murchak

Hi all,

I have a 2014 E350 Regular Sedan with M276 DOHC engine with 74k miles. The 50k, 60k, and 70k recommended service was done at the Mercedes dealership. Spark plugs replaced at 60k miles, and transmission fluid done at 70k.
My check engine line came on a few days ago and it stays on, not blinking. The blue driver OBDS2 scanner showed a P0302 error code (which is cylinder #2 misfire). Below are my observations and things I have done so far.

1. Car idles fine (not rough) and no weird noises
2. Car doesn't seem to lose power at highway speeds - I have not noticed any power loss - perhaps a small amount (hard to tell)
3. I unplugged coil pack #2, the idle became very rough - plugged back and idle became smooth - this tells me that coil pack is okay, and so is the spark plug (remember the plugs were replaced with OEM plugs at the dealership at 60k)
4. I also swapped coil pack #2 with coil pack #1, and didn't see the error code change from P0302 to P0301. However, when I put everything back together, I got P0300 (random misfire) on top of P0302 error code

I am fairly certain spark plugs are fine as they are relatively new. I am also reasonably certain the coil packs are okay. What else is relatively easy to try at home before taking the car to a shop? My father-in-law suggested checking EGR.
I do not know how difficult it is to pull the EGR out and what kinds of test I need to do? Any suggestions? I read on this forum that another person had a similar issue on an M276 engine, and it ended up costing them a lot of money (about 10k)
as they had some kind of internal leak in the cylinder housing. I don't recall the specifics. Hopefully, that won't be the case with my car. Just an FYI - the dealership that did my service is in a different state, as I moved to a new state. So I can't go
back to the same dealership and have them check the spark plugs.

Thanks!

chassis

Check the ECU connector, cam position sensor connectors and cam magnet connectors for signs of oil.

MBNUT1

I have had a couple of misfire incidents triggered by cold starts. Either by it being pretty cold or by moving the car in and out of the garage but not warming it up. I would suggest clearing the code and see if it comes back since it seems to be running well. Another thought is an injector issue.

CaliBenzDriver

The boot extending out from the coils to the plug are known to be delicate items because the inards are made of resistive carbon instead of a coper wire.

Your contributing cylinder at idle is a great step. 👍

Did you reset the existing fault (Cyl#2 misfire) before ECU gave you a RANDOM misfire code??

murchak

Thanks all.
1. I do see signs of oil at the ECU connector. It also appears at the cam sensor location. See the attached pictures. What does the oil indicate?
2. I moved to MN and yes the engine misfire code started a couple of weeks after moving here in cold weather.
3. I attempted to clear the code, but the blue driver OBD2 scanner kept saying the vehicle does not allow clearing the code - I suppose this is because the car was running, so clearing the code wouldn't really remove it, as it would automatically come right back

The code was P0302 consistently for a while, but when I tried to swap the coil pack #2 with #1, then I got the random misfire. I don't know how to clear the code completely. Does the car need to be on for this to happen?

murchak

CaliBenzDriver

To reset ECU codes try "Key:ON but Engine:OFF".
When the ECU is busy running your engine, it can not take a vacation to restart itself.

If the Misfire fault follows your questionable coil after a reset, it will be solid evidence to inspect coil boot.

Oil leak inside connectors does not compare to oil leaks on covers. To check for oil contamination inside connectors you need to remove them ✌️

A simple car reboot may be considered at some point to help timing latencies.

murchak

I reset the codes with key in ON position with engine OFF. Then restarted the car and the check engine light did not come one. I used the scanner to read "check engine" codes and no code was read.
Not sure what to make of it at the moment. When I initially took out spark plug #2, I noticed that it did not come out easily. Maybe it wasn't set properly, but the car was running fine before.
At any rate, I did clean the air filter (blew away dust, and some debris that had gotten into the housing). I will be driving the car over the weekend and we'll see if any code pops up again.

Senecat

Your harness connections are dry. Bank 1 solenoid and cover is dry, Bank 2 doesn't look atypical or the root of any problem. The covers leak from the factory.

You have a vacuum leak or some unmeasured air issue.

chassis

Separate the connectors from the cam magnets and cam position sensors. Take photos and post here.

S-Prihadi

What is your short term and long term fuel trim at idle and typical cruising speed ?

