P0300 only the dreaded random misfire

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Like the title says the recently purchased CLA250 4MATIC 2014 throwing this code but no others

Wife was on the way home from work .....stumbling and shaking she was able to get it about 1.5 miles to a acquaintances house until I could get up to see

Code reader only gives p0300 and the car does not store this code only when trying to idle smells fuely out the pipes

Did plugs and no coils at 100k about 6 months ago

Pulled the coils and went and got 4 Duralast coils from AZ as well as 4 new actual MB plugs from MB

Installed still same exact only maybe 5% better if that

Checked for obvious vaccum leaks with a can of carb cleaner very carefully when the engine was cold soaked this morning

No other codes that my simple Inova OBD2 will show .....did the alternator test and it showed good the car will idle better when forced to via foot pedal but still not drivable

If this were a timing chain issue do you guys suspect it would surely throw a code for that correct??

My next step is to see if possibly the EGR is clogged off or possibly the cat has plugged up but keep in mind this car was running perfect no chain noises no issues and this all hit while driving down the road ???

Tomorrow is a new day I may have to check a few more basics like fuel pressure and?? but it may also be time to admit defeat on my personal skill level with this complicated MB and have her towed to a euro shop

Thank for any quick tips I may be missing
 
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Pull the front O2 sensor and start the engine, if it runs better you know the cat is clogged. This may be hard to diagnose without MB Star diagnostics or a good scan tool, there are many possibilities.
No offence but using Autozone coils in this car is a bad move and will quite possibly come back to haunt you.
 

Braapdaddy

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Pull the front O2 sensor and start the engine, if it runs better you know the cat is clogged. This may be hard to diagnose without MB Star diagnostics or a good scan tool, there are many possibilities.
No offence but using Autozone coils in this car is a bad move and will quite possibly come back to haunt you.
Yes I kept the MB Delphi coils I do have a commercial account the manager should let me return or exchange for account credit I do plan on getting 4 from MB this was just a wishful attempt at a quick fix

My biggest question is why there are absolutely no other codes popping up or even the service engine light staying on..... it only blinks not solid and once key is in number 1 position codes ...... this eve I'm pulling it up on my car hauler and getting it home and having my buddy with a more advanced scan tool read it

Thank you for the oxygen sensor suggestion
 
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Fuel smell is your best clue. I would suspect fuel pressure regulator. Pull the plugs and see if they are wet with fuel.

EDIT: Next to look at is MAF (most likely) and TPS. AT 100k miles the O2 sensors are beginning to show their age and when I change them.
 
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Yes I kept the MB Delphi coils I do have a commercial account the manager should let me return or exchange for account credit I do plan on getting 4 from MB this was just a wishful attempt at a quick fix

My biggest question is why there are absolutely no other codes popping up or even the service engine light staying on..... it only blinks not solid and once key is in number 1 position codes ...... this eve I'm pulling it up on my car hauler and getting it home and having my buddy with a more advanced scan tool read it

Thank you for the oxygen sensor suggestion
A flashing CEL is the worst kind of CEL. It will be interested to see what else the scan tool finds.
 

Braapdaddy

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Here are the plugs that have nearly 6k miles on them and about 6ish months ...... look how clean the one on the far left is they were not wet or smelly when I pulled them
20220728_075445.jpg


The parts cannon has been fired round 1 so far I'm just 4 plugs and 4 Duralast coils I will go no further on parts until more in depth investigation can be done

One other note I left out it was a 110 degree day and has been for a few days
 

Braapdaddy

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Got it home on the car hauler today ....A friend who has a Snap On scanner is bringing it over tomorrow

He did say the basic scanner I have would not likely read many of the appropriate codes to diagnose

His first guess when I said CLA250 was jumped time I asked if this is an interference engine he said it likely is
 

Braapdaddy

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Yep, running rich. With no other codes I would suspect 3 bad fuel injectors.
Injectors I can handle my biggest fear is timing chain ..... if it is the chain the only thing stopping me from doing that would be the Mercedes/specialty camshaft tool 🔧

By tomorrow eve this time I should have it scanned
 
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Injectors I can handle my biggest fear is timing chain ..... if it is the chain the only thing stopping me from doing that would be the Mercedes/specialty camshaft tool 🔧

By tomorrow eve this time I should have it scanned
This engine uses Bosch direct injectors, it would be more than very rare to have one fail at 100K never mind 3 of them. If one fails and leaks there would be a white/grey smoke show, 3 leakers would probably hydrolock the engine. When a high pressure DI fails it is not a drip or runs rich, it is a flood.
Being a Turbo engine there may be a inlet/intercooler hose cracked, came off or broken, massive vacuum leak, failed MAF, ECM issue, other sensor issues or host of other things not only the timing chain.
I cant look at the engine but it must be diagnosed properly, do not start throwing parts at this thing, it can be very costly.
 

