C250d misfire and white smoke when cold

[Jon2021]

I have a w205 2015 c250d bluetec that I bought flood damaged. It has a very strange problem when starting from completely cold the car starts first time with no problem or issues starting and runs for the first few minutes just fine but then as its coming up to around 40-50 degrees it starts misfiring and blowing white smoke and a very strong diesel smell from the exhaust. The strange thing is that when the car is fully up to temperature this all completely goes away and theres no smoke or misfire and drives fine. It only happens as the car is starting to climb up in temperature from cold. The first few minutes of starting from cold it doesnt have this issue. Also have a nox sensor fault however im certain it wouldn’t cause the car to misfire or smoke. I have replaced the injector for cylinder number 2 as it has a fault stored in the ecu P026685 an independent merc specialist told me this is to do with the injector however this did not help in any way and the problem remains. Anyone have an idea what this could be ?

 

[XJ600]

As you say flood damage, I would suggest a compression check first, just in case it swallowed some water.

 

[CarFan79]

Did you have the injector taught in? The code on the injector needs changed with a xentry star diagnostics.

 

[Jon2021]

As you say flood damage, I would suggest a compression check first, just in case it swallowed some water.

Had that done already on the Mercedes star diagnostics all 4 cylinders were fine no issues with compression

 

[Jon2021]

Did you have the injector taught in? The code on the injector needs changed with a xentry star diagnostics.

The injector was replaced by a Mercedes specialist and he used the star xentry tool to code the injector in

 

[Jon2021]

Im just confused as to what ive missed? Surely if it was an electrical fault it would always be present or atleast intermittent but this problem only occurs when engine is cold left overnight next morning on start up it doesn’t misfire straight away but gradually as its building temperature it starts misfiring until completely up to temperature

 

[Tuercas viejas]

A comment or two'
First gray /white smoke is an indication of incomplete combustion.
Same as a 1960 Leyland diesel engine and your super dooper MB engine c/w electronic gizmos.

Yes, as the temperature goes up the fuel cannot be burnt due to a lack of flame propagation within the cylinder(s) so it comes out gray/ white---- "Mr Sitting Bill".
OK, first is there any significant amounts of petrol (gasoline) in the fuel ,that gives off an eye watering grey white smoke.
Next you need to do a base line engine check (as olde worlde as it is) and the first is compression or lack of it!
The most common cause of grey/white smoke emission is lack of compression.

A new turbo diesel engine develops about 400 psi on cold cranking. (Naturally aspirated 450 psi is considered good )
So, as it wears the pressure falls to around 340 psi and no significant smoke emission or hard extended cranking or starting is experienced.
The threshold is 320 psi.
Any pressures developed below that and you are relying on solely the glow plugs and not compression as a principal element for starting a fire.
I submit your engine starts well in a cold start situation because of the glow plugs are in operation.
As the coolant temp rises the glow plugs are automatically cut or just pulsed , and then you are running solely on compression heat and reflected heat in the block/heads.
Then out it comes the white smoke --
Get it up to full operating temperature and it will be fine, the latent stored heat in the engine carcass is aiding clean starts & firing .

Why not drop the engine temp down to about 50 plus dgf by shutting it off, and go for start as it cools . With the engine temperature decaying and the glow plugs out of auto activation you will get an extended crank time , and flooring the pedal will flood the cylinders aiding a start, and out will come grey white smoke as Indian smoke signals Col Custer!
An explanation to your problem. which I have experienced many times in more than 63 years of working in this business.
(Starting with my late dad as a little kid in his shop in Gloucester. )
Tuercas Viejas

 

[Jon2021]

A comment or two'
First gray /white smoke is an indication of incomplete combustion.
Same as a 1960 Leyland diesel engine and your super dooper MB engine c/w electronic gizmos.

Yes, as the temperature goes up the fuel cannot be burnt due to a lack of flame propagation within the cylinder(s) so it comes out gray/ white---- "Mr Sitting Bill".
OK, first is there any significant amounts of petrol (gasoline) in the fuel ,that gives off an eye watering grey white smoke.
Next you need to do a base line engine check (as olde worlde as it is) and the first is compression or lack of it!
The most common cause of grey/white smoke emission is lack of compression.

A new turbo diesel engine develops about 400 psi on cold cranking. (Naturally aspirated 450 psi is considered good )
So, as it wears the pressure falls to around 340 psi and no significant smoke emission or hard extended cranking or starting is experienced.
The threshold is 320 psi.
Any pressures developed below that and you are relying on solely the glow plugs and not compression as a principal element for starting a fire.
I submit your engine starts well in a cold start situation because of the glow plugs are in operation.
As the coolant temp rises the glow plugs are automatically cut or just pulsed , and then you are running solely on compression heat and reflected heat in the block/heads.
Then out it comes the white smoke --
Get it up to full operating temperature and it will be fine, the latent stored heat in the engine carcass is aiding clean starts & firing .

