Did any of the mechanics think to totally drain the tank?
I had a 2017 S63 and when it hit the 70,000 mile mark, I too had the problems you described twice in the same day. The first time it happened I was 50 miles away from where I live. Fortunately it happened for the second time only one mile away from my dealership so I limped it into the shop. They ran diagnostics and all they could find was that it had a misfire. I left from there and for the next 10,000 miles it never happened again. I know you guys will slam me for saying this but I had always put regular unleaded gas in it up the time of trouble (70K miles). I did fill the car up that morning when the event occurred and almost within 20 miles it stalled on me, got it to crank back up, drove back to my home area when it happened again, and I took it to the dealership. From that point on, I used supreme grade fuel and it never happened again.

Thanks for sharing man. I've always put 91 gas which i believe is Supreme in that case, nothing lower than that.

I'm inclined to think it's the gas, too. Especially, if @Hedges had similar issues with another car while using the same gas stations. This may also explain why the dealership doesn't catch the issue when the car was kept for an extended period...and also why it worked fine for a while when it was returned home. It still has the gas in it from the dealership.

Regarding the Porsche Cayenne Coupe that you are considering as a family ride for 3 kids (and I assume a spouse). They aren't that big inside and the boot is small. They all have the cockpit of midsized cars. All Cayennes and Touaregs have been like that from the beginning. The Q8 is larger, though. It's basically a long wheelbase Cayenne/Touareg. The Panamera can feel kinda tight at times. It's on the snug/sporty side.

I think only the Panamera wagon has seating in the center of the rear bench...so only spouse and 2 kids can ride.

The Audi S8 was on my short list for sporty family rides. It ticks almost all of the same boxes as the S63.

About gas, even if it's 91 octane...it could be sh*tty 91 octane. There have been reports of gas stations selling gas that has water in it, either due some issue with the underground reservoir (condensation or rainwater) or shenanigans.

Texas:
https://www.nbcdfw.com/news/nbc-5-re...storms/266308/

Indiana:
https://abc57.com/news/local-gas-sta...-in-fuel-pumps

Boston:
https://www.boston25news.com/news/25...ars/925444449/

I was contemplating why all the issues were happening on s63, cls63 and recently my dad's S560 as well. The only thing i can think of was using Petro Canada 91 gas that all our cars have used. I got my car back a month and a half back ago , I started to only use Shell 91 for my car now knock on wood nothing has happened. I am starting to believe it could be the gas well and more specific certain brand gas stations. Prevoiusly it would be almost exactly 1 month before the car started showing the same symptons but so far it's been over a month and all is fine.

In regards to the Porscye Cayenne Turbo , I am going to give it a try for few years. Dont intend on keeping it but to only just try something new for fun. I originally wanted to try to get a Gwagon to play or a Porsche Panamera however both have no allocations or have to wait too long or out of my price range on the second hand. My warranty is up for the s63 as of this month , so this is one reason i'm switching out given the many problems i've had so far. Wife has a gls450 so we can use that as a the family hauler if needed lol

You could try a different petrocan if you want to stick with petrocan (but I personally prefer shell 91 with zero ethanol, just me though), believe it or not despite the same gas station brand the refineries could be different in different locations.

Now I'm even more inclined to say it's the gas.

The S63, CLS63 and S560 (essentially an AMG S63 Long Comfort) all have engines that are tuned to get the most out of the gas. I would venture to guess that these cars require at least 91 octane whereas other MB engines (like that in your wife's GLS450) can even run on "regular" 87 octane gas. Maybe her 3.0L turbo inline six engine can tolerate the bad gas. Even if they recommend "premium" MB (and other manufacturers) have to make their cars somewhat tolerant of bad gas if they want to sell their cars around the world. The AMG team probably expects really great gas for their engines, and tune the ECUs accordingly.

I've done ECU tuning on several of my cars and there is often a 92 or 93 Octane tune available that unlocks a few more HP...but if you select that 93 Octane ECU tune and don't give it at least 92 Octane, the engine starts to act up.

Here is an example of the tune in use:


And before any of you say, "My car isn't a Subaru!!". Your turbo AMG has a lot in common with a turbo Subaru when it comes to releasing horsepower. Basically, when you can't add more displacement, add boost via a supercharger (as in my W211 E55 AMG) or turbo charger(s).

All ECU tuning for AMG, M, S/RS, cars center around manipulating boost pressure.

Anywho...to bring it back home, you need clean high octane gas to get these cars to perform how you expect an AMG turbo V8 to perform.

For sure, previously we use up to 4-5 different Petro Canada stations whichever that is close by and we take advantage of the points card. However i've stopped using them and trying only Shell 91 now since i've goten back the car, it's been month and a half and so far no problems. Perhaps we can put this to rest with these stupid problems. Guess not all gas companies are the same despite fueling based on "91"

Ya stick with shell, petrocan has ethanol as well so....
Here are other gas stations without ethanol: https://www.pure-gas.org/

Wow on that list not even Petro Canada is listed in there

Ya, I used to use petrocan back in the days too because of petropoints but then CIBC decides to stop collaborating with petrocan so I tried something new (in this case shell 91) I realized how much happier my car feels after switching to shell 91 it accelerates smoother and it wasn't in my head (I tried many petrocan and shell within the GTA and all the time shell 91 feels like the engine runs smoother and the car pulls more) I am curious what refineries petrocan get their gas from but each petrocan indeed gets gas from different refineries.

It's been close to 2 months since I've gotten the car back and only filled with Shell 91. So far no problems! It's always within the 1month or 1.5month mark i'd start seeing the loss of power / knocking / shaking etc.

Good news to hear! Thank you for your update! Enjoy it : )