Post
I would also like to add my thanks to WhiteRabbit for a great write up. I've been wrenching on cars for many years, but it's always nice to have some guidance on where to start and what pitfalls to watch out for.

A couple of notes from my experience that I would like to share:

1. I also had a heck of a time with the wiring sockets on the coils. About the third time a gray locking tab shot out of the engine compartment or broke off, I decided to leave the connectors in place. The wires have plenty of slack to keep the coils from interfering with removal and installation of the spark plugs. This made my life much easier and saved me a lot of time.

2. The OEM plugs have a "fat" insulator that allows the boot to seat properly. As edgalang mentioned, there is no "snap" to grab the tip of the plug inside the boot, the rubber acts like a "Chinese finger trap." (Great analogy!) The problem I had was with the aftermarket plugs (both Denso and Champion). They have a slightly thinner insulator. This causes problems with the grip and, together with the dielectric grease, does not allow for sufficient friction to make good contact with the conductor. I noticed the difference when I first saw the new plugs, but it didn't dawn on me that would be an issue until I installed them and could not get rid of the misfires. I'm glad I decided to try out the "easy" side first. For the record, the OEMs measure .040 inch and the aftermarkets .035 inch.

3. With regard to swinging the air box up and away. I found it helped to grab the rubber hose on the intake side of the clamp until the air box was perpendicular to its original location. This kept the accordion hose from kinking until the grip "broke" and the air box tube started to turn.

4. What's up with that back torx screw on the air filter housing? Next time I will replace it with a hex head screw that can be easily removed with an offset wrench.

I hope these observations make sense and will help the next DIYer that takes on the job of replacing their plugs.

Enjoy your Mercedes!
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#15 Old 03-24-2017
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Originally Posted by edgalang View Post
You just need practice. For me I ended up snapping the locking tab completely off on my first try.
Hi! Did you end up replacing the spark plugs on your M276 C350 successfully? Looks like the repair shops charge for min 3.5 hrs labor for replacing the spark plugs on a M276 C350 and this is motivating me to do it myself.
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Hi! Did you end up replacing the spark plugs on your M276 C350 successfully? Looks like the repair shops charge for min 3.5 hrs labor for replacing the spark plugs on a M276 C350 and this is motivating me to do it myself.
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#17 Old 08-24-2017
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4. What's up with that back torx screw on the air filter housing? Next time I will replace it with a hex head screw that can be easily removed with an offset wrench.
I have the 276 engine in my 2013 C350. First time I looked at changing the air filter I asked myself how is that back torx screw supposed to come out? Then I looked closer. You don't take the cover off the air filter housing before removing the housing from the engine. Remove the bolts that secure the housing to the engine first, then swing the housing up from the clips holding it at the bottom, then remove the torx screws and cover, then remove the air filter. The duct will flex enough to swing the housing up and remove the cover without having to remove any duct clamps.

Now I'm off to review the details on how to replace the spark plugs before they need to be replaced next year. Are they really indexed? Well at least it doesn't have 12 plugs like my old C320 that were easy to replace.
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#18 Old 08-15-2018
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Thank You for this How To, I am changing plugs in a couple of months and this information is great to have


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#19 Old 08-18-2018
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Well I replaced the C350 plugs back in June and it wasn't too awful. I bought the indexed plugs. There is certainly no reason to remove the intake manifold as one set of instructions suggested. No need to disconnect the air cleaner housing from the duct either, it will swing out of the way with plenty of room to get to the coils. Removing/replacing the engine controller is not difficult. The driver's side is harder to do then the other due to tight space by the plugs. Definitely use the dielectric grease to make the next replacement go smoothly. I agree it's hard to tell when the plug wire seats on the plug as it's a bit like pushing a wet noodle with the coil housing. Everything got put back together and worked fine on the first try.
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#20 Old 04-08-2019
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Question M276 (2012 up) spark plugs removal diy

Great PDF for changing plugs on the harder M276 engine.

Looking for additional information for changing the air filter, dust filter and any other "while you are doing the other thing, you should consider doing this at the same time!" type help.

Thanks,

Eric
Minneapolis, MN
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