Why not drop the engine temp down to about 50 plus dgf by shutting it off, and go for start as it cools . With the engine temperature decaying and the glow plugs out of auto activation you will get an extended crank time , and flooring the pedal will flood the cylinders aiding a start, and out will come grey white smoke as Indian smoke signals Col Custer!
An explanation to your problem. which I have experienced many times in more than 63 years of working in this business.
(Starting with my late dad as a little kid in his shop in Gloucester. )
Tuercas Viejas

Thanks for your reply, the problem here is i have had a compression test done on both cold and hot engine temperature and it is completely fine on all 4 cylinders this is one of the first things i had checked before i started spending more money on it. Thing is with diesel even if the slightest bit of water is sucked into the engine it will cause it to hydro lock as there is such high compression in diesel engine compared to petrol/gasoline engines. Even the slightest bit of water in the cylinder head will bend a conrod and the car will not start. It has only done 50k miles and has had one owner from new the car is 5 yrs old. The compression test was carried out by a Mercedes specialist using the star xentry software and it is the same on all 4 cylinders. This is why im struggling to find answers because it seems so out of the ordinary and all the common things have already been tried and failed.

 

[Tuercas viejas]

Thanks for your reply, the problem here is i have had a compression test done on both cold and hot engine temperature and it is completely fine on all 4 cylinders this is one of the first things i had checked before i started spending more money on it. Thing is with diesel even if the slightest bit of water is sucked into the engine it will cause it to hydro lock as there is such high compression in diesel engine compared to petrol/gasoline engines. Even the slightest bit of water in the cylinder head will bend a conrod and the car will not start. It has only done 50k miles and has had one owner from new the car is 5 yrs old. The compression test was carried out by a Mercedes specialist using the star xentry software and it is the same on all 4 cylinders. This is why im struggling to find answers because it seems so out of the ordinary and all the common things have already been tried and failed.

Was this test done using a scanner and the crank test?
We call it a Lazy man's test?
If I/We get a suspect engine such as this in the shop ,yes it gets the quick lazyman's test, but if the issue cannot be pinpointed, then its glow plugs out, and physically test the engine with a gauge set .
Rule of thumb-- You are allowed 10% between cylinders and 25% variance across the spread.

I/We have just fixed two OM642 engines such as this.
One passed the lazy man's test, but failed the physical test with the best pressure reading of 192 psi on #2 cylinder, and it ran, but a "smoker" failing its E test .

The other which we rebuilt "in house" was caused by a bent rod (following a previous head gasket failure and coolant in the cylinder ,as you have mentioned) .
This diagnosis was confirmed by doing a leak down test, which briefly is done by introducing measured shop air into each cylinder via the compression tester hose & glow plug hole.
With an 80% leak down #1 cylinder, it got torn down to reveal , yes a bent rod and classic excess wear evidence one a piston flank.

The other overlooked issue is a cracked piston caused by fueling issues.
Running across the toroidal cavity, these cracks can penetrate the the crown.
The Mahle piston on most MB engines these days with under piston cooling have a cast hole on the underside to receive the under piston cooling spray, which is connected to a hidden cavity. Within the crown this cavity receives the full blast of oil and vents through the bore conformable oil ring set radial holes.
Again a leak down test will confirm if there are any compromised pistons .
Often if an engine is suspect on one or more cylinders, a bore endoscope with give the smoking gun evidence of poor combustion, because the crown will have a "wet" carbon look, whereas a perfectly running engine will have a carbon patina on it like a dusty black chrome finish, and the injection spray pattern will be evident on the finish as a series of round patches.
This is the first step to pinpointing the issue, the other is exhaust treatment issue , but you must rule out engine mechanical defects first.
Tuercas Viejas

We use for leak down test something like this:-

https://www.amazon.com/OTC-5609-Cylinder-Leakage-Tester/dp/B0030EVL60/ref=asc_df_B0030EVL60/?tag=hyprod-20&linkCode=df0&hvadid=312158556601&hvpos=&hvnetw=g&hvrand=300150738097212034&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9028757&hvtargid=pla-434422629493&psc=1

Petrol/gasoline engine is shown

 

[Jon2021]

Was this test done using a scanner and the crank test?
We call it a Lazy man's test?
If I/We get a suspect engine such as this in the shop ,yes it gets the quick lazyman's test, but if the issue cannot be pinpointed, then its glow plugs out, and physically test the engine with a gauge set .
Rule of thumb-- You are allowed 10% between cylinders and 25% variance across the spread.

I/We have just fixed two OM642 engines such as this.
One passed the lazy man's test, but failed the physical test with the best pressure reading of 192 psi on #2 cylinder, and it ran, but a "smoker" failing its E test .

The other which we rebuilt "in house" was caused by a bent rod (following a previous head gasket failure and coolant in the cylinder ,as you have mentioned) .
This diagnosis was confirmed by doing a leak down test, which briefly is done by introducing measured shop air into each cylinder via the compression tester hose & glow plug hole.
With an 80% leak down #1 cylinder, it got torn down to reveal , yes a bent rod and classic excess wear evidence one a piston flank.

