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Yeah my scanner isn't up to the task. That part I recognized already and is part of why I scheduled the diag. My vacuum tester is just one of the little hand pump types. Not really much to go wrong there. It settles to zero when you lose vacuum and doesn't leak down on it's own. The gauge is also verified accurate against another standard non-pump type vacuum gauge.
Yeah I can rev it all the way out with no issues. I have linked a YT video of the behavior that I recorded last night after replacing the solenoid. I also pulled the negative terminal off the battery for 10 minutes right before to be sure the ECU was reset, and the behavior did not change.
Most symptoms of limp mode will limit your revs, since yours goes to redline then it is unlikely in limp mode. Welp, scheduled diag it is then.
not like this should matter but how is the condition of the aux battery (voltage coverter, capacitor on W205).
Last edited by W205C43PFL; May 1, 2026 at 09:14 AM.
Most symptoms of limp mode will limit your revs, since yours goes to redline then it is unlikely in limp mode. Welp, scheduled diag it is then.
not like this should matter but how is the condition of the aux battery (voltage coverter, capacitor on W205).
Agreed. I have a few things more to check while I wait for the dealer diag just to do my due diligence. I'm going to check the diverter valve diaphragms on both turbos and the large 3 port check valve in the throttle body elbow for boost leaks this evening.
My theory watching the boost behavior is as follows:
Only one turbo is down on pressure and likely leaking almost completely
I know this because Boost immediately jumps to exactly half as it should, and as RPM rises, the single functional turbo appears to try and compensate for the dead side, which tracks with what I know about how turbos work (more rpm = more spool = more boost potential)
I haven't checked the aux battery and in truth I don't know where it is yet...
Agreed. I have a few things more to check while I wait for the dealer diag just to do my due diligence. I'm going to check the diverter valve diaphragms on both turbos and the large 3 port check valve in the throttle body elbow for boost leaks this evening.
My theory watching the boost behavior is as follows:
Only one turbo is down on pressure and likely leaking almost completely
I know this because Boost immediately jumps to exactly half as it should, and as RPM rises, the single functional turbo appears to try and compensate for the dead side, which tracks with what I know about how turbos work (more rpm = more spool = more boost potential)
I haven't checked the aux battery and in truth I don't know where it is yet...
The aux battery is close to passenger glovebox activated charcoal cabin air filter. It is a good back workout 👍 but like I said unlikely the issue. I am not sure what your mileage is but turbos are very solid on the M276 really hope it is just a small issue instead but if not, that is premature. As long as turbos are properly cooled, engine oil changed regularly and at proper intervals, use quality engine oil especially those with esther based.
The aux battery is close to passenger glovebox activated charcoal cabin air filter. It is a good back workout 👍 but like I said unlikely the issue. I am not sure what your mileage is but turbos are very solid on the M276 really hope it is just a small issue instead but if not, that is premature. As long as turbos are properly cooled, engine oil changed regularly and at proper intervals, use quality engine oil especially those with esther based.
I bought the car with 83k miles on it with a full dealer service record. Since then I have put about 21k miles on it up to 104k with Motul 8100 X Max Change kits from FCPeuro every 5k miles.
My worry isn't necessarily the turbos themselves but the bushing on the wastegate flappers being too loose to effectively close all the way, and so far as I am aware, the only way to fix that at home is with a new pair of turbos, which I would likely pick up from Modalworks because they're cheaper for a pair than IHI or any other OE manufacturer and are a superior product with upgraded wastegate actuators, bushings, bearings, and come as new castings.
W212 M276 DELA 30 ; W211 M113k, W126 M117, W126 OM617, W211 OM642 ; R107 M117 X2, Sierra 1500 LZ0
Replaced my check valve, still running 0-60 in 5 seconds even with a eurocharged tune on my W212 E400. Amazing how my 22 year old E55 with 250K miles and 20 year old modifications doesn't need this sort of babysitting to maintain performance.
Replaced my check valve, still running 0-60 in 5 seconds even with a eurocharged tune on my W212 E400. Amazing how my 22 year old E55 with 250K miles and 20 year old modifications doesn't need this sort of babysitting to maintain performance.
Sounds like you're in a similar boat. Do you have the boost gauge coded into your dash? I bet you're in a similar situation to me...
