Katie22

Hi all I have one of those lessons learned things. During covid i replaced the spark plugs for the GTC. Due to shortages (as best as I recall) I cross referenced Bosch plugs and used those. All seemed fine but in a subtle way I should have noticed that the trans was shifting differently in sport plus and race mode. One day months after the plug change I floored the gas pedal and the check engine light came on and reduced power was there as well. When I got home I used the scan tool to reset the computer because it seemed like it was a fluke due showing a misfire issue.

A few months later under full throttle same problem light came on and I further ran the scan tool and saw I had misfires all over the map in many cylinders. I decided to put the original spark plugs back in the car and still had a misfire problems but only in two cylinders.

The other day I decided to replace ALL the plugs with OEM spark plugs (well oem is NGK and NGK makes a same part number plug as whats on the original plugs so i got these at Napa) and replace ALL THE COIL rubber boots (oem as well). I used the special lube on the top of the boot where it pushed onto the coils and at the bottom where the plugs go. I moved the coils that were showing misfires to the other side of the engine (in case there was a bad coil it would show up on the scanner).

I can promise you that the second and third time you change plugs it goes much quicker!

So the new OEM plugs and new spark plugs boots solved the problem. Trans shifts correctly and engine runs strong!!!

THE END

PS the NGK non Mercedes plugs are SILZKFR8f7s which is the exact same number on which is on the base of the Mercedes OEM plugs. Also on the box for the plug is a stock number 97566

LAsunset

Still dreading swapping plugs on mine. Argh.

Btw out of curiosity, what were the exact CEL codes you were getting?

Katie22

Ok so after replacing the Bosch plugs with the original ones the codes I was getting was p030885 cyl 8 misfire and a misfire for cylinder 6 but i dont seem to have that one recorded (lost the paper I wrote it onto. With the Bosch plugs I was getting misfires in all the cylinders if I recall.

If you do do the job send me or ACta a message at least for me you can get my number and if you have questions I can help.

Ok I am no videographer but I did do a couple videos on youtube showing the tools i used and the stuff you need to remove to get at the coils.

Tools
video showing the stuff to remove on car

AMG 17GT

Ty Katie

I was curious as to why you did not replace the coils while you were down in there.

Katie22

Well statistically coils are not a big failure item, secondly I have gotten so quick to get the coils out that I was willing to give the originals a try with new boots and correct plugs.

PS the coils are made by Delphi since its stamped on them. Delphi was also on the coils for the Maybach I had as well. Funny to think a part is made in America sent over seas and put on the car and then the car shipped back here to America.

GTConn

As DIY'ers, we really appreciate your posts!

LAsunset

Katie, appreciate the videos! Thanks again.

Edit: qq. When you disconnect the ECU, would you recommend disconnecting the battery -ve terminal first? ty

Katie22

I am sure it says to disconnect the battery. I for whatever reason did not. My own choice I guess.

AndrewFerg

Hey Katie. Thanks for the update. You're comment about the coils is interesting because when I was getting the same error messages always at the high end of the RPM scale and under full acceleration, every tech I spoke to believed it was a coil problem and that we should replace the spark plugs while we're in there. No one thought it would be the spark plug. I just replaced both in the problem went away so I don't know which was the actual source of the misfires.

Katie22

Well bare in mind that after further thought I did not know when i first changed the plugs that the rubber boots were a part that you could buy separate from the coil. As I have said before removing the coils takes a lot of pulling effort and I could have undetectably damaged an original boot. Also understand that a repair shop does not have the time to simply replace the boots and see if that solves the problem. They can only do the job once and so thats a good reason why they recommend replacing coils which will come with new boots. This saves them come backs and lost profits. If I owned a shop I would probably say the same thing.

Also when i first changed the spark plugs I did not know it was a good idea to replace the boots. Come to think of it WIS does not even suggest this. Perhaps the techs dont realize you can buy the boots separate. I should also say that after 50000 miles the old boots were definitely harder than the new boots which could have contributed to misfires (not making a good electrical seal).

I guess in a nutshell my advice from this post is to use OEM plugs or the NGK equivalent (they make OEM) and while your changing them be sure to change the boots as well since they are not expensive. Be sure to use the special lube on the boots and plugs and care NOT to get the stuff on the contacts of the plugs and boots where electricity flows. Finally to clean with a wire brush or sandpaper the bottom bolt hole (where it contacts engine) on each coil since that is the path to ground that the coil uses.

cdk4219

Those look like the VW coils that are really hard to get off. I pulled the top of the boot off and then put an air blow gun onto the boot and pressurized it. It comes right off then. Pulling them is futile.

luvair

Katie22,

What brand and model scan tool did you use?

Very informative thread. Thank you.

Katie22

Oh like many of us I have the Icarsorf scanner. It by no means is what a dealer would be using BUT it does provide a decent amount of information and whats really cool is I can use it for other car brands (to a lesser extent) as well under the obd2 setting. LInk to the scanner is below on Amazon.