The other overlooked issue is a cracked piston caused by fueling issues.
Running across the toroidal cavity, these cracks can penetrate the the crown.
The Mahle piston on most MB engines these days with under piston cooling have a cast hole on the underside to receive the under piston cooling spray, which is connected to a hidden cavity. Within the crown this cavity receives the full blast of oil and vents through the bore conformable oil ring set radial holes.
Again a leak down test will confirm if there are any compromised pistons .
Often if an engine is suspect on one or more cylinders, a bore endoscope with give the smoking gun evidence of poor combustion, because the crown will have a "wet" carbon look, whereas a perfectly running engine will have a carbon patina on it like a dusty black chrome finish, and the injection spray pattern will be evident on the finish as a series of round patches.
This is the first step to pinpointing the issue, the other is exhaust treatment issue , but you must rule out engine mechanical defects first.
Tuercas Viejas

We use for leak down test something like this:-

https://www.amazon.com/OTC-5609-Cylinder-Leakage-Tester/dp/B0030EVL60/ref=asc_df_B0030EVL60/?tag=hyprod-20&linkCode=df0&hvadid=312158556601&hvpos=&hvnetw=g&hvrand=300150738097212034&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9028757&hvtargid=pla-434422629493&psc=1

Petrol/gasoline engine is shown

Thanks again for your reply. Yes this does make sense i guess the very next step i should take is get a physical compression test done on all 4 cylinders through the glow plug holes, does it matter whether this test is carried out whilst engine is hot or should it be completely cold and left overnight?

 

[Tuercas viejas]

Thanks again for your reply. Yes this does make sense i guess the very next step i should take is get a physical compression test done on all 4 cylinders through the glow plug holes, does it matter whether this test is carried out whilst engine is hot or should it be completely cold and left overnight?

Well its usual to do it warm as clearances open up, but some techs still like to do it cold.
From a practical sense, I advise soaking the plugs in their pockets with in a solvent , like Plus Gas. (We use Kroil on this side .)

Kroil - The Best Penetrating Oil, Degreaser, and Fuel Additive

Kroil Original - The most trusted penetrating oil since 1939! Choose from Kroil Original Penetrant, Kroil Original Penetrant Aerosol FormAT (AeroKroil), or Silikroil (Kroil Penetrant with Silicone).

www.kroil.com

Get the engine stinking hot after a few days soaking, to avoid breaking them (glows) off in the head .

It will take" a few" to remove the plugs, so it will cool enough in the lapsed time to "ready the engine" for the test.

Once out, you can do the test writing the figures down on a fag packet .(Thinking of my late dad doing this with a 20 Woodbines packet. )
Do you have access to MB's glow plug cream ,(or should I write CREME ?) which you smear on the glow plug threads to prevent future thread seizure.
If you need the part number for this "MB face crème" I can get it for you, we have about three pots in stock .
Tuercas Viejas

,

 

[Jon2021]

Well its usual to do it warm as clearances open up, but some techs still like to do it cold.
From a practical sense, I advise soaking the plugs in their pockets with in a solvent , like Plus Gas. (We use Kroil on this side .)

Kroil - The Best Penetrating Oil, Degreaser, and Fuel Additive

Kroil Original - The most trusted penetrating oil since 1939! Choose from Kroil Original Penetrant, Kroil Original Penetrant Aerosol FormAT (AeroKroil), or Silikroil (Kroil Penetrant with Silicone).

www.kroil.com

Get the engine stinking hot after a few days soaking, to avoid breaking them (glows) off in the head .

It will take" a few" to remove the plugs, so it will cool enough in the lapsed time to "ready the engine" for the test.

Once out, you can do the test writing the figures down on a fag packet .(Thinking of my late dad doing this with a 20 Woodbines packet. )
Do you have access to MB's glow plug cream ,(or should I write CREME ?) which you smear on the glow plug threads to prevent future thread seizure.
If you need the part number for this "MB face crème" I can get it for you, we have about three pots in stock .
Tuercas Viejas

,

Hey yes please would be great if you can get me the part number i didnt even think about that, apparently removing the glow plugs is a hard job as they tend to get stuck in there sometimes due to the high heat they go through.

 

[Tuercas viejas]

Hey yes please would be great if you can get me the part number i didnt even think about that, apparently removing the glow plugs is a hard job as they tend to get stuck in there sometimes due to the high heat they go through.

OK la Crema del a Crema de las Mercedes .A 001 989 42 5110
It comes in what can be best described a "match pot" size.
Which when I lived in England (which seems like centuries ago now) was how you did mix and match paint at places like B&Q with missus .
Just a tip when pulling glow plugs.
I use 1/4" drive ratchet and socket so that you don't put to much effort on the plug & sheer it .
Caution! If it starts croaking like tree frogs, simply apply more penetrant & care turning it back and forth, without excess of zeal straining the plug to point where it might sheer !
All the best (Via con Dios )
Tuercas Viejas