I would be shocked if the turbos are "bad", especially both at the same time. Dealership may take that approach though because its easy $ for them and the price will be so high it wont be worth doing, so they get the $300 diag fee and wipe their hands of the work.
You have confirmed the coupling at the intercooler to throttle body is secure and not leaking?
Wonder if a vac line leak in the PCV system under the intake manifold would present itself like this. Enough vac loss under load that the wastegates dont fully close.
I have confirmed that coupler is not leaking, yes. My hose clamps were a little loose, but nothing was unseated anywhere. I tightened them up while I was in there and no change. As I stated a few posts back, there is that big 3 way check valve for PCV that could be bad right after the throttle body on that plastic intake elbow, or it could be a torn diaphragm on the diverter valves. Both of which I am going to check this afternoon. Hoping I find something before I need to drop it at the dealer.
It could also only be one turbo going bad based on the behavior. It could coincide with only one turbo doing most of the work. I'm an engineer by trade, just unfamiliar with platforms like this, so I'm picking it up quickly as I go along and trying to absorb as much information as possible.
I have confirmed that coupler is not leaking, yes. My hose clamps were a little loose, but nothing was unseated anywhere. I tightened them up while I was in there and no change. As I stated a few posts back, there is that big 3 way check valve for PCV that could be bad right after the throttle body on that plastic intake elbow, or it could be a torn diaphragm on the diverter valves. Both of which I am going to check this afternoon. Hoping I find something before I need to drop it at the dealer.
It could also only be one turbo going bad based on the behavior. It could coincide with only one turbo doing most of the work. I'm an engineer by trade, just unfamiliar with platforms like this, so I'm picking it up quickly as I go along and trying to absorb as much information as possible.
Was just confirming since the diagram outlines the intercooler inlet pipes but not the exit as leak source.
I would think that air volume to lose 7+psi going the wrong way through that check valve would blow apart the PCV and other fragile hoses. Also an engineer, but only know M276 platform from working on it over the years.
My money would be on the wastegate (s) not closing all the way.
Assuming you dont have JB4 on the car to see commanded boost target vs actual?
Was just confirming since the diagram outlines the intercooler inlet pipes but not the exit as leak source.
I would think that air volume to lose 7+psi going the wrong way through that check valve would blow apart the PCV and other fragile hoses. Also an engineer, but only know M276 platform from working on it over the years.
My money would be on the wastegate (s) not closing all the way.
Assuming you dont have JB4 on the car to see commanded boost target vs actual?
Unfortunately no, all I have is the factory boost bar as opposed to the full gauge. The car is completely stock other than some colored DRLs and a diffuser (for now, but I need it fixed before I tune it). 7 PSI would probably hurt some of the PCV components but I also don't know what crankcase pressure usually looks like on these engines. I know on a lot of boosted engines it can get pretty aggressive, leading me to believe the PCV system is probably designed with a factor of safety to handle a failure like that in the event of a ring failure and large amounts of blowby
I bought the car with 83k miles on it with a full dealer service record. Since then I have put about 21k miles on it up to 104k with Motul 8100 X Max Change kits from FCPeuro every 5k miles.
My worry isn't necessarily the turbos themselves but the bushing on the wastegate flappers being too loose to effectively close all the way, and so far as I am aware, the only way to fix that at home is with a new pair of turbos, which I would likely pick up from Modalworks because they're cheaper for a pair than IHI or any other OE manufacturer and are a superior product with upgraded wastegate actuators, bushings, bearings, and come as new castings.
Hmmm ya premature for turbo failure then even if it is those wastegate flappers you mentioned.
I suppose that's good to know, but it doesn't seem like too much else could be bad at this point. Maybe I should adjust the actuators if I can get in there? Though I've seen I shouldn't try that.
I suppose that's good to know, but it doesn't seem like too much else could be bad at this point. Maybe I should adjust the actuators if I can get in there? Though I've seen I shouldn't try that.
Couldn't hurt, I mean you did mention you are an engineer so you know what you are doing with expertise as well better than waiting sick for the appointment to find out.
W212 M276 DELA 30 ; W211 M113k, W126 M117, W126 OM617, W211 OM642 ; R107 M117 X2, Sierra 1500 LZ0
Originally Posted by Morflavo
Sounds like you're in a similar boat. Do you have the boost gauge coded into your dash? I bet you're in a similar situation to me...
