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Probably applies to all gasoline turbo version of MB.
Anyway, I want to share some findings.
In M287 it is called Y77/1, Boost Pressure Actuator
In M276 3.0 TT (M276.8) it is called Y31/5, Boost pressure control pressure transducer
In my Xentry 2020 TESTS menu, it is called Y77/1 Boost Pressure Positioner
What does it actually do ?
Starts at 5:30 minute, but its working is based on vacuum pump ( suction ) of our engine and not positive boost from turbo compressor or intake manifold of a turbo engine.
If it is on its way to "die", it will not close the wastegate internal flap properly (via the vacuum actuator unit ) and our engine proper turbo boost will not occur. CEL may not appear, till real under boost is detected.
Why am I discussing this ?
Because you can detect its aging using Xentry, before it cause boost loss. Dang, I wished I did this test while in Jakarta and not while in Bali ...
At 45% duty, it is only a tiny bit less pull compared to 90% ( FULL PULL ) or 10% ( NO PULL ). "Pull" as in the vacuum actuator pulling the wastegate to close shut.
Mine now if I mess ( unplug and plug ) with the vacuum hose, the solenoid can flutter, like a bad mini trumpet ...ha ha ha.
My turbo boost still okey, 11.2 psi from maximum of 11.9psi ( 0.8 BAR ).
Why am I intrigued by this Piesburg solenoid ?
I am curious as to how the ECM/ECU can detect the solenoid duty cycle at 45% ?, when the connection is a mere 2 wire and there is no position sensor on this solenoid.
I don't have proper tools to troubleshoot it now in Bali, got to wait till I come back to Jakarta .....to mess with how/where the 45% come from.
The fun part is understanding how the ECM/ECU get that 45%.
I hope either the new one arrived in time from MB Indonesia before I drive back to Jakarta 1,300plus Kilometers or if no new one in time,
it will stay nice and don't burnt out on the way home. Limp Mode maybe executed by the ECM if no boost and then I forced engine to run hard.
I attached information from Piesburg ( general ), which has good info. Mine is within 12 ohms coil resistance but I can't confirm the document is 100% accurate to
my version of the solenoid.
If this solenoid duty is a mere OPEN or CLOSE or full pull or zero pull state, it is easy...but PWM pulse from ECM as fine control means it is more
advance and can do variable turbo boost pressure as per engine mapping which depends on temperature , load, altitude and yada yada.
I also attached a Texas Instrument document on how a shunt design ( basically a current sensor ) at page 5 can explain on how the ECM/ECU estimate that 45% duty cycle without
having to use position sensor.
As a bonus, attached a study by someone on a Piesburg solenoid.
I would like to add.
Since the design for this boost controller is FAIL SAFE in relation to the turbo charger boost, if this Piesburg solenoid fails, the spring inside the vacuum actuator will push open the wastegate,
as no vacuum is pulling it back.
Me never really study our engine turbo boost control strategy, till now
So when our vacuum pump at Bank 2 (left bank) is say severely leaking.... not only we loose easy boosted braking, we will loose turbo boost too.
The so called DUTY CYCLE/ACTUAL VALUE it is showing............. is what the ECU pumps out to the solenoid.
So it is NOT a measure of the solenoid actual PERFORMING DUTY CYLE mechanically.
Why the hell did the Xentry showed as RED !!!! and give 70%-90% as specified ??!!??
I scoped the two wires feeding the solenoid and I saw the 40% duty cyle.
It uses 300HZ frequency. I think that is what I saw. I shall update the Hz value when I test more yah.
Sorry I did not screen capture the scope readings. It is a 2 channel Pico Scope 2205.
90% duty cycle is possible to do with TEST mode in Xentry or in my Autel.
Anyhow, the new solenoid is smooth and no funny fluttering noise when I closed/block and un-block the small* hose outlet barb at the solenoid ( *this goes to the turbos ) with my finger.
So I am happy with the new solenoid ( no test drive yet ).
I am pissed though with Xentry.
Autel does not show SPECIFIED value, so no warning or red text at 40% duty.
Here is the the boost controller working in real time, its duty cycle, frequency, vacuum value to vacuum actuator and vacuum actuator mechanical pull distance.
