If you haven't done this on your own yet ... let me tell you it's a huge pain in the a$$.
I didn't take any pictures, but will share a couple thoughts for those who may want to tackle it on your own ...

Took me about 4.5 hours. It was honestly harder than changing all 16 plugs from my E55 AMG ... but I did those while changing my valve cover gaskets, so I had extra room ;-)

2014 GL 550 with 65,500 miles.

I have the MB Shop Manual an it helped in most cases ... but there were a few items it was missing.

Batteries -
Make sure to unhook both batteries since you'll be messing with the ignition system (coils).
Primary is under the passenger seat (move seat all the way forward and remove the panel and disconnect the cable.
Secondary battery on mine was located in the back accessed via the spare tire compartment, pulling back the compartment "interior" from the right hand side to access the battery in the body compartment.

Pulling off the air filter housing -
Make sure you get all the electrical connections disconnected.
The drivers side housing has a hose connected to it. If that hose has never been disconnected from the housing in the past, it will have a factory pinch clamp on it. My advice is to remove the pinch clamp, and replace it with a regular hose clamp. Do NOT try to pull the hose stub from the air filter housing, you'll break the stub from the housing.

This is a great opportunity to change your engine air filters

Remove fuel rail insulation -
It looks like the insulation just sits there, but there are actually two little clips on the side of the insulation that clips it to the fuel rails. These things break VERY easy. I broke both of the clips on the drivers side before I figured out how it was connected. Take your time and gently pull up on the top and slide your hand down between the fuel rail and inside of the insulation and push the side away from the rails.

The ignition coil connectors are a bit tricky ... pull the gray "lock" back, then push down on the gray "lock" to disengage the clip and pull the connector off the coil (while holding down the "lock".

Remove the ignition coil bolts

The coils are very hard to remove off the plugs. I used a trampoline spring hook to help me.
There is a little plastic hard part on the outside of the boot (you'll be able to feel it with your fingers) that you can get the hook on and gently pull it out.

Heads up ... The spark plugs are recessed ... and you won't be able to easily pull the socket off them.
I used a cheap socket from Autozone (didn't have a 12 point 14 mm spark plug socket in my toolbox) and wound up using 50 lb spider wire (fishing line) to tie the socket to the universal I was using. This allowed me to use a pair of bent hemostats to painstakingly pull the socket off each plug :-(

Do yourself a HUGE favor, and get a 12 point, 14mm spark plug socket that has the swivel and extension permanently connected to it like this https://www.ecstuning.com/b-genuine-.../278589000900/


This will save you probably 45 - 60 minutes of frustration!

Other than that, it's pretty straight forward. Of course the back plugs and coils are a pain to get a torque wrench on, but it can be done.

Spark plugs are torqued to 23 NM
Coil bolts are torqued to 9 NM

Hope this helps.

Eric

 

Thanks for your post, I’m due for a spark plug service soon and it was a good insight of what I’m getting into

 

Eric, you are spot on with regards to it being a huge pain in the a$$.
Why did you change your plugs? Just routine or was it missing a bit? If missing, did the new plugs do the trick?
I have a 2013 GL450 with 65k miles and it is running like it needs new plugs.


Last night I changed brake pads and oil before moving on to swap in new plugs. Pffffft.
Took me 30 minutes just to get to the point where I realized I needed a 12point spark plug socket. That's how I found your post.
Those rubber boots are not easy to get off.

Looking forward to doing this.

 

Routine @ 60k miles. Hasn't missed a beat since I've had her.

 

Thank you for sharing your experiences and posting the pdf. I am an avid DIY-er but new to Mercedes, recently purchased a 2014 GL 550 in the spring. It is now at 62k mi and due for plugs. I would prefer to do this myself rather than the $518 dealer quote. A couple questions for you:

1. The spark plug replacement sheet shows two different plug wrenches. 278589000900 appears to be a 12-pt deep socket with universal and long extension, and 112589010900 appears to be a 6-pt with universal and short extension. Are both of these needed? I see you highly recommend the 278589000900 and will buy that for sure, but I'm wondering about the 112589010900.
2. How many spark plugs? I haven't even removed plastic covers to look. I've read some Mercedes take 2 plugs per cylinder, so wondering if this engine takes 8 or 16 plugs.
3. Which plugs? I would like to use OEM plugs and don't see a part number in the sheet you uploaded (odd...) just a part number for the grease.
4. Factory service manuals - where do you find these things for newer model Mercedes? I've been searching on Google for 30-minutes with no luck. Where/how did you obtain these PDF printouts? I'd like to buy a big OEM hard-copy manual if possible, otherwise I suppose a DVD version would suffice. I just can't find them. Is this dealer access only?

