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I bought a used 2012 E550 coupe with the M278 back in December with 54k miles. I had lemon squad inspect the car for me and they found everything right engine wise.
Since day 1 It had rough idle that turned into random misfires on bank 1 and CEL on so I got it to the dealership.
-1st visit they said I had bad gas. They said that spark plugs, fuel pump, injectors all look good. They drained the tank and let me drive away only to have the same misfires on my way home.
-2nd visit they said the spark plugs are fouled only in bank 1. They replaced them in both banks but I could still feel the idle being rough. The car was shaking left and right when at a stop or traffic light.
When I complained, they said “you didn’t have to tow the car when you took it from here, so we had it fixed and you broke it. It is an old car, it’s normal you have problems.” From then on I had AMEX deal with them.
So since I decided that the specific dealer is not to be trusted, I started researching myself. I replaced all 4 o2 sensors, not much of an improvement. Then I found that both my air intakes had big cuts on them. I replaced them and I saw big improvement but…
I could still feel that the car doesn’t idle right. It’s not shaking as before, but I feel the engine is not smooth as it is supposed to be and my MPG are awful. I have no CEL or any codes at the moment. The car feels strong, doesn’t hesitate. It’s only at idle that it feels that sth is off.
I have an attachment below at idle that shows fuel trims being high and the air pressure being low.
I used a smoke gun twice and didn’t find any air leaks. I inspected all the air hoses and still nothing.
What do you guys think? Where should I focus next?
I am about to take out the manifold in order to clean the throttle body and idle valve. Would a dirty TB explain the symptoms?
Last edited by Cris Kalas; 06-12-2021 at 09:32 AM.
If only remaining symptom is rough idle, could it be that engine mounts need replacing? While I haven't experienced it personally, I've learned to keep an eye out for it from this blog.
I read about the mounts going bad and that you can feel it when driving too, me is only on idle though. Also the fuel trims are way off which indicates that the engine isn’t running right.
My plan is to check the pcv first, then clean fuel injectors, and last take out the intake manifold to clean the throttle body and inspect gaskets.
Any ideas of other things I have to check? Anyone?
Originally Posted by mikefalz
If only remaining symptom is rough idle, could it be that engine mounts need replacing? While I haven't experienced it personally, I've learned to keep an eye out for it from this blog.
1. try smoke test for manifold leaks
2. Have injectors taken out and sent off for cleaning and flow + spray pattern
3. check the fuel pressure regulator for return to tank issues causing trim to go out of spec trying to adjust
4. replace pcv valve with OEM
why not just take it an MB dealership and ask them to diagnose what is wrong? You don't have to get the problem/s fixed by them but it would be a no cost way of finding out what the problem is.
No, I haven’t. Problem is still there. Now I have a code for rich mixture on downstream sensor bank 2.
After my last post, I tried a few things.
1). I replaced the purge valve. That is because on my scanner it looked like it opens too often, even on idle it was sometimes at 50-60 %. Thought it was stuck. No results from that.
2) I intended to clean the injectors but I realized it was a little too much so I took it to a different Benz dealership to be diagnosed. 5 days later they called me saying that they can’t figure out what it is and it’s an old car, so many things can cause that. 2nd Benz dealer who could not diagnose it.
3) Then I took it to the best Indy Mercedes shop in the area. The car had thrown no codes, it is just the high positive LTFT and the rough idle. The mechanic felt it right away when driving the car in the shop, he said “it feels like it’s correcting the fuel trim when you stop and it idles, a little shake is what you feel”.
After 1 hour of putting it through xentry tests, he said that he doesn’t see anything wrong in the engine and it must be the catalytic converters. The fact that both banks have the same more or less fuel trims is explained by both cats failing at the same time at the same level, which he admitted is very unusual. He said fuel trims corrected when he took out the post cat o2.
Finding a used exhaust for a E550 coupe with the M278 engine is hard. Not many cars were sold with the v8 turbo. New parts require about 3k. The mechanic isn’t making selling parts, he says bring the parts and I’ll charge 1-2 hours of labor. So he is not trying to throw parts on.