Braapdaddy

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This engine uses Bosch direct injectors, it would be more than very rare to have one fail at 100K never mind 3 of them. If one fails and leaks there would be a white/grey smoke show, 3 leakers would probably hydrolock the engine. When a high pressure DI fails it is not a drip or runs rich, it is a flood.
Being a Turbo engine there may be a inlet/intercooler hose cracked, came off or broken, massive vacuum leak, failed MAF, ECM issue, other sensor issues or host of other things not only the timing chain.
I cant look at the engine but it must be diagnosed properly, do not start throwing parts at this thing, it can be very costly.
Yes Sir understood no more parts until further investigation I have two 6.4 powerstrokes I am familiar with expensive 😀

If it is the possibility of the timing chain it has only jumped and not broken since it clearly will start

Do you know if this is an interference engine ??
 

D60

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I would at least visually inspect and clean MAF.....if nothing else because it's essentially free to do so

Rule out the simple, inexpensive fixes before deciding it's jumped timing
 
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Yes Sir understood no more parts until further investigation I have two 6.4 powerstrokes I am familiar with expensive 😀

If it is the possibility of the timing chain it has only jumped and not broken since it clearly will start

Do you know if this is an interference engine ??
MB has AFAIK not made a non interference engine of any sort in over 40 years. For the timing chain to jump it would be either long neglected tensioner which would have rattled like crazy and just ignored or a catastrophic immediate tensioner failure which would be very rare.
Don't hold me to it but I believe this engine (going from memory only) has enough valve relief in the pistons to accommodate a slight amount of chain wear aka stretch (chains do not stretch, they wear).
I would certainly check the timing but until I did I would be too worried about it. A quick and basic compression test will suffice in finding any valve train damage just pull the ECM fuse and all 4 plugs first, do it at WOT which should put it in clear flood mode anyway but if the helper let off the gas while cranking it will shoot fuel.
 

Braapdaddy

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MB has AFAIK not made a non interference engine of any sort in over 40 years. For the timing chain to jump it would be either long neglected tensioner which would have rattled like crazy and just ignored or a catastrophic immediate tensioner failure which would be very rare.
Don't hold me to it but I believe this engine (going from memory only) has enough valve relief in the pistons to accommodate a slight amount of chain wear aka stretch (chains do not stretch, they wear).
I would certainly check the timing but until I did I would be too worried about it. A quick and basic compression test will suffice in finding any valve train damage just pull the ECM fuse and all 4 plugs first, do it at WOT which should put it in clear flood mode anyway but if the helper let off the gas while cranking it will shoot fuel.
Hello Trav.....just ran the codes with my buddies Snap On
P0505
P1190
P2103
It did also show the
P0301 THRU P0304

There were a few about a headlamp and a rain sensor but this is the main list

I am just getting used to this scanner but I did run a test on the fuel and from what I can tell it's putting out around 2800psi

It idled very slightly better today as compared to yesterday
 

Braapdaddy

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Update after looking thru many of the settings and categories on the Snap On scanner I cleared every code and started the car .....same rough idle and blinking engine light

Now only codes are again the random misfire
And misfire cyl 2 and 3

Going to do as suggested and do a compression test
 
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Does it smooth out at all if the RPMs are raised? Idle air valve stuck open?

I had this happen on a family member's late nineties Buick. They tried to drive it on a long trip like that and the massive amount of fuel the ECU added to the mix over heated the cat to the point that most of the catalyst material blew into the muffler which in turn got so hot it melted the plastic wheel well cover and scorched the carpet in the trunk. From the picture, the muffler was an actual cherry bomb and was bright orange.
 
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Braapdaddy

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Latest update did a compression test on all cylinders .....cylinder 3 or the third from the left has zero compression all others immediately jump to 180 and hold

Strange was I swear one time out of the 5 or 6 times I tried this cylinder it also jumped immediately up but now I cannot replicate

So has a lifter collapsed ?
Here are my new MB plugs with literal minutes of run time from right to left
 
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