Merlz

Long time lurker, first time poster...

I didn't want to post in a similar topic thread from @Quenthel and hijack it, and I can certainly relate to your experiences, with CEL & the entire car shaking due to misfires, I'll be following your updates!

I have a 2020 S560 (V8) and also get misfires, but on cylinders 5, 6 & 8 for the past 2 years, the car only has 63k kilometers on it, and I bought it with 16k. I've had the coil packs, injectors and spark plugs replaced, compression & borescope tests done numerous times. Both Mercedes Romania & Germany have brought out technicians to investigate the issue, taken all the engine data for analysis and so far the underlying issue can't be identified. The car is in the shop today getting the fuel filter replaced, and additional tests since the misfire has been happening almost weekly during the summer, some days it occurs one after the other (have a misfire, pull over and "reboot" the car, start to drive away and the misfire happens again). If the fuel filter doesn't fix it, the ECU will be replaced next.

A few months ago the dealer was finally able to replicate the misfire, while driving the car and taking the engine to 5400 RPM, however the misfiring isn't related to only high engine RPM, I've encountered it while coasting in traffic, slowing down (braking). I did notice a few weeks ago, that while trying to accelerate, there was a ~3 second hesitation from the moment I put my foot on the gas pedal and to when the car started to accelerate, and then it misfired. I try to keep some mental notes to the engine RPM, fuel tank level, and any abnormal engine hesitation prior to a misfire happening. I started to see a trend where most of the misfires would happen when the tank was between 1/2 and 3/4 full, not every time mind you, but generally in that range and more frequent misfires during the summer months compared to winter.

I usually use 100 RON fuel (95 RON if 100 is not available), and it doesn't make a difference to stop misfires, misfires seem to happen with 95 or 100 RON.

I'm at the point where I'm discussing with Mercedes to buy the car back as it's no longer enjoyable to drive due to the thought always in the back of your head, will it misfire today, and it forces you to change your driving style. No longer do I stomp on the accelerator to pass a semi truck or slow moving vehicle on the highway, I look for a long gap now, just in case the misfire happens during passing (the deceleration due to a 3 cylinder misfire is like hitting a brick wall, and the car cannot maintain the current speed, or accelerate, you must slow down and pull in back behind the vehicle you were overtaking, while hoping that nobody is behind you, also trying to overtake a slow vehicle).

Does anyone else have any suggestions or experience with this, I love the car, but not the misfires and don't necessarily want to get rid of it, but don't know what else to do?

Quenthel

Hey Meriz,

Sad to hear you suffer from misfires, though in your case I think the problem might be worse than mine. In my case, it would misfire, hesitate for a bit and then I'd assume it turned that cylinder off because it would start shaking like jello, constantly. You seem to suffer from random misfires and on random cylinders.

I am far from a mechanic; couldn't change a spark plug without losing a screw or two, but if they cannot identify the issue easily, it can get time consuming and expensive based on what I was told about possible scenarios with mine:

1. They would first check the coils & spark plugs, because those were easy to remove. That's where we stopped,
2. Then they would have to disassemble the engine a bit more, to get to the injectors,
3. Then they would have to check the fuel filters,
4. Then do a compression test (IIRC),
5. Potentially needing a new cylinder head. That last part can get quite expensive in parts, not to mention labour.

Were I you, I would probably give it back, unless they can offer some warranty in case it happens again, just to be sure it won't cause worse damage down the line. Good luck with it and hope they will resolve it.

lucas zheng

Hi ,

I hope you can read my reply .

i have a 2018-2019 s560 cabriolet, 35k km so far , and already had 5,8 misfired , and cel is on again , waiting to check the code on next Monday .

just want to know how did you manage to fix your problem?

thanks

VII

Always same cylinders?
Also happens when low or no throttle?
I can see why they are thinking to replace DME, unlikely to be fuel delivery with those symptoms.

Merlz

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Hi Lucas,

I was not able to get the problem fixed, so just before the 2 year buyback protection was about to expire, I sold the car back to the dealership (for a $10k loss). It is very unfortunate, as it was a great car, but I lost all confidence in the car, specifically the ability to pass other cars on single lane roads in the off chance it misfired.

I ended up buying a new 2023 GLS 580 instead, and couldn't be happier!

Hope they are able to figure out the issue with your car.

Merlz

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Yes, it was always the same 3 cylinders, and yes it would happen rarely at low or no throttle, when coasting to slow down for example, but usually happened under throttle load when accelerating.

I hope the dealership was able to fix it before selling the car onto the next unsuspecting buyer.

Katie22

So I changed the spark plugs on my AMG GTC. I had the misfire problem. I ended up replacing the spark plug boots on each coil and made sure to carefully apply the insulating grease around the boots where they go on the coils and where they go on the spark plugs. From that point on I have not had any misfires. My car also would misfire under load which makes total sense since electricity always takes the path of least resistance. Since under load the cylinder pressure goes up from the turbo the electricity is likely shooting through the spark plug boots.

WRC-LVR

Yes indeed..many folks change the plugs and dont think to use the spark plug boot release on the inside of the boots, It also helps to put a little bit on the ribs of the plugs. I had a 2004 Ford escort station wagon that would always misfire when stepping on the gas ( load ) . Multiple plug changes did nada. New wires worked for about a week..Finally put new wires in and used the grease...wala no misfire again..ever...

You can check the plugs to see if you see any grey tracing running down the ceramic from the metal connector tip. Also check the inside of the boots to see if you can see any trace of arcing....

Be careful to use only a little bit inside the boot and dont get it on the metal connector tip of the plug

DaveW68

It could potentially be bad coil packs. I got a dreaded misfire a few months ago (bad enough to put it into limp mode under acceleration) and a new coil pack fixed it.

Katie22

It could be coil packs HOWEVER one can rule this out by changing coils to different positions. Also bare in mind that statistically coils are a LOW failure item. Of course when people change them sometimes the problem is solved. What they dont realize that that the new spark plug boot on the new coil was REALLY the problem in the first place........... and of course the coil boot costing around 10 dollars is a lot cheaper than replacing the coil with a new boot on it.

jd cruz

In the fire triangle there are 3 compositions of fire, the Air, Fuel, and Igniter/Spark. Removing one of these will sure make the fire misses..

Jumping into conclusions without determining real cause will cost a lot. Changing coil packs, coil boots or spark plug but still experiencing misfires?

I suggest to determine the problem first. Try using a good car scanner.

I personally suggest YOUCANIC scanner. Its easy to use, affordable and can help you find all things needed for your car.

Once you've scanned, the codes will help determine where the problem is coming from. It can be from Air system, Fuel System, Ignition System, Electric System, Engine Timing or Vacuum Leaks.

The solution was based on observation made by the scanner. A good car scanner will be a big help with engine misfires and a lot of troubleshooting needed for your car.