Since then…
I run a Techron fuel system cleaner in my gas tank hoping to see a difference. The fuel trims started improving and went down to +10% from +20%. Then, they slowly went up again.
Does this help anyone think of a possible cause?
Watching many videos of Tasos Moschatos on YouTube I started suspecting sth is off with fuel delivery. He talks about fuel volume and how this is sth different than fuel pressure.
Low pressure pump delivers 4.9 bar on idle (a little low,6-7 is the right), high pressure is at 120 bar. When cruising I get 180-200 from high pressure.
So, I thought a good idea would be to change the fuel filter (fuel sending unit) located in the tank.
My theory:
If fuel filter is pretty dirty, then not enough volume of fuel reaches the injectors. Even though the pumps work hard and build up the right pressure, the fuel volume is not enough. The computer tries to correct that by keeping the injectors open for longer (positive fuel trims).
Why is it worse on idle?
On idle, the fuel rail pressure is lower than when I’m cruising. Which is normal. That makes it even harder to have the right amount of fuel volume delivered to the injectors.
When I cruise, fuel trims go down from +20 to + 7.
Can this relate to the purge valve working a lot?
I think, yes. If the car doesn’t get enough fuel, then it uses the purge valve more often to compensate for the lack of fuel.
Any feedback on my theory?
I have an appointment next week to replace the fuel sending unit. I’ll keep you posted.
Thank you all.
Attached some pics from scanner See how the commanded equivalence ratio jumps to 2 every time the purge closes. Bank 2 reads 0 because I have the CEL on.
Very interested in seeing what happens after the fuel filter and assembly is replaced. Some fuel assemblies have been known to leak a little bit of the fuel back to the tank which would mimic that.
In looking at the data you posted, The LTFT on one bank is way different than the other bank. 19% on one and 0.2% on the other bank. the bank with 19% is not getting the same amount of fuel. Check o2 sensors, wiring for o2 sensors, cats for good air flow ( not collapsing ) intake leaks on that side or exhaust manifold leak on that side pre cats. You can try swapping the o2 sensors side to side to see if the problem then follows, but IMHo its better to replace them both
The fact it got a bit better with the cleaner might indicate lots of crap in the fuel system . Unfortunately it may have moved some down and lodged in the one bank
Did you fill up from a station that may have had more ethanol than normal in the tank?
Very interested in seeing what happens after the fuel filter and assembly is replaced. Some fuel assemblies have been known to leak a little bit of the fuel back to the tank which would mimic that.
In looking at the data you posted, The LTFT on one bank is way different than the other bank. 19% on one and 0.2% on the other bank. the bank with 19% is not getting the same amount of fuel. Check o2 sensors, wiring for o2 sensors, cats for good air flow ( not collapsing ) intake leaks on that side or exhaust manifold leak on that side pre cats. You can try swapping the o2 sensors side to side to see if the problem then follows, but IMHo its better to replace them both
The fact it got a bit better with the cleaner might indicate lots of crap in the fuel system . Unfortunately it may have moved some down and lodged in the one bank
Did you fill up from a station that may have had more ethanol than normal in the tank?
That’s interesting, I’ve never heard before of a leaking fuel sending unit.
I put a comment under that pic, it is 0 because I have the CEL on and when that happens it doesn’t read it. If I delete the code and take a new screenshot you will see that both banks have LTFT very close to each other.
I missed that caption under the photo. Sorry my bad eyes, these days,
Just to confirm; one of the fuel filters is part of the fuel pump housing assembly ? Several car manufacturers do this. Debris can be pumped into that and that reduces the overall flow. Problem is the entire housing has to be replaced as the tiny filter is not normally replaceable. the reduction in flow puts pressure on any organic type hose connector in the assembly causing minor leaks esp at high demand loads
Underground tanks that have e85 or e50 can be very contaminated with water and other water soluble junk. The contaminated fuel deposits out residues in the tank and throughout the fuel system. This was more of an issue several years ago. but...all it takes is one bad tank of gas with Ethanol. Some of the issue was traced back to rubber containing type parts in the fuel system being attacked and then depositing black sticky residue in the fuel system but that has been solved by the car manufacturers.