I don't but can monitor boost with Torque or my JB4. I'm maxing out at 15PSI, which is higher than what a stock E400 should do, but it doesn't seem to come on until higher RPM. The car is sluggish off the line, but once it gets above 10-15, it goes like stink, but that initial sluggishness means it's hard to beat 5 seconds. A 1ft rollout on Dragy last night showed 4.65 seconds, which is the best I've done since I got the dragy, but I had to brake boost to 2K RPM to get it those numbers.
W212 M276 DELA 30 ; W211 M113k, W126 M117, W126 OM617, W211 OM642 ; R107 M117 X2, Sierra 1500 LZ0
Originally Posted by MatthewJ
Was just confirming since the diagram outlines the intercooler inlet pipes but not the exit as leak source.
I would think that air volume to lose 7+psi going the wrong way through that check valve would blow apart the PCV and other fragile hoses. Also an engineer, but only know M276 platform from working on it over the years.
My money would be on the wastegate (s) not closing all the way.
Assuming you dont have JB4 on the car to see commanded boost target vs actual?
I have a JB4 still plugged in that's leftover from before I put the eurocharged tune on, but it's running in map0 /disabled/pass through mode and I've left it simply for monitoring purposes. Can you clarify what values I should be graphing to determine boost target vs actual? This sounds like it would be extremely valuable in troubleshooting.
Couldn't hurt, I mean you did mention you are an engineer so you know what you are doing with expertise as well better than waiting sick for the appointment to find out.
Well, good news is my wastegates seem to have very minimal slop in them at all, so the turbos shouldn't need to be replaced. The drivers side diverter valve is good. I broke the plastic retainer ring on the PCV hose with that 3 way check valve so now I have that held in against the intake stream with a ziptie and need a new one... because of course. Passenger size diverter valve is a bit more of a ***** that I haven't been able to get to just yet, so hopefully that's an obvious failure point.
Well, good news is my wastegates seem to have very minimal slop in them at all, so the turbos shouldn't need to be replaced. The drivers side diverter valve is good. I broke the plastic retainer ring on the PCV hose with that 3 way check valve so now I have that held in against the intake stream with a ziptie and need a new one... because of course. Passenger size diverter valve is a bit more of a ***** that I haven't been able to get to just yet, so hopefully that's an obvious failure point.
Mistakes happen, don't be too hard on yourself. Oh good not a turbo issue but.... What is the problem then, back to the drawing board we go.
………..I broke the plastic retainer ring on the PCV hose with that 3 way check valve so now I have that held in against the intake stream with a ziptie and need a new one....
I think that your FIELD EXPEDIENT REPAIR will last a long time. No need to rush to fix it. Focus on the original problem.
You can ask me how I know.
I am still wondering about the MAP sensor.
The fuel system is very dependent on it and if the sensor gives an implausible value at higher boost levels then I would not be surprised if Mercedes just decided to limit the BOOST to fix the issue.
I bought a genuine Mercedes sensor and it wasn’t expensive and it was less than 5 minutes to change.
if you search on YouTube you will see that the diesel performance enthusiasts install a spacer on the MAP sensor to keep it away from PCV vapor and the Oil that gets caught up in the vapor. MAP sensors don’t like oil and fine particles clogging them up.
I haven’t decided that my E400 needs a spacer but I am thinking about it.
I think that your FIELD EXPEDIENT REPAIR will last a long time. No need to rush to fix it. Focus on the original problem.
You can ask me how I know.
I am still wondering about the MAP sensor.
The fuel system is very dependent on it and if the sensor gives an implausible value at higher boost levels then I would not be surprised if Mercedes just decided to limit the BOOST to fix the issue.
I bought a genuine Mercedes sensor and it wasn’t expensive and it was less than 5 minutes to change.
if you search on YouTube you will see that the diesel performance enthusiasts install a spacer on the MAP sensor to keep it away from PCV vapor and the Oil that gets caught up in the vapor. MAP sensors don’t like oil and fine particles clogging them up.
I haven’t decided that my E400 needs a spacer but I am thinking about it.
Good luck
Paul
I'll take a look at the MAP sensor. Should I jut use some electronics cleaner and see if that helps anything before rushing to replace it? That feels like a failure that the ECM would recognize and throw a code for
But my E400 had nothing and the MAP sensor was not functioning properly.
With the new sensor I can see the change in intake pressure as I depress the throttle.
