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Not a mechanic but am mechanically inclined. I own a 2016 S550 coupe with a little over 50k miles on it. Was getting a misfire so decided to change plugs and coils. The #4 and #8 are a nightmare to get to on this car. Anyway finally got it and misfire went away but code didn’t. My bigger concern is what my #4 plug looked like. It has oils and black soot on it. I have a cheap scanner and it’s showing 4 stored codes (pic and video attached). Hoping to get a sense before taking to dealer
18 AMG GTC and 22 F150 Limited. Past owner 16 Maybach, 17 Brabus Smartcar, 06 Ford E150, and 22 G70
MIght be a good idea to switch coils from 4 and 8 to two say 1 and 2 and see if the problem follows. Also you hopefully used dielectric grease on the spark plug boots for the coils and also inspected them for any wear or pinholes where sparks can escape to the engine block. Actually coil boots are pretty cheap and worth considering replacing when doing a plug job.
Back to the codes also make sure that that fuel pressure code does not come back.
Yes I changed the coil too when I did the plugs. Codes stayed. My question was more about the condition of the plug and whether that was indicative of something bigger
18 AMG GTC and 22 F150 Limited. Past owner 16 Maybach, 17 Brabus Smartcar, 06 Ford E150, and 22 G70
Prolly ignore it and see if codes return. Could have been due to the previous codes. If you’re still concerned you could borescope that cylinder and see if there is damage.
Yes I changed the coil too when I did the plugs. Codes stayed. My question was more about the condition of the plug and whether that was indicative of something bigger
you might be confusing stored codes versus active codes.
Do you have any codes that say active next to them? If not, your scanner may be able to show you pending codes which are things to look out for but not consistent enough to set an active code.
Those are stored, they are there until cleared.
On the plug tip or outside on the ceramic?
If on plug tip you have a serious problem, if outside you need to change oil separators and head "cover" gasket.
Those are stored, they are there until cleared.
On the plug tip or outside on the ceramic?
If on plug tip you have a serious problem, if outside you need to change oil separators and head "cover" gasket.
Genericall yes, but not the type of problematic OVS that's in the M17X engines. The M278 engine has a more straightforward/conventional pcv valve design. I haven't heard any stories about M278 engine pcv valve failures. Have you?
Last edited by carlosinseattle; Mar 17, 2026 at 04:26 PM.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
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