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Discussion Starter #1
I had my spark plugs changed out at 100,000km.
bought NGK iridium oem from aftermarket , checked NGK website and the part was suppose to fit. Had my mechanic changed it out and he pointed out that Mercedes had put out a TSB on the use of non factory plugs causing potential engine damage. Apparently , the position of the spark plug head relative to the intake valve is important in GDI, something like a 42 degree angle.

the engine with the new NGK plugs seem to run fine initially after the swap out. But I always did notice there was some tinge of gasoline smell at start up. I thought nothing of it , and drove it for over a month and finally decided this smell was weird , and the gas consumption was not great. So I bought new Mercedes plugs and had it changed out again and asked my local German auto mechanic to OBD the engine. There were some faults picked up , something to do with the charge induction short circuit, associated with the turbo intake. But there were no CEL the whole time.
Now the engine seem to run really smooth and gas consumption seems to be back to normal.
I think these engines are built to really high spec and the tolerances are really tight.

man, I am glad to replace with the Mercedes specd plugs.
 
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Mav, What "gap" did he use?
 

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Not gap ... angular position of ground post
Loooooooong time ago on here we had an ignited plasma propagation discussion that involves the shadowing effect of that post relative to how the flame front will travel taking into account valve dynamics and the fluid dynamics that stems from that etc etc
Bottom line - when I yank my plugs out if those have a “Mercedes” spec that is a few degrees off from the ngk ones (despite their oem claim) you bet your sparking butts i am gonna get oem ones ... they probably do a presort of large oem batches as part of the q/a process which then drives up the “benz” part but hey its a one time part (and labor time) cost that will run 60k mi so its a no brainer
Gas smell may well be from incomplete burn and thus lowers efficiency degrades the oil faster screws up the sensors lowers mpg etc
 

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You have another option like NGK Iridium IX as an alternative too, and not use economy spark plugs like Bosch Super Copper.
 

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Discussion Starter #5
You have another option like NGK Iridium IX as an alternative too, and not use economy spark plugs like Bosch Super Copper.
The issue is not with the overall quality of the spark plug. The NGK iridium plug I purchased is a high quality plug, but the specs (position of the firing electrode relative to the intake valve position) is not quite in line with the specs laid out by Mercedes for it's GDI engine. Apparently, anything slightly out of the positioning specs (Mercedes) , will cause it to mess up the combustion flaming pattern and process, leading to potentially damaging pre-detonation. The gapping of the NGK plug I had used was fine, just that after torquing to the spec, the position of the electrode is not quite where it should be relative to the mercedes spec.
 

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Yup ... i can see slight variations in the new plugs already (thread start vs ground stem)
Though i have not seen the thread start variation in the head yet as original plugs are still in
So my plan was to play musical plugs and manually match the plug/port for most uniform mounted angular position of the stem and hope they match the originals
Buf if not and the new plugs dont match the old plugs but a lot then will toss the new ones and bug benz for a set
Plug change aint cheap in terms of time so just wanna do this once
 
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