Flood water damaged c250d misfire and nox sensor fault HELP!!

[DrNick]

But both NOX sensors have been replaced...

 

[grober]

What about the exhaust temperature sensor and any software updates or the ADBLUE system or the SCR itself?

 

[Jon2021]

Yes both nox sensors have been replaced but i heard somewhere that apparently they need a software update in order for them to start working? I thought they were plug and play? And also those other systems you mentioned surely it would throw up a code if anything goes wrong with them ? The only codes i got was with the dpf being full of soot, nox sensor and the teach-in parameters of cylinder 2 being out of permissible range

 

[BULLITTBOSS]

Being in the garage trade for many years i have seen these symptoms many times i know a guy who used a car for many years with con rod damage, he purchased the car after being in a flood, we dried out the car emptied the inter cooler and intake of water and removed injectors,to remove water from in engine, got the car started, white smoke and slight misfire for about 30 seconds until warmed up, at which time white smoke disappeared, car pulled and ran well until cooled down then the same, we carried out a compression test and all were within limits, he ran the car like this for about 3 years then car overheated due to water pump failure, we removed the cylinder head, it was then apparent that one piston was lower than adjacent piston by about 2 mm we removed the con rod fitted a new one,reassembled engine and all was well,no more misfiring when cold no more white smoke,

 

[E55BOF]

Those aren't the OP's symptoms, though...

 

[Jon2021]

Yeah that doesn’t happen with mine though this is why its a strange problem. The car starts first time from cold absolutely fine with no issues or misfires at all. Runs and drives fine. After a few minutes of warming up it starts misfiring and only when it misfires it starts blowing white smoke. Sometimes you cant even see any smoke just a very strong smell of diesel. Then when the car heats up to temperature it all goes away, the smoke, the misfire and even the bad diesel smell. It only happens at around 40/50 degrees.

 

[MJJ]

I have definitely changed my mind since yesterday with the new info, and whilst I still think you have some electrical issues with the NOx sensors reading zero, I also now think there is some more fundamental mechanical issues underlying.

I know you don't want to hear this Jon, but looking at the data supplied so far:
- You have a car that you know has been flooded, and it is exhibiting a misfire plus error code on cylinder 2.
- Mercedes have published a workshop diagnostics document (I linked it yesterday) stating that excessive water within the intake will cause engine damage, and the same cylinder 2 error code you are seeing.
- You state that the car is not making the power you would expect, compared to a known good C220.
- @Bullitboss above shares a story of a similar scenario (agree, not exactly the same) with a hydrolock conrod failure small enough to keep the car running, but show similar symptoms to yours.

Personally, I think it is time to book it into a Mercedes specialist and get the cylinder head taken off. You will know for sure, and after replacement of the defective conrod, timing chain (sensible whilst you are in there) and water pump (similar), you should have a known good car with 100s of thousands of miles ahead of it. All for much less than your budgeted engine replacement.

Martin.

 

[MrGreedy]

Having slept on this, I was thinking just the same thing. The cheapest way to have a look at the conrod has got to be an option. I don't know if this has to be head off, or there is another way/tool/dropping sump that allows a 'cheaper' way of checking. But I think the bent conrod needs ruling out. Plus, even if it turns out not to be that, a major potential cause is ruled out and you have peace of mind.

 

[Petrol Pete]

It depends on the relationship (angle) of entry of glow plug or injector (that's if either go directly into the cylinder to give access to the top of the piston) but an accurate measurement to TDC might be possible through the hole. I have done it on engines before , but admittedly ones a bit more basic than what we are looking at now.

I have no idea how complicated your car is underneath , but removing the sump on many engines will give you some kind of a view up the cylinders . Even if accessible spotting a slight bend in a rod might be impossible.

 

[E55BOF]

There's a couple of misconceptions there, I think.

Firstly, the OP does not state the car is not making the power he would expect; he states it runs fine.

Secondly, it only misfires and smokes at a particular stage of warming up. Bullittboss references a car which only misfired and smoked until slightly warmed up; the OP's car doesn't do that.

Thirdly, a bent conrod wouldn't explain the Nox sensor problem, would it? I'd get that sorted first and take it from there before considering pulling the engine apart.

 

[MJJ]

Firstly, the OP does not state the car is not making the power he would expect; he states it runs fine.

Alas, this is what Jon (OP) said yesterday

And with regards to it running fine when warm, it runs great however you do notice that it is not pulling as strong as it should be. I had a c220d previously and that seemed to have more of a pull than this which is not right as this is a c250d.