Air rushing in and the pressure goes up
Throttle shuts and the pressure drops briefly below pressure at idle
Pressure stabilizes at the idle valve
If you are really handy with a wrench you might be able to get a T25 bit on the bolt for the sensor on the Intercooler and then you could swap the sensors.
The sensors on the Manifold sees the PCV vapors.
Having said that cleaning the sensor should be fine as well
I'll take a look at the MAP sensor. Should I jut use some electronics cleaner and see if that helps anything before rushing to replace it? That feels like a failure that the ECM would recognize and throw a code for
I am going to assume that you have a diagnostic tool that will show you live data.
Here is a picture of a throttle blip in my E400
Note: if your tool won’t graph the data then you can just watch it change.
Here are the key data points
1. Throttle open and air is rushing in and the pressure is approaching 100 KPa (My engine got to 87).
2. The throttle slams shut and the pressure drops below the idle value in my case 21 KPa
3. The engine gets back to idle and the ECU adjusts the throttle to get the desired RPM and the pressure is back to where it was at idle before the blip in my case about 31 KPa but it was bouncing between 30 and 33.
The tool that I used to make this measurement cost $81 on Amazon.
Note: you can also graph the pressure when the TURBO is boosting.
I think my stock E400 is somewhere around 180 KPa.
I am going to assume that you have a diagnostic tool that will show you live data.
Here is a picture of a throttle blip in my E400
Note: if your tool won’t graph the data then you can just watch it change.
Here are the key data points
1. Throttle open and air is rushing in and the pressure is approaching 100 KPa (My engine got to 87).
2. The throttle slams shut and the pressure drops below the idle value in my case 21 KPa
3. The engine gets back to idle and the ECU adjusts the throttle to get the desired RPM and the pressure is back to where it was at idle before the blip in my case about 31 KPa but it was bouncing between 30 and 33.
The tool that I used to make this measurement cost $81 on Amazon.
Note: you can also graph the pressure when the TURBO is boosting.
I think my stock E400 is somewhere around 180 KPa.
The C43 AMG will make more boost
Take care
Paul
Wow that looks similar to my pulse on a ECG.
Last edited by W205C43PFL; May 7, 2026 at 07:23 AM.
I am going to assume that you have a diagnostic tool that will show you live data.
Here is a picture of a throttle blip in my E400
Note: if your tool won’t graph the data then you can just watch it change.
Here are the key data points
1. Throttle open and air is rushing in and the pressure is approaching 100 KPa (My engine got to 87).
2. The throttle slams shut and the pressure drops below the idle value in my case 21 KPa
3. The engine gets back to idle and the ECU adjusts the throttle to get the desired RPM and the pressure is back to where it was at idle before the blip in my case about 31 KPa but it was bouncing between 30 and 33.
The tool that I used to make this measurement cost $81 on Amazon.
Note: you can also graph the pressure when the TURBO is boosting.
I think my stock E400 is somewhere around 180 KPa.
The C43 AMG will make more boost
Take care
Paul
gill, unfortunately I do not have a tool to do this with.
UPDATE: The dealer charged me half an hour of labor to tell me that the tech found absolutely nothing wrong with the car after plugging in and taking it for a test drive. I know something is still wrong however because of the below links I have uploaded. One is another C43 (2018, still a pre facelift), and the other is my car. The behavior and pull with the same throttle inputs is remarkably different, even though it shows no codes. My guess at this point is a boost leak somewhere. A friend of mine has a smoke tester that will pressurize the intake track to about 15psi, and I will be seeing him in roughly a week and a half at a car show. We will test it there! Until then, I'm not sure I'll have any updates considering the dealer thinks it's fine and nothing is wrong. Another possibility is that this is just what happens after 105k miles with an M276. I don't think that should be the case, so I'll keep hunting, but eventually I will have to give up without fixing it. If it wouldn't cost me 20 grand over my trade value I'd go buy that 2018 instead!
Unfortunately, the dealer has found nothing to be wrong. Xentry is showing zero errors or hidden limp modes according to the technician. The dealer is always frustratingly reliant on the computer to tell the tech everything. After looking through that thread you linked here, the only thing I can see is "test it with Xentry" and "Change the oil." Xentry finds nothing wrong whatsoever and the oil is only 4,000 mile old Motul X Max 8100. Neither of these things should be affecting me according to that thread. My only concern could possibly be a boost leak of some kind.
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