I forgot to mention that if it traced to the injectors, it may be possible to clean them by pulling them and sending out for that service at reputable companies. You would have to check if the MB piezo type injectors can be cleaned or if they are replace only
Did you remove the manifold. It sure sounds to me like you have some manifold leaks causing the low vacuum and lopsided fuel trims.
A small leak would be expected since the problem show up at low rpm. If it were a big leak, it would show up at higher rpm too.
Good point. He would need to log boost, which he can do. He also needs to observe the wastegate actuator rod for fast cycling and manually test to see if there is play in the flapper arm on both turbos allowing misalignment of the flapper( s).
indeed if boost doesnt build, and everything else is ok, then the engine will go momentarily be very rich as it will not have the anticipated air flow for the fuel.. If he does reach and stay at 14 psi for some time, then his problem may lie else where
smoke test or inspect for static leak!
It may actuate normally during driving but leak manifold vaccum when expected to be sealed around engine idle.
Bad mixture end-up throwing off ECU expectations. 😜
The old school way to check for intake leaks is spray carb cleaner around all the spots it could leak at. So basically you spray all gaskets. If that fails try all over the intake since we have plastic intake manifolds that can crack/break. Spray the throttle body too, or the general area at least. Spraying before the throttle can often help troubleshooting but it won't find leaks, it'll just alter the A/F ratio so I don't think I wouldn't bother.
If idle jumps up when spraying one spot, you pretty much found your leak. Just a quick blast of spray is all that's needed and it'll be obvious. Well, obvious on a non-computer controlled car because they are rough idling because they're lean and you just fixed it for a brief moment. If computer controlled then it's compensating for that, or trying to, but it cannot correctly compensate for it so you will still get some reaction. In your case it seems it's incapable of compensating so it should be obvious.
The intake is mostly inaccessible so if you strike out on the areas you can reach, then I guess I'd try a long 1/16" or so tube to try and direct the spray where you want. I have some 1/16" tubing and tape it to a wire, like a coat hangar, to get it in crazy places.
If it were me and spraying the easy spots failed, I'd probably use starting fluid and spray a good healthy blast under the intercooler to flood the area and see if it responds. Not ideal since I suppose there's a small chance it could ignite, but even if it did I can't see how that would hurt anything. I'd have no issue with a small explosion and/or small fire, but fyi if you are so I'm mentioning the remote possibility of it.
The main reason I'm posting is I had a similar issue once, with the rough idle, but it was battery related! How does the battery play a part you ask? Who frikkin knows but it does. When the eng is off the batt voltage was slightly low. I can't recall by how much, but it wasn't enough that I would normally consider it an issue at all. And since it started fine it was a non-issue imo. I only replaced it because it was >6yrs old and that's about when the oem batts start to give up the ghost, plus I read on forums, maybe this one, that a low batt causes a variety of weird issues, including rough idle. When idling the battery voltage is perfectly fine since my alt is fine, so how it can affect the car when it's running idle I have no idea. Well, I have one idea, which I noted at the end of the post.
The rough idle was not the only thing it did to me, it was simply the worst. At first it started misfire here and there, and only under certain conditions. Like on the freeway it would sometimes feel like one cyl was missing. Or idle would be a bit rough. This was random at first, but then it randomly got worse here and there until finally it idled so bad it was loping like it had a huge cam, if anyone knows what's like, but it was bad. It look more like it was parked at Inspiration Point if you know you what I mean. Being random it wasn't always the same but with time it happened more frequently and was worse when it did. So the day it was idling like I described above was when I had to do something right now.
