Had a local mechanic replace all spark plugs on my E280. After picking the car realized vibration when I had to stop (car in drive) as well as when car is in park.
Were the new plugs not fitted properly? Did he damage the ignition coil?
Am taking the car back to him on Monday but would appreciate some responses to gain a better knowledge.
PS. Before taking the car in had no such vibrations

 

You are on the right track !
One or more cylinder may no longer have ignition.

The coils did not die overnight but the old fragile plastic connectors may have fallen apart.

The best shortcut is to use zip-ties on all of them instead of spend many-many hours to dolice in replacements.

You can expect a dash CEL and a fault code to get logged soon.
Of course all of this extra work should be on your dime. So quick zip tie hack welcomed relief.

Buy yourself a $150 OBDII LAUNCH cReader Elite Scanner to read ALL your car - Some faults stay more quiet without CEL: no getting surprised pays-off.

 

Thanks for the advice. The mechanic rechecked all spark plugs and the coils, all is good.
Problem of vibration still there. Feel it when the car is in drive (when standstill) and in reverse (standstill). No vibration at all when in park or neutral.
Could it be anything to do with mounts?
Appreciate any input.

 

It's possible that the new spark plugs aren't gapped correctly or weren't torqued to the manufacturer's specifications, leading to incomplete combustion and resulting vibrations. Additionally, if any ignition coils were disturbed or damaged during the replacement, they could cause misfires that contribute to the shaking. Another potential cause could be issues with the engine mounts, which might have been affected during the spark plug installation process, leading to increased vibrations when the engine is idling or under load. You should probably run a full system scan. There should be fault codes on at least one or more control modules related to this. You'll either need to take it to a mechanic, but if you want to figure this out yourself, then you'll need to get a full system scanner. The youcanic full system scanner is very good at diagnosing all systems, and there are other scan tools that can do this. Just be careful to use a full system scanner or you may scan the car and see no fault codes as some scanners can read all vehicle systems. youcanic can run an in-depth all system scan as well as diagnostics. I hope this helps.

 

you stressed that it was not there prior to service... so I understood it happened during service. Mounts don't go bad overnight.

Besides coils two collateral issues are associated with sparkplug job:

-1- the old coil boots are best replaced with plugs. They cause misfire.

-2- the old intake seals are best replaced when disturbed. They cause vacuum leak.

 

Very common. A good independent shop (forget dealerships) would have shown you the live smooth running values for your cylinders while the engine is idling. My techs have done that whenever I have had cars that have misfires/are running rough and suspicion turns to coil and spark plug-related issues, etc... You don't even need the Mercedes diagnostic tools for this. In my case, I have an Autel scanner capable of reading the live data and can see this myself. In the past, I have checked the live data prior to having the coils, spark plugs, associated wires, and/or injectors replaced. And, yes, I have gotten cars back from shops that subsequently had new, intermittent misfires...but I could identify them myself when running the live data tests with my own scanner and then confront the shop with the data... The scanners capable of doing this are quite affordable and worth it. I have also used it when shopping around for cars to purchase. If you know someone with such a scanning tool, see whether you can borrow it and check out your live data.

As for the plastic connector plugs from the wiring harness to the ignition coils, yes, they (usually, the retaining clips) always break with age... Based on my experience, Mercedes dealerships often don't stock the connectors for these older engines anymore, and they have to order them, which takes a couple of days to get delivered. Mercedes specialist shops used to keep spares around (they're cheap), but I find that many now neglect to do that... When their techs encounter these broken connectors (whether they broke them or the connectors had been broken already), rather than inform the customer and wait around for the part to come in, they just go ahead and zip-tie them down. Conscientious shops/service managers would at least note this in the repair record/invoice and inform the customer (my shop did that in one instance). Had the shop kept the spare connectors in stock, the tech could de-pin and replace the broken one literally in seconds with the right size tool...

 

I have never, not ever been able to replace plugs and not damage one or more of the coils. Not since my first MB in 2004....many since. It is the cost of ownership. BUT, the shop should have told you and been prepared for that inevitability.

 

Thank you everyone for your comments and input.
Since I am not into mechanics, I have forwarded all your input to the shop where the work was done.
Hope they do the needful.
Just for my knowledge, how much would a scan cost? Thanks

 

They will love that. Hey, if you go out for dinner this weekend tell off the chef before your food is made...........

 

Scanning the chassis is an integral part of troubleshooting. It just provides clues to focus on... like X-rays at the dentist.

Trust the shop to do what they do best.
🤞