Arrie

So this should be a direct injection engine with the high and low pressure fuel pumps. Other than electrical issues misfire can be caused by improper fuel injection, which can be caused by dirty injector(s) or improper fuel pressure at injection.

A point to possible injection issues is that the problem seems to have started after moving to colder weather area. Fuel ignition depends on atomization of the fuel at the injector and improper process of this makes it more difficult for the fuel to ignite. Cleaning the injectors is easy by using cleaner in the fuel for a few fill-ups. Fuel pressure is addressed by replacing the high pressure pump on top of the engine, which also should not be too bad of a job for a DIY.

Also, I understand the spark plugs need to be indexed in these FI engines. This should not be an issue as services were done at the MB dealer, but just saying.

chassis

@murchak Have you opened the connectors for the ECU, cam magnets and cam position sensors to check for presence of oil? The oil in the photos is leaking from the cylinder head covers, a common leak from the factory.

murchak

Thanks all. After my last post, the problem did go away for a while. I didn't have any check engine light come on. Also, the weather is now in the 60s - 70s so it is not cold in MN anymore.
However, yesterday, the check engine light came on again with P0302 code.
A few months ago, when I first noticed P0302 issue, the car would idle fine and I didn't feel any abnormality in idea or drive. When I physically disconnected spark plug #2, then the idle became very rough.
This told me that even if I have cylinder # 2 misfire issues, it is not because the plug is dead or there is no electrical connection between the coil and the plug.
Since the problem had disappeared for a while, I didn't end up opening the connectors for the ECU as suggested by chassis, to check for oil.
I want to try the next simple step or using some cleaner to put in my fuel tank to clean (possibly) dirty injectors.
What brand of cleaner should I use? How much of it should I put in a full tank? FYI - I always use ethanol free 91% octane in my car.
Should I use the cleaner for a few full tanks?

More importantly, if the error code is P0302 and I don't notice any idle issues or driving issues (loss of power, acceleration, etc.), does it damage to car in any way if I keep driving?
The dealership charges $180 just for diagnosing the problem (as do many other shops), and who knows what they will come up with and ask for thousands more to fix something.
I don't have or want to pay that much money, hence the reason I am asking for help from you kind folks! Thanks to all that read and contribute to this forum!

nc211

I don’t know how to do this, but if you can check your intake for signs of oil, that could be possibly be a cause too via a worn out PCV. My 2014 with 65k miles is getting a little oil pulled in to the intake and every now and then it’ll feel like a misfire stumble (and I can smell the oil.) Mine does it almost exclusively right at the point where the engine is about warmed up, like something adjusts to now compensate for being at operating temperature. It’s when the temp gauge is at the halfway mark with just a little more to go before hitting operating temp. My guys looked inside the intake and could see a very slight sign of oil in there, signaling the PCV is just about ready to be replaced…

I’ll also add, that in the past when I would do my own oil changes on my cars, about every 20k miles I would pour in some Seafoam into the oil itself and let the car idle for about 20 minutes to circulate it throughout and clean up the area where the oil travels. I’d let the car sit for an hour to drain down and cool, and then drain it out. The oil would be black as midnight every time. I’d sacrifice a quart of new to flush out the pan as well. All of my cars over the many years ran Silky smooth, and I’d notice a difference after the seafoam trick. Never cause me any problems. I’ve done it once on this Benz around 45k before gently driving it over to the shop for the oil change. It too smoothed it out a bit, but shortly thereafter I noticed the cam cap leaks, so not sure if they were impacted by it or not (I doubt it, as they leak in general it seems).

Rockster

For a fuel system/injector/engine deposit cleaner I have noticed a distinct improvement from an engine after running just a tank of Chevron Supreme (with Techron) through the engine. If Chevron (or Texaco or CalTex both are supposed to also contain Techron) gasoline is not available where you are you can buy Techron in a bottle off the shelf at your local auto parts store. Use according to directions.

Have to admit, with one car the gas tank capacity was 16.9 gallons. The label on a bottle of Techron indicated the contents would treat 20 gallons. I just dumped the bottle of Techron in the tank then filled up the tank.

