I've read a whole bunch of threads about low boost on these cars and can't for the life of me figure out what is going wrong with mine. WHen I plant my foot, my boost gauge goes up to about half of the "max" bar when it used to go all the way. I figured this would be my check valve going bad again and I had one on hand so I replaced it. Sure enough the old one seemed to be bad, but replacing it did not solve the issue. My wastegate rods do not rattle back and forth at idle as would indicate an issue with those either.

The other odd thing about the behavior of the car is when I upshift, boost jumps from half to 3/4, but still wont go to full. What could possibly be causing this? Loose charge pipe maybe? I feel like that would be a no boost not low boost condition.

 

Check the check valve.

 

If you read my post all the way through, I did, it was bad, I replaced it, and the issue persisted. Hence the post.

 

Yes I read it but the reason I mentioned it again is because the new check valve might still be bad, where did you source it from? As far as I know, MB does not sell the check valve seperately and only sell the entire pump assembly. Aftermarket ones aren't always going to work.

What you could do is get a scanner capable of scanning Mercedes codes to scan the vehicle could also see if there is something stored, might be limp mode or it can be simply the intakes (check both passenger and driver side for leaks or if it wasn't clipped well).

 

I have an Autel Scanner. No codes found unfortunately. It seems the new check valve is still bad, assuming that I should be feeling nothing when I take the hose off and the vehicle is running. At idle, no oil sprays out of it, however I am getting puffs of air pulsing out of the valve. I assume this should not be happening and I need to order a better quality valve. Where would you recommend I pick one up? Or should I jsut buy a bulk pack on aliexpress/amazon and blow through them until one holds air?

 

I have an Autel Scanner. No codes found unfortunately. It seems the new check valve is still bad, assuming that I should be feeling nothing when I take the hose off and the vehicle is running. At idle, no oil sprays out of it, however I am getting puffs of air pulsing out of the valve. I assume this should not be happening and I need to order a better quality valve. Where would you recommend I pick one up? Or should I jsut buy a bulk pack on aliexpress/amazon and blow through them until one holds air?

 

I recommend that you get a vacuum gauge and you measure the actual pressure

Here is what I am getting


M276TT vacuum pressure at idle


I bought a handheld vacuum pump from Amazon that can also be used to bleed the brakes

NOTE: if you are not getting at least 15 inches of mercury from your check valve then you should get another valve or install a secondary check valve like I did

good luck

Paul

 

Sorry for the late reply, tell me what model you have, not all Autel scanners can read MB specific codes. I assume you already read this thread:
https://mbworld.org/forums/w212-amg/...ve-repair.html
Have a look at this as well:
https://mbworld.org/forums/e-class-c...e-upgrade.html
As for buying a check valve directly from pump manufacturer https://klifex.com/mercedes-vacuum-p...365-2762300265

 

Alright just got home from work and checked this. I am getting vacuum readings within one inch of mercury of what you're getting. I think it may simply be because the cheap check valve is junk and I will likely hollow one out and do the valve upgrade while I'm in there that was mentioned later in the thread. My wastegates are also holding at about 24" of mercury when I use the tester to check them. The only other thing I can think of is the boost control valve being bad. In which case, where is it on the engine? How hard is it to get to?

 

You could replace the entire pump but I guess try replacing the valve from the pump manufacturer first. As for taking it apart WIS might help.

 

your check valve appears to be fine.

I would look into something else

I will also reply to your question.

Thanks

Paul

 

The waste gate controller is easy to change.

I removed mine to inspect the built in filter (getting to the filter is a bit tricky)

NOTE: The vacuum leaves the controller and it is split into two with a Y pipe so unless one of the pipes is broken after the Y then it is unlikely that you have a waste gate vacuum problem


The valve is to the left of the reservoir for the inter cooler

Close up of the valve. I painted one of the vacuum lines so that I didn’t get them confused when I reassembled


I suspect that you have a different problem

Thanks

Paul

 

For my M276TT I had to replace the MAP sensor.

The original sensor had become very lazy and it made the vehicle very difficult to drive smoothly.

Mercedes decided to use two MAP sensors instead of using a MAF sensor.

I replaced the one after the throttle plate and I should replace the one on the inter cooler but I haven’t yet

Using my diagnostic tool I could blip the throttle at idle and the pressure would hardly change.


It is possible that you have a lazy MAP sensor


But there is another possibility.

The turbo charger is an exhaust driven turbine and a compressor for the intake air.

Up to now you have been focusing on the vacuum for the waste gate on the exhaust side.

But you should consider that the intake side has a diverter valve that will cut out boost by diverting the air back into the turbo instead of into the engine.

The diagram that Mercedes is using is no longer used by VW because of reliability problems

I upgraded one of my diverter valves to a DV+ to eliminate this problem (the other side is difficult to get to and I haven’t done it yet)

Here is the stock membrane that can tear and cause boost problems


Stock diverter valve membrane

good luck

Paul

 

Diverter Valve

Here is a video that explains how the diverter valve fails and what VW is using for newer vehicles.

