Given that you’ve checked the spark plugs and air filter, and considering the symptoms you’ve described, it’s possible that bad fuel could be a contributing factor. If the fuel has been sitting for a while, it might have degraded, leading to poor combustion. Your plan to empty the fuel tank and refill it with higher octane fuel is a good move.
Additionally, since you mentioned the hesitation at low revs, it might be worth checking for any vacuum leaks or issues with the throttle body, as these can affect engine performance at lower RPMs. A sticky valve could also cause similar symptoms, so inspecting the valve operation might be beneficial.
If you haven’t done so already, running a diagnostic scan with a full system scaner like youcanic scanner to see if there are any fault codes related to the misfire or engine performance could provide more insights. Keep us updated on what you find, and hopefully, we can help you get your B200 running smoothly again!

 

The fuel would have to sit for quite a long time to go bad or stale.....at least 6 months I would suspect. Hope to hear that it's running better now.

 

just sharing screenshots the 3 fault codes I found within the ECM
P13C523
P030085
P030385

after spark plug change,

• cleared and no fault codes anymore on both ECM and TCM after a long trip
• hesitation/engine spluttering still happens when you press the accelerator hard while crusing in low revs
• no issue if you accelerate hard from standstill

will observe and test drive further this week, will update here after I have filled with fresh fuel and new air filter and new oil

 

still draining my fuel, down to half
new plugs, new oil, new air filter, topped up trans fluid, runs better and smooth, however I feel there is an air/fuel/spark mix issue that happens if I accelerate hard on the freeway (still stuttering/shaking/hesitating with no power response)

new observation:
I have plugged in my scanner, one function is about battery voltage.
After a 1hr drive on the freeway, I checked the voltage, I've noticed it is sitting around 12.5 volts even if I rev it high to 3000rpm, it may bump up to 13-14v after revving for a second, but goes back down to 12.5 (I will post the graph if I can)
my other vehicles normally sit at 13+volts when running
thinking if this is possibly a cause of the misfire (if not enough power is supplied to the coils)

the SAM also reports B1F4500, but I think this might be related to start/stop not working (Which is my preference) - so I'll replace it again with non-AGM to deliberately prevent start/stop, it will work while the batt is new, but after a few weeks, it will stop working (start/stop)
(battery is already 5yrs old)

I now also plan to replace the battery as it could be the reason why the voltage is only hovering at 12.5 (could be alternator deliberately preventing it) possibly causing misfire (just a guess)

thoughts from anyone?? I read a few places that a bad battery is a possible cause.

 

new fuel in (drained and filled up with 98 octane as usual)
new spark plugs (bosch)
new engine oil
new airfilter
battery charged up/restored (still to be changed)
hesitation issue still happens with deeper throttle inputs

car starts fine, idles fine, drives well with gentle acceleration

if you prolong the hesitation (by not letting off the gas when it hesitates), check engine will get triggered with a misfire, and in the 2x it happened, both instances pointed to cylinder 3

given I have already changed the spark plugs on all 4 cylinders, I will now replace the coil on cylinder 3 and see if that fixes the issue (about ~85 aud / 55usd for a Bosch)

 

Root cause of issue confirmed: Coil, Coil Leads insulation to be specific

I re-inspected coil #3 while waiting for new part to arrive and noticed small burn marks where the coil and the leads/tubes join, see photo

edit: photos uploaded below

for comparison, this is cylinder 4 (no misfire), but reviewing the photos now, I dont know if that black mark is a burn mark or not:

to confirm, I wrapped plenty of electrical tape around this joint (to prevent it from arc'ing), put it all back together, went for a test drive, and issue is resolved!!! 🎉

it is a bit of work to get to the coils, so I am contemplating if I should change all coils next time I get all of the tubes/connectors/intake pipe out. I will have to disassemble all the parts to get to the sparks/coils.

thinking: other coils may also have this issue developing.

OR I could just install the new coil and put tape around this joint on all the coils as prevention. just remains to be seen how long electrical tape will last against the heat of the engine.

1 Bosch Coil on order, I am waiting for it to arrive, Part number: 0 221 604 036 (or MB A270 906 05 00)

other thoughts:

• wonder if MB dealer changes all coils when they change the spark plugs? anyone?
• I can see evidence of water getting into the coil boots, so I really dont like doing an engine wash on this, not sure if this is a contributing factor
• the engine cover surely contributes to the heat being trapped on top of the engine, causing all these parts to wear out a little quicker (I might just remove the top cover)

hope this post helps someone out there.

 

Top dot # 1..Can't imagine any dealer changing the coils with a spark plug change.

Can you imagine the bill put in front of the client if you told them ..well we descided to just change all of the coils at the same time as your regularly scheduled spark plug change.

What labor and coil price do you think that would add to an already costly spark plug change ? If all coils are going bad, then there should be a recall coming...but I don't think that's the case at this time.