 

I only needed the 12-pt socket, not the 6-pt for the 550. The 350 diesel may use the 6-pt, but not sure about that.
Best I recall ... the GL only has one plug per cylinder. My E55 has two, so what you read is correct. All depends on the motor and model.
I don't recall the plug part numbers, but they were OEM. Picked them up from the stealer.
For the manual, I bought something like this (https://www.ebay.com/itm/MERCEDES-BE...YAAOSwe2FZyMpI ) from ebay.
It's a Virtual Machine that runs on your laptop and is already setup with both the electronic workshop manual and the electronic parts catalog.
It's really nice for me as it covers both my E55AMG as well as the GL550. You enter the VIN, and it gives you specific information for your specific vehicle. There is a fair learning curve to using it however, so you'll just have to play with it for a while to learn it (I've still not mastered it).

 

Thank you for this post. I bought a used GL550 2014 and thinking of doing this sooner than later. I'll try to take photo in the process. Cheers.

 

I'm looking to do this job myself, Does anyone know the material type of OEM spark plugs? Platinum, double Platinum or iridium?

 

This is a bit cheaper than ECS Tuning.

https://www.oediscountparts.com/part...t=278589000900

 

PLEASE, BE PREPARED BEFORE STARTING THIS JOB.

I have been thinking about changing my GL550's spark plugs, it is time. Thanks for the great info posted here.

I bought the original Bosch spark plugs on RockAuto for 5.34$

https://www.rockauto.com/en/moreinfo...305919&jsn=599

Also, I bought the 12 socket extension to easily remove and install the spark plugs, because space is really tight.

I did not have a female torx socket to remove the ignition coils' screws, so I had to buy one set on Amazon. I just want to do this change in one day without stupid delays.

https://smile.amazon.com/s?url=searc...ds=torx+female

Do not forget this about disconnecting the driver's side air filter: You have to buy a hose clamp before start doing this. I almost break it.

"The drivers side housing has a hose connected to it. If that hose has never been disconnected from the housing in the past, it will have a factory pinch clamp on it. My advice is to remove the pinch clamp, and replace it with a regular hose clamp. Do NOT try to pull the hose stub from the air filter housing, you'll break the stub from the housing."

Finding videos about this task was not easy. I found this about replacing spark plugs in an S550, the same engine as my GL550 as far as I know. Hope this help other members of this forum:


I will try to post pictures.

Good luck!

 

Thank you so much for your post! I was able to change the 8 spark plugs in my 2014 GL450 X166. It is super helpful!

I had a code P0307 Cylinder 7 misfire detected that popped up a few months back. After clearing CEL, it would come back in a few weeks. The engine would hesitate and start running rough, then the CEL will blink and stay on. After clearing the CEL, it would drive fine for a few weeks and come back.

I bought a new ignition coil for cylinder 7 and 8 new Bosch spark plugs. The ignition coils were difficult to pull off. I got some thick steel wire, made an oval loop with it, and used that to hook on to the ignition coil stub which allowed me to pull it up. The replacement spark plugs went in well. When reattaching the ignition coils, it went in very smooth. There does not seem to be any "click" to engage the ignition coil boot to the spark plugs. I tried inserting one of the old spark plug into the ignition coil boot and it simply bottoms out with no click. Based on this, I am unsure why the ignition coils were so hard to pull out... maybe there's a suction or the boot tightens around the spark plug upon heat.

Be careful and watch out for the coolant overflow tube. When I started the car to final check, the coolant was spilling out the front by the serpentine belt. Mine was brittle and it snapped. I had to order this replacement part 1665001091.

Overall experience for the spark plug replacement is not bad other than the super tight space for the back 2 spark plugs on each side. I would say to set aside at least the whole day with lots of patience!

Cheers!

 

why are these cars so hard on plugs are these copper from factory? Iridium’s and double platinum last over 100k

 

The original spark plugs are Bosch Iridium that came with my GL450 since new. I am now at 125k miles and got the CEL for cylinder 7 misfire. When I took out the spark plugs, they all look good! The center electrode and the ground electrode still looks good with no noticeable wear, but since I think the maintenance interval is 5yr/100k, I figure I'd change them out while replacing cylinder 7 ignition coil.

Love my 2014 GL450 and thinking about trading to the newer GLS450 hopefully when supplies and prices come down a bit.

 

Does anyone have the cylinder order for the 2014 GL 550 ? I need to change the #2 coil pack. Thanks

 

From my research, when you are standing in front of the engine:

From left front 1,2,3,4
From right front 5,6,7,8

Hope this helps!

 

If you're correct, then yes it helps - Thanks !

 

Hi. I realize it’s been a little bit and wondering if you ever found out why no “pop” when reconnecting the boots? I noticed as well and no answers..
thanks for your post
scot