 

@p_gill Did you notice any difference after installing the DV+ ? Was yours bad? I agree the VAG community was having a lot of issues with their diverter valves across different motors, but MB doesnt normally see this failure from what I see.
OP, if the check valve in the vacuum pump was bad for a long time, you can end up pushing motor oil through the vac system and into the wastegate actuators. When you removed the vac line at the wastegate actuator, did any oil come out?
On the MAP sensor, its not a bad item to check, you can also clean it with some MAF sensor spray and see if that helps. However, the lazy pedal seems to be normal function for MB cars, I would not expect to see a MAP sensor change on a fast peddle blip. You can watch the throttle position sensor also move slow compared to a fast pedal blip. Seems to be "lazy" by design.

 

I did not have any oil come out when I pulled it from the wastegate actuators, and both wastegates appear to move as designed, and hold about 25" of vacuum indefinitely when I put the vacuum tester on them. So those diaphragms are not torn. I think my boost pressure control solenoid is likely going bad, but I am not sure how to confirm this without changing the part and testing if that fixes the issue. I really hope to apply a stage 1 tune to the vehicle but I intend to make it function as designed stock first. This is both the first modern car I've ever owned and the first turbocharged car I've owned, so I'm trying to learn as much as I can about the diagnostics.

Tonight when I get home I will break out the vacuum tester again, put it on the wastegate solenoid, and check for any play in the actuator rod when in the "fully closed" position. If there is no play there, the conclusion must be the wastegate is not seeing enough vacuum to close all the way under full throttle condition. If that is true, and I am getting full vacuum to the control solenoid (which I am), and have no vacuum leaks in the system (which I do not), then that would lead me to believe that the controller valve is failing to divert enough vacuum to the wastegates to fully close, and therefore must be replaced.

My issue is unfortunately not just present only on a quick blip, and is present at sustained part and full throttle pulls in manual mode where I would typically see max boost.

 

I prefer the way the DV+ works which is why I switched to it. At very light throttle it makes the power output very consistent. The transmission in my Audi would lock up the Torque converter and the engine RPM would bounce around at 37 MPH.

For the M276 I like it but I don’t think it actually added any extra performance. Maybe a small amount.

The diaphragm in my stock Mercedes diverter valve was fine and I didn’t need to change it.


As for the MAP I will agree that the Mercedes Engineers did decide to dampen the behavior of the engine to make the driving experience smoother.

And I am not trying to get maximum performance from my M276 and I agree with the design intent of the engineer at Mercedes. (That is why I bought the E400)

But the response of my MAP sensor was so slow that it made the car difficult to drive smoothly. (If you step on the pedal and nothing happens then you will naturally press a lot harder and then quickly realize that you went to far)

The Map isn’t expensive and I bought it from Mercedes.

If I get a chance I will make a graph of the original sensor and the replacement. The difference is shocking.

Take care

Paul

 

Thanks for sharing this.

We skipped a step because we were assuming that you had already looked into the basic connections.

However since this is your first Turbo then step 1 is to make sure that you don’t just have a high pressure leak on one of the hoses.

A split hose would loose boost and create the type of problem that you are describing.


Check the red area


In the picture you can see two small hoses at the bottom of the inter cooler. A split in one of those hoses would cause a significant loss of boost


good luck

Paul

 

@p_gill I have done a test on the boost control solenoid and determined it is bad. Air flows out of the small tube if I blow lightly into the large tube in both positions after applying 12V, suggesting a torn diaphragm. I have ordered a new one from FCPeuro.

My wastegate actuators are open all the way at approximately 17" of vacuum.

.

 

Good luck

let us know if the actuator solves your problem.

Take care

Paul

 

My C43 was Honking like a goose. This is what was replaced. I don't think I had any boost issues just Honk Honk. Only 35k

 

You mean the pressure transducer? That is a common issue on these engines but at least it is not difficult and not expensive to replace.

 

The new solenoid did not solve my problem. At this point, everything I have checked seems to be good. I'm worried I need a new pair of turbochargers to get wastegate flaps that line up right...

• No boost leaks at any charge pipes
• Wastegate actuators fully actuate and hold vacuum at 17"
• Vacuum pump check valve replaced, holds 28" of vacuum at idle
• Boost control solenoid replaced (new one had same behavior as old one, so if someone can outline a better diag for that, maybe the new pierburg part was bad)
• Wastegates do not actuate in and out at idle
• No vacuum leaks between check valve and solenoid or solenoid and wastegates

Is there anything else I can diagnose without spending money? At this point I have a diag appointment scheduled for Wednesday at my local dealer in the hopes to find out definitively what's wrong and I pray it's something trivial that I'm missing and not needing a new pair of turbochargers, because that's expensive and will no doubt snowball into a pair of modalworks hybrids

 

Ok a few things:
1.your Autel scanner might not be able to read all the codes including some hidden ones especially if it is a lower end model scanner
2. maybe your vacuum tester was faulty
3. So based on the above it might still be possible the car is still in some sort of limp mode unless you can rev to redline no problem?

Guess you have no option but wait for the diagnostics.

 

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 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.