It also gave me a CEL and code one day, saying cyl 7 misfire and that the coil was bad. Problem #1 is it was idling and running much worse than one one dead cyl can cause. I know this because I've tinkered with engines a lot, which included pulling plug wires just to see, and in various orders. Like ever other one in the firing order, which isn't too bad, or pulling them in order which is much worse. Whatever the case, it was far worse than one cyl. It also didn't give the code until it was pretty bad, so I'd imagine it could be like yours and still not give a code.
So I replaced coil 7, knowing that it wasn't the issue but it might have been part of the issue. It wasn't the coil and I ended up putting the oem one back on, now I have a new spare coil in the trunk which I wanted anyway so no loss except my time...
Check eng lights and OBD codes never work for me fyi. I either have a code and no actual problem, or a problem and no code. In this case both. One exception was ~2008 when I had a bad O2 sensor code and it was in fact a bad O2. So no code or whatever code you may get, is all but useless as far as I'm concerned.
The first sign of a low batt, for me, was the ECO function didn't work which was loooong before I replaced the batt. I was fine with eco not working and it's how it was when I bought the car in Mar '20. I just assumed it was broke and was happy it was. I only found out it was batt related because it worked after installing the new battery, then I read online that they do that. My assumption is it senses batt voltage is low and saves that info to say; "hey, don't eco stop or you might not be able to start again"? And apparently that saved info affects the idle and whatever bs issues I had, like the backup camera: Other people have noted that the backup cam is one of the things you might lose too, which did go on the blink for me. The new battery didn't help in my case and a few months later I lost my cam altogether. Now it just displays a black screen with the stupid yellow guide lines. Apparently this is a separate issue and also common. It involves taking the trunk lid liner out to access it, which is a pita so I haven't done it yet.
My theory is it's programmed to cause non-battery related issues so you bring it to the dealer and pay mass $. I've also read that people have taken their low batt mystery issues to the dealer, who replaced various parts in their effort to "fix" the car. It's a known issue and no doubt daily one at the dealer, so they're F'ing people out of $. At the very least they'll sell you a very expensive batt. I got mine at Walmart for ~$170.
So the first sign was the ECO, which happened an unknown time before Mar '20. The camera started to intermittently fail ~Jan '21. The rough idle started ~Feb-Mar '21. June 15th is when I replaced the battery.
So the Readers Digest version is; I suggest looking into the battery thing first. If it's older, or not a nice expensive one, or just slightly low on voltage for any reason, I'd replace it.
Then I'd go with the Carb Cleaner (leak finder) and see what you find.
There is also a small batt in the trunk of my car that is oem original (my car is a 2016 E550 Couple made mid 2015) so I'm surprised it works, but it seems fine. Apparently when that one gets low it won't bother you other than saying on the dash to stop and idle the car? I guess that's to charge it up but how is idling better than driving it? I guess many cars have the batt in the dash, just a smaller one.
Meanwhile, I also have a high long term fuel trim issue which averages +10%. I don't believe it's correct because I get excellent mileage and I've never had any issues with fuel being rich or lean unless I did it by mistake. So I believe my fuel is correct. My Torque is also off, by a much bigger %, so really I don't trust anything it says. Point being that I wouldn't assume it's correct and I'd keep an open mind about other issues. Like who would think a low static batt voltage could cause all the BS I had, yet it happened.
Fingers crossed that something here helps, but let us know. Especially let us know if/when you find the fix so others may avoid your pain. Thanks
So I replaced the fuel sending unit and got improved fuel pressure on the low pressure pump but that didn't change my high long term fuel trims. My mechanic insists that his diagnosis for bad cats is the way to go. He had suggested a new exhaust system.
Next thing I took the car to an exhaust shop. The mechanic there said there are no leaks and no problems with the exhaust system. Great! Who do I trust now? Exhaust has no signs of leaks and is very quiet.