 

[Jon2021]

Hi all, thanks for your replies. I think the main thing im trying to say is ive had a look at cars with slightly bent rods and how they sound and what the tell tell signs are and it just doesn’t seem to match mine. I know some of you have suggested that not all of the time u will get these signs but i just am struggling to come to terms with the fact the car is not displaying any obvious signs of internal engine damage surely this problem wouldnt go away when up to temp the car litterally sounds perfect when it is up to temperature not even the slightest knocking or misfire. Yes granted there is a problem with the power when it is up to temp but i have a strong feeling this is to do with the fact the dpf is full of soot and the nox issue. Furthermore i have had two new nox sensors already fitted but they are not reading anything. My guess is this will need updating which i will be doing straight away. As for the other problem I really am doing my best to locate a garage that actually does a physical compression test on this engine as i have had no luck so far called about 20 different garages. Some say the star xentry compression test is pretty accurate and some say its no good and needs a physical test. Im just starting to give up hope on this car at this point havent had much luck so far

 

[E55BOF]

So he did. However, it only misfires and smokes at a particular stage of warming up. Bullittboss references a car which only misfired and smoked until slightly warmed up; the OP's car doesn't do that.

Thirdly, a bent conrod wouldn't explain the Nox sensor problem, would it? I'd get that sorted first and take it from there before considering pulling the engine apart. Fix what you know is wrong before you start looking at other things that might be wrong.

 

[grober]

D

I have no idea how complicated your car is underneath , but removing the sump on many engines will give you some kind of a view up the cylinders . Even if accessible spotting a slight bend in a rod might be impossible.

THINK THE SUMP IS PLASTIC ON THE OM651?

 

[Brian220CDI]

Sump is plastic on my 220 om651. It's not an easy job to get the sump off as the steering rack and subframe get in the way. I did it a few months ago by dropping the frame as low as possible on the bolts and lifting the engine up with an engine crane on the front eye after undoing the engine mounts at the side.

 

[CarFan79]

A couple of things I'd recommend.

The DPF won't regen with a current fault, ie Nox sensors not reading any values. If possible have them taught in and if they start working try a forced regen. If they don't start working you need to find out why.

Quickest way to check for a possible bent rod is to remove the injectors and measure from tdc to a fixed point on the head/cam cover. Mercedes ask for this on the commercials and is mostly number 2 cylinder at fault.

A proper compression test is essential as the star diagnostics is not 100%. I had a sprinter at work that the star diagnostics showed no 1 & 4 cylinders down on compression. A proper compression test showed only no 2 cylinder being down.

 

[l5foye]

Hi all, thanks for your replies. I think the main thing im trying to say is ive had a look at cars with slightly bent rods and how they sound and what the tell tell signs are and it just doesn’t seem to match mine. I know some of you have suggested that not all of the time u will get these signs but i just am struggling to come to terms with the fact the car is not displaying any obvious signs of internal engine damage surely this problem wouldnt go away when up to temp the car litterally sounds perfect when it is up to temperature not even the slightest knocking or misfire. Yes granted there is a problem with the power when it is up to temp but i have a strong feeling this is to do with the fact the dpf is full of soot and the nox issue. Furthermore i have had two new nox sensors already fitted but they are not reading anything. My guess is this will need updating which i will be doing straight away. As for the other problem I really am doing my best to locate a garage that actually does a physical compression test on this engine as i have had no luck so far called about 20 different garages. Some say the star xentry compression test is pretty accurate and some say its no good and needs a physical test. Im just starting to give up hope on this car at this point havent had much luck so far

Why not buy a diesel compression test kit? There are many on the market .

 

[grober]

THIS MAY OR MAY NOT HELP as it deals with the early direct piezo injectors

https://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=757224

the injector /fuel rail hardware will be different but injection sequence on start up likely to be very similar

 

[Jon2021]

Hi everyone, just wanted to give you all an update in regards to my problems. I finally managed to get a compression test done and it turns out the compression in cylinder 2 is indeed low. Not sure what these numbers mean but if you guys can help it would be much appreciated. The figures i got on the good cylinders were all around 300psi(20 bar) and on cylinder 2 it was 230psi(16bar). This doesn’t seem incredibly low but is it enough to be considered bad? And to cause this misfiring problem? Thanks

 

[MJJ]

Hi everyone, just wanted to give you all an update in regards to my problems. I finally managed to get a compression test done and it turns out the compression in cylinder 2 is indeed low. Not sure what these numbers mean but if you guys can help it would be much appreciated. The figures i got on the good cylinders were all around 300psi(20 bar) and on cylinder 2 it was 230psi(16bar). This doesn’t seem incredibly low but is it enough to be considered bad? And to cause this misfiring problem? Thanks

I don't know what the Mercedes quoted specification is for compression on your engine (my previous gen E220d is 18bar/261psi minimum) , but generally speaking, you should have all 4 within 10% of each other. Remember that diesels rely *entirely* (glow plugs complicate slightly) on compression to heat the air in the cylinder and allow it to fire once diesel is injected. A lack of compression is almost certainly your misfire cause. I think the glow plugs are helping from stone cold, then when they extinguish, you experience the misfire.

I think you need to take the cylinder head off now, and investigate further unfortunately.

As per earlier comments, I also think you have a second issue which is the NOx sensors reading zero, and that likely preventing a needed DPF regen.

Martin.