 

thanks @DEVOURS , yep can understand from the dealership perspective, customers will not like a higher bill than necessary.

but for us/me DIY person, at AUD$80/$55USD per cylinder, maybe a small price to prevent this happening unexpectedly? I'd expect dealer will charge 2-3hrs of labour for this.

 

Nice trouble shooting and good description of your work. Are you going to try and upload the picture again? I recently changed my sparkplugs and I curious to see where the burned area is. Lugging the engine like you described may be the culprit as it might be putting the cylinders in a condition that requires higher voltage than average to fire across the sparkplug gap. The connection wires to cylinder #3 may be the weak link in the ignition chain.

That's my WAG (Wild Ass Guess)

Baba Louey

 

Nice trouble shooting and good description of your work. Are you going to try and upload the picture again? I recently changed my sparkplugs and I curious to see where the burned area is. Lugging the engine like you described may be the culprit as it might be putting the cylinders in a condition that requires higher voltage than average to fire across the sparkplug gap. The connection wires to cylinder #3 may be the weak link in the ignition chain.

That's my WAG (Wild Ass Guess)

Baba Louey

hey @Baba Louey , thanks , and yep I saw your B250 spark plug change post (after I posted my B200 spark plug change story, I believe it should be a very similar process)

photos updated on my post above. keen to hear if you see anything similar in your coils

yep, it's possible that I haven't changed my spark plugs on time (68k kms) and they way I drive it (torquing on low revs) causing the coils to overwork and find a path somewhere else.
The plugs I removed were not too bad, the gap is a bit wider than spec but not by much (from memory)
I think moving forward I might just change the plugs at 40k kms (given I drive this car short distances = more operating time to reach 40k than someone who drives on the highway regularly)

I am also just thinking, my other vehicle (a honda) with double the kms/miles, calls for spark plug changes every 100k kms, doesn't have any issue with the coils so far, it is now close to 200k kms - just thinking out loud
the coil design might be better, no joins/bends - but on the other hand, im sure there are other W246s out there with double my mileage/kms with no coil issues
(I am only at 68k kms and I use this B much less)

I reckon bosch can improve this coil by extending the insulation further up a bit - wonder if anyone has a spare/broken coil if they can open it up.

I am thinking I might keep my coil with electrical tape as spare in the boot, can be used for future trouble shooting

anyway, resolved! and learned something new (for me)

 

..and you have helped every other member here who might develop a similar problem...Good eyes and great work !

 

just to close this post, it is confirmed resolved.

Bosch part arrived from an online shop (confirmed it is authentic using the Bosch code on the box)

Took out all 4 existing coils and added extra insulation using a few loops of silicone tape on all 4 coils (old and new)
(it is like JB weld Fuzetape, but a local brand Dynagrip, good insulation and can stand heat up to 260 C/500 F)
photo below.

Used the car with a few full throttle runs and no more hesitating, misfires gone. RESOLVED!

I have also observed that there MAYBE a better part out there, and with same part number, I found this on ebay with what looks like better insulation than what is in my vehicle, so maybe Bosch has improved the part.
But it seems to be for a CLA200 C117 X117 1.6 M270.910 (there seems to be differences which doesn't match the B200 part that I have but it may also fit)

Hope it helps someone out there in the future!

 

Thanks for this added new info...it will make a difference for others here. Your clear photos also help a lot.

 

Reading the last couple of replies made me remember that the service manual called for dielectric grease to be applied to the sparkplug boot and also I believe where the boot attaches to the coil. This grease should help stop the coil from grounding out.

Baba Louey

 

I can't remember ever seeing dialectric grease on the boot attachment. I would think that that instruction would be included somewhere on the coil or on the new boot...Just never seen or heard of that instruction.... or any accompanying tag requesting it..

Can you find that in your B W246 manual perhaps..?

 

From WIS (Workshop Information System). "Grease rubber lips (3) of spark plug connectors (2) using sparkplug connector grease before installation". There is no mention of putting the grease where the coil plugs into the spark plug connector so I was wrong there. The manual calls it spark plug connector grease, MB part number A 002 989 80 51. I assumed it was dielectric grease which I had in my tool box.

Baba Louey

 

Yes, it would have to be dialectric grease. I also have a tube that I rarely use except on smaller contacts in the past. Great note found by you.

When changing plugs and wiring and connector caps/boots over the last 50 years, I've never seen any dielectric grease ever in use.... but have any shops been using it after all ? That is the $64,000 question.

 

Once a carbon track gets established (like down the side of a coil tower), it's pretty hard to stop the electricity from going to ground. I remember having to throw out a coil after it started to short to ground while driving in a snow storm. I wasn't a very happy guy that day.

I seem to recall Ford recommending putting a dab of dielectric grease somewhere on the rotor in the distributor. That was a long time ago.

Baba Louey