After that, I inspected the turbo to see if it seals properly as some of you mentioned. At cold start, it wasn't sealing right. It was shaking and going back. I took off the boost pressure controller and cleaned it. Then, I started the car while it was at operating temperature, the rod came straight to the front and stayed there. No back and forth, no shaking. So, I'm not sure if the cold start is different or if I just fixed the boost controller by spraying it. I'll check it again on cold start tomorrow morning. The point is, before cleaning and after cleaning it, the boost I get is 0.6 bars max. Also, no change on fuel trims after cleaning it.
I remember the first time I used techron fuel system cleaner the LTFT went from +20% down to +10% while on idle only for a couple of days though. Then it went back up. When I used it again, it wasn't as effective as the first time. What do you guys think of that?
Also, when I first bought the car, it misfired on my first ride. I took it to MB dealership, they said the car had E85 fuel in and fouled spark plugs. If that was true, then the previous owner was using low quality fuel?!?
So if he did, can it be that carbon build up is bad in the engine? Can carbon build up on throttle body and/or valves have sth to do with the high fuel trims?
Again, STFT are close to 0, the computer does its job for adjusting fuel trims and brings the LTFT at around +20% on idle in both banks. While cruising, LTFT go down to ~+8%.
Did the Exhaust shop guy actually pull the exhaust off to see if the pre cats or cats show signs of clogging? is there any sounds of hissing whilst running? ( Not leaks ) . If he did not then doubtful of the diagnosis. Have the front or rear O2 sensors been replaced? These newer thin film style sensors tend to become slow to respond over time. If you have the original ones and have more than 50K , it may be time to replace them all. FCP Euro has the correct Bosch ones for the 2015 E550 M278 engine. Fronts are $109 each and rears are $32 each so less than $300 if you can install them yourself. FCP Euro has guarantee for life too :-)
If not, then budget ~$200 for the install from an Indy MB
For the low boost pressure, the turbo flappers to close off waste gate are known to have issue so that the flapper doesn't seat properly resulting in low or no boost pressure. Traceable to play in the actuator rod where it goes thru the housing and sometimes the flapper itself. Not sure but there may be only one fix for that, replacement of the flapper housing. Expensive since you would want to do both turbos. Might look at seeing if they can be rebuilt and the housing re-bushed for the flapper rod. There are posts one here somewhere describing the issue better and possibly a fix. Other known issues are the lines going from the solenoid to the turbo wastegates on both banks and other sensors both banks. Lots of heat in there, they can bake and crack slightly. i would also check any PVC valves and replace or clean as necesary as those may not be closing under boost pressure causing low boost.
Sounds like you may have had a dirty boost pressure solenoid too. BTW that rapid cycling can exacerbate the Flapper rod wear so its good you have seemed to fix that.
Regarding your comment on the poor quality fuel, that could cause injector issues. Steady diet of Techron for a few weeks could help that. Carbon build on back side of throttle bodies and intake manifold got much worse for the early direct injection engines as there is no fuel spray in ports or manifold to clean off the ports or anything else. Black gunk everywhere. CRC makes some products to help but not sure ho effective that is. There are after market parts to trap crankcase vapours from getting into the manifold too Helps to keep the intake tract clean.
Did the Exhaust shop guy actually pull the exhaust off to see if the pre cats or cats show signs of clogging? is there any sounds of hissing whilst running? ( Not leaks ) . If he did not then doubtful of the diagnosis. Have the front or rear O2 sensors been replaced? These newer thin film style sensors tend to become slow to respond over time. If you have the original ones and have more than 50K , it may be time to replace them all. FCP Euro has the correct Bosch ones for the 2015 E550 M278 engine. Fronts are $109 each and rears are $32 each so less than $300 if you can install them yourself. FCP Euro has guarantee for life too :-)
If not, then budget ~$200 for the install from an Indy MB
For the low boost pressure, the turbo flappers to close off waste gate are known to have issue so that the flapper doesn't seat properly resulting in low or no boost pressure. Traceable to play in the actuator rod where it goes thru the housing and sometimes the flapper itself. Not sure but there may be only one fix for that, replacement of the flapper housing. Expensive since you would want to do both turbos. Might look at seeing if they can be rebuilt and the housing re-bushed for the flapper rod. There are posts one here somewhere describing the issue better and possibly a fix. Other known issues are the lines going from the solenoid to the turbo wastegates on both banks and other sensors both banks. Lots of heat in there, they can bake and crack slightly. i would also check any PVC valves and replace or clean as necesary as those may not be closing under boost pressure causing low boost.
