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I could use some help on troubleshooting this issue.
I have a 2015 C400 that I've been driving around for a while that has lost a good amount of power on acceleration. I suspect the turbos have stopped working since when I floor the gas pedal, the car accelerates very slowly from what I'm used to. I'm not seeing any other issues and the car does reach highway speeds, but it just feels as the turbos are not working. No check engine light or any other codes pending. Seems like this just one day happened as the car was running perfectly.
Here is what I've done and I don't recall if this issue occurred before or after these repairs I performed:
Changed battery - I've heard that it's supposed to be programmed after it's been changed and I've also heard it's not a big deal if you don't have it programmed. I never programmed it after the change.
Changed cabin filter under the hood and both air filters.
Changed spark plugs.
I've been driving the car around in this state for a while now, but have a little time now and would like to fix this if I can and get the missing power back. Again, no check engine light or other codes pending and the car otherwise runs normally.
Thank you for any tips or suggestions that can help me solve this mystery.
I could use some help on troubleshooting this issue.
I have a 2015 C400 that I've been driving around for a while that has lost a good amount of power on acceleration. I suspect the turbos have stopped working since when I floor the gas pedal, the car accelerates very slowly from what I'm used to. I'm not seeing any other issues and the car does reach highway speeds, but it just feels as the turbos are not working. No check engine light or any other codes pending. Seems like this just one day happened as the car was running perfectly.
Here is what I've done and I don't recall if this issue occurred before or after these repairs I performed:
Changed battery - I've heard that it's supposed to be programmed after it's been changed and I've also heard it's not a big deal if you don't have it programmed. I never programmed it after the change.
Changed cabin filter under the hood and both air filters.
Changed spark plugs.
I've been driving the car around in this state for a while now, but have a little time now and would like to fix this if I can and get the missing power back. Again, no check engine light or other codes pending and the car otherwise runs normally.
Thank you for any tips or suggestions that can help me solve this mystery.
This issue started some time AFTER you changed the plugs?
As a free diagnostic step you could pull them and see what they look like. Google images is your friend on "reading spark plugs."
Your best bet is to get an OBD diagnostic tool that's capable of real-time logging of the sensors. Check your boost pressure, fuel trims, ignition retard, etc.
It is kinda weird you don't have a code, but sometimes these cars just don't throw them for low performance issues.
There are a myriad of sensors and control solenoids that could possibly be the culprit; you would be the first M276.8 motor I've heard of to have the turbos go bad.
First thing to check would be that the intercooler pipe hasnt disconnected from the intake causing all of your boost to "blow out".
Log of the items above would be most helpful if you have no other codes on the car.
This issue started some time AFTER you changed the plugs?
As a free diagnostic step you could pull them and see what they look like. Google images is your friend on "reading spark plugs."
Your best bet is to get an OBD diagnostic tool that's capable of real-time logging of the sensors. Check your boost pressure, fuel trims, ignition retard, etc.
It is kinda weird you don't have a code, but sometimes these cars just don't throw them for low performance issues.
There are a myriad of sensors and control solenoids that could possibly be the culprit; you would be the first M276.8 motor I've heard of to have the turbos go bad.
Yes, my best guess is this started happening after the plugs were changed. The plugs look fine.
I do need to look into getting a better OBD diagnostic scan tool so I can grab those additional logs. I will search on the forums for recommendations, but any suggestions?
First thing to check would be that the intercooler pipe hasnt disconnected from the intake causing all of your boost to "blow out".
Log of the items above would be most helpful if you have no other codes on the car.
Thank you. I will check on the intercooler pipe.
I'm going to look into getting a better OBD diagnostic scan tool. Any suggestions while I'm looking?
Do you have an aftermarket intake? There are air sensors on both intake boxes. Failing to plug one of those in may cause the low boost codes you are seeing.
There are also MAP sensors on the intake plenum. The JB4 install guide has a photo of where they are. I would double check nothing came unplugged when you did the plugs.
Since there are only two, may as well replace them both as you've suggested. I'll get those ordered. I took a quick look at the engine and the 28/7 sensor on top of the manifold is easily accessible. The 28/6 sensor which appears to be on top of the intercooler looks like it's going to be much harder to reach. Any easy way to reach that one without taking off the entire manifold?
Also, what types are screws are used for both of those sensors?
Since there are only two, may as well replace them both as you've suggested. I'll get those ordered. I took a quick look at the engine and the 28/7 sensor on top of the manifold is easily accessible. The 28/6 sensor which appears to be on top of the intercooler looks like it's going to be much harder to reach. Any easy way to reach that one without taking off the entire manifold?
Also, what types are screws are used for both of those sensors?
Almost everything in the engine is torx or etorx.
Probably a stubby ratchet with whatever that bolt is, is your only hope
Received the turbo boost pressure sensor today. Even using a stubby with a torx bolt attached, there is not enough space to work with. I can't imagine I'd have to remove the manifold just to reach this sensor. Is there a better way of doing this that I'm missing?
I've attached some pics with the sensor circled in red.
Received the turbo boost pressure sensor today. Even using a stubby with a torx bolt attached, there is not enough space to work with. I can't imagine I'd have to remove the manifold just to reach this sensor. Is there a better way of doing this that I'm missing?
I've attached some pics with the sensor circled in red.
Ok, I'll give you my take... But you aren't going to like it 😂
If you need the IC to move/shift you have to:
1) remove the intake/filter piping to the turbos
2) disconnect the intake pipes between the turbos and the IC(this is BY FAR the hardest part)
3) disconnect the IC from the throttle body
4) Pop the IC off of its retention bracket
After that the IC will move around quite a bit with only the coolant loop hoses connected.
Coincidentally, those are the first four steps of replacing the serpentine belt and tensioner assembly.
I guess I should have replaced that sensor while I was in there.
You're going to need a set of etorx swivel sockets to get the IC pipes out (or extremely low profile etorx wrenches).
Last edited by TwoC400s; Jul 20, 2024 at 11:36 PM.
Just as an update - for me it seems like it was just related to the map sensors.
The car finally threw a P0106 - Manifold Absolute Pressure out of range code.
As a first attempt fix I cleaned the MAP sensor on the intake manifold and the car ran way way better - power was back and the CEL went away without clearing the code.
Since then I have ordered both the sensor for the intake manifold and the intercooler (same part number) from Mercedes, and I am going to replace both.
The intercooler one was hard to get out, I had to use a stubby wrench with a Torx bit that I cut down to be very short, and it just fit. Would have been super annoying to remove the intercooler or intake manifold just to change that one sensor.
Just as an update - for me it seems like it was just related to the map sensors.
The car finally threw a P0106 - Manifold Absolute Pressure out of range code.
As a first attempt fix I cleaned the MAP sensor on the intake manifold and the car ran way way better - power was back and the CEL went away without clearing the code.
Since then I have ordered both the sensor for the intake manifold and the intercooler (same part number) from Mercedes, and I am going to replace both.
The intercooler one was hard to get out, I had to use a stubby wrench with a Torx bit that I cut down to be very short, and it just fit. Would have been super annoying to remove the intercooler or intake manifold just to change that one sensor.
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