I know a lot of people are using techs to change their plugs and that may not be a bad idea on these engines.

Two warnings up front, the new plugs or any plugs installed must be Torqued to Mercedes spec to make sure the plug is indexed or MB says cylinder wall damage can occur. Second, removing the plug wires from the plugs is really hard no matter how strong you are Damaging the plug wires is easy during removal, so be prepared to replace a couple. The two plugs in the back of the engine next to the firewall are really tough and those are most likely to be damaged.

1) Remove air boxes and engine covers
2) remove large rubber coil fuel rail insulation and be careful to not break or drop the two plastic clips attached to them. Pic below shows large rubber coil insulator covers.




3) Remove all coil plugs and and go slow , so you do not crack the coil plug clips or locking tabs on the coil. Pic below shows coils with covers removed



Pic below shows short plug wires with hard plastic sheating on them. They have to be pulled straight out of the plug hole and room is very limited.



4) Remove two screws per each coil pack. Do not remove plug wire on the coil side but grip coil and plug and pull off the wire from plug side. Twist wire first and then pull. On plugs that lack room , you may have to use a open end wrench to pry wires or worst case, rip them off and replace with new wires Note: On Passenger side, it helps to remove the one screw and clip that holds a wiring harness over the spark plug area.

5) Remove old plus using 14mm socket.

6) Note: Stock plugs are gaped to about 32 thou and if you are adding mods or tuning your engine, then colder plugs are needed. Also a tighter gap helps under heavy boost.

7) Put a drop of engine oil on each plug thread before installing and then drop the plug in the hole. The plugs on this engine are pretty much self guided into the threads, so pretty easy to get them started.

8) follow reverse order and re-install all parts.

Tools needed are 1/4 drive ratchet, swivel and several size extensions.
Flat head screw driver, 2 x 3/8 drive 3" extensions and swivel, plus 3/8 ratchet and 14mm deep socket.
3/8" torque wrench
Spark plug gap tool
Di electric grease to put back on the plug wires , so next time they come off easier.
E8 torx socket

MB master tech told me 23NM torque setting for the plugs but double check the torque spec before torquing each plug.

 

Nice Brooke. Vote for sticky...

 

Just a bit of info. Replaced my spark plugs on my E550 Coupe (M278). It didnt use the standard 14MM socket. It used the 12 point 14MM Socket.

 

Thanks for the basics.

So the only thing special to "index" the plugs is to ensure the proper torque, correct? There are no special marks to line up or anything? (assuming I will replace with the OEM plugs)

Does anti-seize on the plug threads affect the torque application? Is this why you use a drop of engine oil? I always wondered this for any torque application where anti-sieze is used.


Off-subject question: are those air filters the "special" $400 ones with basically just a plastic spacer between the halves of the airbox? I saw them somewhere and thought it would be easy to replicate the spacer and achieve the same effect, like using a 3D printer.

 

Oh, and what is the proper torque on the plugs?

 

A little bit of searching online shows that anti-sieze definitely lubricates the threads and affects the application of torque. This can also be true with loc-tite compounds.

Considering the sensitivity of indexing the plugs, I suppose this will be the first time that I ever put in new plugs without it.

I found a document from Weistec with step-by-step install of their plugs for M278, and it says nothing about putting anything on the plug threads. It seems the threads should be dry for proper torque application which results in proper indexing.

http://weistec.com/media/productfile.../m157spark.pdf

 

How often do these engines need plugs replaced or was this done to change the type of plug for higher boost levels?

 

Check the maintenance schedule for your vehicle year and engine. The M278 V8 shows every 60K miles schedule.

 

Based on what some engineers have told me, there should never be any lubricant on the threads to which you are trying to torque to spec. Doing so will result in over-torque. The threads should be clean and dry.

 

every 60K miles stock per MB...

for tuned, most tuners recommend every 10-15K miles

 

This is what NGK says, too.
https://www.ngksparkplugs.com/about-...-spark-plugs#!

"NGK tech support has received a number of tech calls from installers who have over-tightened spark plugs because of the use of anti-seize. Anti-seize compound can act as a lubricant altering torque values up to 20 percent, increasing the risk of spark plug thread breakage."

I'd say if you were set on using anti-seize or some other lubricant, adjust the torque value accordingly.

 

Bumping an old thread because what i read there is still two groups as far as which plugs to use.

Group 1: OEM only.
which apparently is part number 004-159-81-03. Correct?
From my dealer = $38 each
Online = $15 each

Group 2: A plug is a plug, the dealer doesn't install any magic sause.
NGK part number ??
Bosch - ZR6SII3320 = $9 each
and many other vendors.

Since i am not too rich i'll skip the dealer option, but just want to verify the 81-03 part number is what folks are using. My dealer was less than helpful.

thanks guys.

