There are different opinion about the need for indexing the plugs for the DI engines and this discussion could have its own thread, but if we for the sake of it stick to the MB recommendation that plugs need to be indexed correctly DO NOT buy the FCP plugs that are mentioned to fit. Yes, they do fit but do not index correctly.

They also sell Genuine Mercedes plugs and these probably do index correctly but cost 3-times more.

I changed plugs in my 2012 S550 and bought the kit from FPC but the plugs did not index correctly. Had to sand every plug washer down to 1.25-1.30mm thickness from the 1.50mm that they came as.

While doing this project I read that NGK plugs do index correctly and those are what I will buy next.

It is just amazing what all "tricks" MB does to maximize their business. The spark plugs between the MB-logo Genuine Mercedes BOSCH plugs and the regular BOSCH plugs said to fit (available everywhere) are exactly the same other than the end point of the plug thread. In MB Genuine plugs the thread ends 90 degrees later that sets the plug electrode direction correctly. The regular plugs stop 90 degrees short when using the correct torque.

FCP calls both plugs to fit, which is not correct if the indexing really matters.

NGK makes plugs to fit and index correctly and this same plug will work also in the older engines that are not DI. MB could do the same, but they probably prohibit BOSCH from making the correctly indexing plugs for general distribution for the lower sales price.

Also, if you look at the spark plug numbers stamped in the plugs, the Genuine MB plugs number starts "Z 6S113..." while the general plug number starts "Z R6S113..." so the plugs are not the same. But yes, they will both screw in the hole just the same and fit...

 

I thought couple years ago, Surya studied the genuine MB plugs to evidence they were not so well indexed either pointing at factory for engine heads machining.

> Indexing... save time:
-- 100kMi lean misfires are not caused by nearly indexed plugs but more likely unbalanced cylinders.

-- The ECU is unable to compute random timings, mixtures are misfired then sanctioned by lean fuel thats even harder to ignite.

 

My flex-fuel car came with genuine OEM plugs made by NGK, they were not the part numbers you suggest, they indexed correctly, when I change the plugs in my gas car, I will again use Genuine plugs likely made by Bosch with those part numbers and would expect they will index as well, When I say Genuine, I mean MB plugs

 

Indexed or not indexed, that is the question. Wow, yet another wrinkle, courtesy of MB Best or Nothing blahblah!

For our 2014 E350 gas (not flex fuel), FCP doesn't list the NGK and has only the Bosch at around 73 bux, and the MB at around 234 bux ...that's a freaking no brainer to me! Someone please tell me this MB indexed plug thing is like an Apple-mafia move and I'll be fine with the Bosch. Man, gone are the days when regular maintenance was actually affordable, not to mention readily doable without having to do a triple backflip with a half twist! This is a 2014 fer crying out loud ...not even close to the newest of the new gizmos, sheesh!!!

Edward

 

I have the same setup: MY'14 - 3.5L ...
buy the FCP Bosch kit including thin socket

QA the GND electrodes for obvious burrseasure opening gap where you want it

Have some fun:
You will be pleased when comparing all the plug thread indexing being all equals. Double check minor indexing discrepancies are from MB engine heads.

Replace new boots.
Don't use anti-size compound.

 

My part numbers were for BOSCH plugs and after what I learned I will not buy any BOSCH plugs for anything anymore. It will be NGK that I used for my 2010 S550 90 000 miles ago. Only changed plugs once at 100 000 miles to NGK and it is still running like silk.

 

Even FORD GDI engine uses indexed spark plugs

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Me simply buy genuine MB spark plugs from authorized dealer. Safest bet in a world full of fake craps.
I will replace spark plug every 5 years or so, so far I have replaced twice on my own and I am only at 44,000KM max.
I worry more of the male steel thread of s-plugs getting seized to ALUMINUM block female thread, not about wear and tear on the s-plug tips.

On my friend's M271.820 4 cylinder engine this is how his plugs looks like at 70,000KM. The super small tip is gone already.
This is GDI engine too, but 120 BAR and not 200BAR like M276/M278/M157 family.

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Used, +-70,000KM




The 4 new ones are 3 are 0.75mm and 1 is 0.80mm


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I bought him genuine MB only, nothing else. It is too low cost to risk.


+++ ADD

Member Tesna engine M272, when using genuine Bosch but not MB version, his fuel trim can not be as good as MB s-plugs.
The plugs built-in resistance is also a bit different.
So he tried MB genuine and all good, suprise suprise and this is not about fake Bosch, it is about MB custom spec ordered to Bosch.

Hope Tesna chimes in........

 

Correct, although FCP does have the flex-fuel equivalent to the NGK in Bosch

 

I have a real hard time finding the MB/Bosch cross referenced into NGK for non flex-fuel.

I would luv to try an upgrade to high-ignitable NGK if the classic connector tip was available instead of the flat-top option.


I can say my original plug set came out as good as new at 50kMi. It would have easily gone an extra 25kMi and likely 100kMi without any issue despite all stock setup then.

Still... no way I'm buying MB stamped Bosch plugs. Besides I have a free replacement set waiting for me at FCP.

 

I didn't see that either, just the Bosch supposed equivalent of the NGK for flex-fuel cars, I am relaying my experience with my flex-fuel car replacing the plugs at 60k miles, I used the MB genuine NGK's and they indexed correctly.

 

SURPRISE!!!

Actually, it’s not impossible for DIY and you will know for certain that it is done right. I highly recommend watching some YouTube videos on how to do it first, but don’t try to take shortcuts. Removing the intake manifold will allow you to complete the job properly. I’ve done it several times and always remove the manifold, but that is just me.

 

+1 : all shortcuts R not helpful.

There are many excellent reasons to pop the intake for this job.

Disable the stock $10k oil nightmare is No1.