Sounds like you may have had a dirty boost pressure solenoid too. BTW that rapid cycling can exacerbate the Flapper rod wear so its good you have seemed to fix that.
Regarding your comment on the poor quality fuel, that could cause injector issues. Steady diet of Techron for a few weeks could help that. Carbon build on back side of throttle bodies and intake manifold got much worse for the early direct injection engines as there is no fuel spray in ports or manifold to clean off the ports or anything else. Black gunk everywhere. CRC makes some products to help but not sure ho effective that is. There are after market parts to trap crankcase vapours from getting into the manifold too Helps to keep the intake tract clean.
Thanks for the info.
1) all O2 sensors have been replaced with Bosch from fcp euro. That was my first guess almost a year ago. Nothing changed.
2) The exhaust shop didn’t take off the exhaust pipes. Just inspected it.
The MB mechanic who diagnosed failing cats put a camera inside the cats through the o2 sensor hole. He said everything looks fine in there but then again the problem goes away when he disconnected the downstream o2 sensors.
I just used a Techron and LTFT are down to 13% from 20s that it was before. Not sure what to conclude from that. And yes, you are right. Running Techron can only help the injectors since it is a direct injection engine.
3) I’m thinking of the CRC for the intake valves. It’s not hard to use it through the map sensor hole but my question is: can dirty valves and/or throttle body be responsible for the highly positive LTFT? Does it make sense to even try it?
Did the Exhaust shop guy actually pull the exhaust off to see if the pre cats or cats show signs of clogging? is there any sounds of hissing whilst running? ( Not leaks ) . If he did not then doubtful of the diagnosis. Have the front or rear O2 sensors been replaced? These newer thin film style sensors tend to become slow to respond over time. If you have the original ones and have more than 50K , it may be time to replace them all. FCP Euro has the correct Bosch ones for the 2015 E550 M278 engine. Fronts are $109 each and rears are $32 each so less than $300 if you can install them yourself. FCP Euro has guarantee for life too :-)
If not, then budget ~$200 for the install from an Indy MB
For the low boost pressure, the turbo flappers to close off waste gate are known to have issue so that the flapper doesn't seat properly resulting in low or no boost pressure. Traceable to play in the actuator rod where it goes thru the housing and sometimes the flapper itself. Not sure but there may be only one fix for that, replacement of the flapper housing. Expensive since you would want to do both turbos. Might look at seeing if they can be rebuilt and the housing re-bushed for the flapper rod. There are posts one here somewhere describing the issue better and possibly a fix. Other known issues are the lines going from the solenoid to the turbo wastegates on both banks and other sensors both banks. Lots of heat in there, they can bake and crack slightly. i would also check any PVC valves and replace or clean as necesary as those may not be closing under boost pressure causing low boost.
Sounds like you may have had a dirty boost pressure solenoid too. BTW that rapid cycling can exacerbate the Flapper rod wear so its good you have seemed to fix that.
Regarding your comment on the poor quality fuel, that could cause injector issues. Steady diet of Techron for a few weeks could help that. Carbon build on back side of throttle bodies and intake manifold got much worse for the early direct injection engines as there is no fuel spray in ports or manifold to clean off the ports or anything else. Black gunk everywhere. CRC makes some products to help but not sure ho effective that is. There are after market parts to trap crankcase vapours from getting into the manifold too Helps to keep the intake tract clean.
I am having a similar rough idling issue but no cel. Did you ever change the motor mounts or check the intake manifold? Does idle get any better in different gears?
06-11-2021, 10:17 AM