 

oem is bosch ZR6SII3320 (0041598103)

https://www.boschautoparts.com/en/au...tId=ZR6SII3320

 

Thanks for a great DIY. It inspired me to do it myself. I like to add the following for others to do it themselves.
Some more tool tips to make the job even easier.


E8 torx universal swivel 1/4" drive socket for Removing the ignition coils - 1/4" drive x 2" extension. This is almost a must to remove coil #4.
Removing/installing spark plugs - with a cold engine,
GST Flexible spark plug socket 14mm (Amazon), 3" extension, and ratchet. Again, very limited room to access #4 & #8. GSTsocket is 3.5" long. Too short and you won't have room to maneuver torque wrench. Too long and you won't have room to attach torque wrench. Make sure you wrap a wire around the swivel to pull it off the spark plug after it is tightened to 23NM with a Norbar 60 torque wrench.i suggest having 1 spare ignition connector just in case.

Removing the ignition connectors - with a warm engine, use a Pittsburgh hose pliers (Harbor Freight) to grab below the coil and pull very slowly up without twisting. Not a lot of tools but all were much needed. Substitute the torque wrench if too expensive but make sure it can do 23NM.
Also, torque all of the plugs before reinstalling the coil connnectors because you need the room.
​​​​​Take your time and enjoy.
​​​

 

Just did this on my SL550 yesterday - the above tools are the ones you need.

I am not sure why any of you are using wrenches to pull the connectors; there isn't enough room for anything - I even bought a fancy set of BERU pliers from Baum tools that ended up being totally worthless; here is what you need:



You take this and do a crimp loop and then a loop-to-loop connection over the connector; make sure you slide the loop UNDER the plastic tab so you don't damage the coil pack connection:



Here's the first one removed:





Here is what you need for proper indexing; the correct torque per Weistec is 20 N-m which is around 14.75 ft-lbs on the standard torque wrench; torqueing to that puts the ground strap directly under the plug and faces the electrode right at the piezo injector; I taped a piece of paper with red line to the socket extensions just in case:



Job went perfectly smooth and easy without destroying any connectors - don't waste time with stupid wrenches in such a tight space, and be sure to put dielectric grease on the ends of the connectors before re-inserting them.

Now my computer is off to Weistec for reprogramming.

 

For those looking to tackle the job I offer the correct Bosch plugs and the thin walled spark plug socket tool at this link

--Kyle

 

Part number update? If eBay is to be believed, the OEM part number for the Bosch ZR6SII3320 plugs is now 0242140521, not 0041598103. Can anyone confirm that the older number has been superceded?

 

God, it's a fiddly job! Well, it is if you have big hands...

So far as altering plug gaps goes, Bosch specifically advise against trying to do this on Fine Wire plugs, which these are, so as I have a stock engine, I left well alone.

To remove the coils and leads from the plugs, you can either just pull the damn things off as a unit, trying to grip the coil end of the plug lead while doing so, and risk damaging the conducting core of the lead, or if you're a fisherman, see post #15 above, but I found that using quite long cable ties (you call them zip ties, I think), pulled tight on the plastic sheath, below the tab which is there to help you get the lead fully home on the new plug, worked very well - it was quite easy to apply enough force to pull the lead off the plug.

 

 

Bosch ZR6SII3320. They were a bit cheaper than a set of OE MB ones, and when I removed the OE MB plugs, they were in fact Bosch ZR6SII3320 anyway, but with an MB logo on them. £2 a plug for an MB logo seems a bit pricey...

 

 

Indeed I did. (I first tried hooking a bent screwdriver under the tab and pulling on it, but that didn't work; it broke off... looking at its design, the tab is there to help you push the wire lead fully home on the new plug, not pull the wire off). I used 14-and-a-half inch long ties, so there's plenty to get a grip of once it's in position. It was quite easy to get the loop down past the tab and pull it tight, and once that was done, getting the wires off was fine.

The two rearmost plugs and wires have very little space to pull outwards in, and I had to use a screwdriver held horizontally along the side of the cylinder head to pull the tie around, through 90 degrees, so I could pull it straight up, but that did the trick.

It's a very basic job, but because of how little space there is to work in, it's quite awkward and time-consuming, and be warned - there are plenty of sharp little projections to take a bit of skin off...

 

 

Thanks to member @konigstiger the attached are the official Mercedes instructions. They use a special puller tool for the plug wires. I wonder if it can be purchased and how much?

Note the torque specs in this guide are 23 Nm for the plugs.

 

The puller part number is in the instructions you attached. Looks like its around 50 bux, may have to try it next time I do spark plugs. Also the new part number ignition coils are much more sturdy then the old ones, something to keep in mind. When I removed the coils on my 2012 cls63 I used a long mini usb cable wrapped underneath the plastic extrusion on the coil and removed all of them without any damage.