Greetings,

2015 ML350
Vin: 4JGDA5HBXFA514261
Bought 1/2018 with 15K miles, currently at 69K
Dealer Serviced

I have a problem that would only happen occasionally but now seems to be getting more regular. When the car decelerates quickly and then resumes speed, the engine starts to miss / buck, and the check engine light comes on. If I stop and turn off the engine briefly and then restart then all is usually ok, but the engine light will stay on for a while. This occurs when slowing down for a speed-bump, slowing down to merge into traffic, in rush hour stop and go. Again, it is when I stop more abruptly than a normal slow down such as for a stop sign. Recently I got the car scanned at AutoZone and it came up with code P0303??

Guess I will schedule with the dealer but wanted to get some thoughts in advance. The dealer recently upped their hourly rate to $210 - - ouch . . . . . ultimately would like to find an independent shop in the area but they are few and far between. Does anyone have an inde recommendation in the Md / DC area?

Any thoughts would be appreciated.

Paul/

 

Misfire on cylinder #3 is what a cursory Google search shows. I'd start with spark plugs. Pull them and look for issues. They need to be changed anyway if it hasn't yet been done. Check your spark wires while you're in there, then you can swap a coil pack for #3 and see if the problem follows the pack or not. Could be a clogged injector too, but I'd still start with the spark system.
Oh, and get yourself a proper scanner. They can be had for less than $200...

 

You said the car is dealer serviced, do you have the receipt for the 60K service? It should include spark plugs, transmission service, and brake flush.

If the spark plugs were serviced using MB protocol, the intake and a few parts were removed. Hopefully, they were put back together carefully, and correctly.

When following @rapidoxidation advice be careful to notice loose/improperly connected or damaged parts as you get deeper into the process.

 

Thanks for both of your insights. Will poke around and see if anything is obvious with #3. (and check on getting a scanner). Have not had the spark plugs replaced. I did go ahead and schedule an appointment with the dealer for next week and they will surely suggest new plugs. Best/ Paul/

 

Wanted to follow up from the dealer visit.

Engine Miss / light: it did turn out to be the ignition coil for plug #3. I guess the jolting caused the short or whatever, and it just got worse from there.
Labor: $322
Part: $108

Also had them reseal the front cam gear covers as they had been leaking for some time, and oil was dripping onto the other components, particularly the alternator. Ironically my last car (non MB) had the same issue that the dealer kept trying to fix under warranty, and did fry the alternator at big $$, so didn't want to get into the same situation. FYI on pricing.
Labor: $967
Parts: $572

Comparing the part numbers that the dealer charged with what can be found online is eye-opening - - - -certainly worth a DYI if you have the skills and tools.

P/
.

 

First and foremost, I am glad your vehicle is back on the road . A bit on the pricey side, but the problem solved .

Thank you for the heads up on the cam covers reseal prices, . Once I see mine leaking, I will schedule a weekend for that work. Not a chance $1500 for it.

Now to my dark side. The car was serviced around 60K miles, correct? and the car had never had any engine issues such as misfiring, hesitation, etc, correct? Wonder if someone may have "mispulled" the coil during servicing. Plug 3 is on the easier side (air filter side), but we MUST always be careful when pulling these M276 coils. They tend to stick a bit on the plug, and if you mishandle them when pulling they may get damaged. I have had close encounters , but nothing went wrong.

 

Yes, a bit pricey but glad it is resolved, and pleased to feel that I can drive it without concern of the issue. The diagnosis of a short in the coil does make sense; it has been happening over a few years (I bought in 2018 with 15K) only intermittently and in certain conditions, but recently it was occurring quite often.

All the best, Paul