It is a good idea if you use Techron out of a bottle to plan on an oil/filter service after the treated gasoline is (mostly) used up. The short version is Techron can add to the oil's contamination. (The Techron in gasoline is supposed to be a less powerful blend of Techron. The stuff out of the bottle, the black one, is more powerful.)

chassis

@murchak open the connectors for cam position sensors and cam magnets, take photographs and post here.

murchak

Updating an older post:

After using the Techtron fuel cleaner, I still get a bit of jitter at idle and my cylinder #2 misfire code is still there. This morning, I swapped ignition coil from cylinde1 to cylider2 and that didn't change the code.
Then I swapped the spark plugs between 1 & 2, and now not only do I get P0302 (as I did before), I also get P0301 (misfire in cylider1) and P0300 (random misfire). But physically, my spark plugs (cylinder 1 and 2) are totally indistinguishable.
I did have all my spark plugs replaced at the dealership at 60k miles, now car has 79k miles.
I called two dealerships to quote me for the cost of the ignition coils, and one said around $220/coil (part only) and the other quoted around $183.
On FCPEuro, I see the Bosch one for $52.99. Is there really this big a difference in the cost of ignition coil between dealership and FCPEuro? Something doesn't seem right. (here is the link to the ignition coil at FCPEuro https://www.fcpeuro.com/products/mer...sch-2769060501)

The car idles really nice, except every 4-5 seconds I feel a little jitter, and then it goes away, and then comes back, more or less on a regular interval. I don't notice any loss of power, or rough idle, or anything else. Could EGR valve be a problem?
Could I have vacuum leak anywhere?

juanmor40

Do you have an MB-aware OBD scanner? so the codes are more specific? P300 is generic for misfires (I usually see it when there is more than 1 cylinder with the problem), and P30x is a generic misfire for cylinder "x".

From your tests:
1 - Swap coils between 1 and 2 --> still fail at number 2 --> Coils might not be the problem , check
2 - Swap plugs between 1 and 2 --> now fail at both 1 and 2 --> nothing can be concluded since you have not cleared codes before restesting. You need to clear codes between tests so there is no history polluting your tests. However, it might be the plug is damaged.

The plugs seem identical? What are you looking at on the plug? The tip, or checking there is absolutely nothing strange from top to bottom. A minor crack on the porcelain (not obvious to the eye or covered under a stain) will easily trigger an arc from the plug to the head and get a misfire.

Plugs are cheap, and replacing only 1 just to be 100% certain that is the source is an inexpensive test. You are lucky the failing side is Bank 1, and not #6 on Bank 2 (PITA).

Also, I would no keep messing with #2 connector. Just replace #1 (assume the "failing plug" is still there). I personally avoid disconnecting, perturbing harnesses, connector installation in these vehicle as much as possible. A minor mishap you bent a wire (breaks internally), twist the ratchet wrong and crack the porcelain, etc. Uncle Murphy is always there to ruin a good effort.

chassis

https://mbparts.mbusa.com/oem-parts/...MtNWwtdjYtZ2Fz

$82/coil genuine MB part. Dealers are unethical in their walk-up pricing.

Replace coils. It makes a difference.

CaliBenzDriver

Coils are tough to kill even with poor GND, the rubber boot are just the opposite! At 80kMi not impossible but slim chance considering historical experience.
Just replace the 6 boots now and go blow the savings elsewhere... premium Amsoil

Use your scanner take a look hard look at your FUEL TRIMS under "hot idle rpm" conditions only.
What's your engine ECU reporting ?

murchak

1. Where do I buy the “rubber boots”?
2. Please see attached for fuel trims


the

CaliBenzDriver

Okay .... the ECU is forcing a lean mixture on your engine that's reportedly not burning well with active DTC.
I should address your intake temp sensor now, whatever causing your P00113 fault is involved to compute engine mixture.

I lean towards leaving your 20kMi old plugs alone undisturbed. Just good boots from your fav retailer.
I bet boots were conveniently not replaced with bare bone plug job .


We may soon have some homework to fix the poor GND circuit of your 6x ignition coils.... said misfire 🤘

murchak

Prior to today, I only had P0302 error code. Cylinder 2 misfire. This in fact was the very first error code that brought me to this forum. When I tried to move the coil from 1 to 2 (and from 2 to 1) then that’s when I got the additional P0301 and P0113 on top or P0302.

Is there any measurement that I can make on the coils (say resistance measurement) that can tell me whether the coil is good or bad?

MBNUT1

If you want to get a PhD in diagnosing M276 misfires start reading here:

https://mbworld.org/forums/e-class-w...-nighmare.html