40% duty cycle and approx 9 incHg Vac. As to how much in PSI resistance value the wastegate is closing shut.... I don't know.
Since exhaust system is an open ended one and factory spec, I doubt back pressure would be high.
90% or MAX duty cycle produces 25 incHg Vac.
If one can and know how to calculate the size of the vacuum actuator, its built-in resistive spring and dimension of the wastegate flap itself,
I think he/she can figure out : to how much turbo boost in PSI this vacuum actuator can actually handle.
One thing for sure, the vacuum flap is good to minimum 12 psi ( 0.8 BAR ) of turbo boost this M276.820 has, or 13 psi ( 0.9 BAR ) of the M278
My old one was doing that, and the new one is not. Not swapping this part will accelerate the wastegates wear since, they are opening, and closing constantly when they are not supposed to.
Thanks for the video and analysis on the control system and the wastegate flappers. So when waste gate flapper goes bad, it's the rod attached to the flapper that wears the bushing it rides in. this lets the flapper move off axis , not close properly and this wont allow boost to build.
Are you saying the root cause for this may be the vacuum boost solenoid not working well and then the rapid cycling of the WG flapper causes wear on the shaft /bushing over time?
Thanks for the video and analysis on the control system and the wastegate flappers. So when waste gate flapper goes bad, it's the rod attached to the flapper that wears the bushing it rides in. this lets the flapper move off axis , not close properly and this wont allow boost to build.
Are you saying the root cause for this may be the vacuum boost solenoid not working well and then the rapid cycling of the WG flapper causes wear on the shaft /bushing over time?
I just bought a 16 gl450 m276 and I noticed i have the same issue shown in this video. The wastegate flaps on both turbos are loose. Besides replacing the boost controller, I would also have to replace the turbos to fix the worn bushings as described in this thread? Or could the wastegate flaps be replaced with new bushings? Any help would be greatly appreciated. I am used to working mainly on Audi's and this is my first benz. Thank you!
Cheers!
Only when u loose boost, then u start to worry about the wastegate* itself ( *among others ).
That "looseness" is standard as-is, when vacuum actuator is not pulling.
I never seen wastegate repair kit yet for our MB, but I seen Bimmer boys doing such repair.
Care must be taken due to super hot temperature these metals are exposed to, so the repair kit must be suitable for the metal expansion or otherwise when hot it may freeze/stuck, sort of
Only when u loose boost, then u start to worry about the wastegate* itself ( *among others ).
That "looseness" is standard as-is, when vacuum actuator is not pulling.
I never seen wastegate repair kit yet for our MB, but I seen Bimmer boys doing such repair.
Care must be taken due to super hot temperature these metals are exposed to, so the repair kit must be suitable for the metal expansion or otherwise when hot it may freeze/stuck, sort of
Thanks for your response. I am losing boost. No power. Sometimes when manual shifting I can gain some boost. I have a code that sets as soon as I drive once I clear with the scan tool, p0299. I was wondering if I can adjust the wastegate rod by tightening the adjustment nut. From your response and watching the youtube video posted on this thread, a set of turbos and a new boost controller will need to be done to resolve this issue, right?
Dont adjust the rod, never do that. Its length is calibrated for good working pull from vacuum actuator which this vacuum actuator relies onthe boost controller accurate opening of its valve to
get vacuum suction flowing.
If your vacuum actuator does that dance and is NOT LEAKING, first replace the boost controller , but do check if the vacuum lines to it from vacuum pump is healthy or not.
Ur engine is M276 3.0, there is also a diverter valve (bypass valve) which can leak and a check valve at the intake manifold which can leak too, read here : https://mbworld.org/forums/e-class-w...leak-path.html https://mbworld.org/forums/e-class-w...-0tt-m278.html
Check the easy ones first, and then if those are good, you look at your wastegate. How many miles is ur engine ?
Dont adjust the rod, never do that. Its length is calibrated for good working pull from vacuum actuator which this vacuum actuator relies onthe boost controller accurate opening of its valve to
get vacuum suction flowing.
If your vacuum actuator does that dance and is NOT LEAKING, first replace the boost controller , but do check if the vacuum lines to it from vacuum pump is healthy or not.
Ur engine is M276 3.0, there is also a diverter valve (bypass valve) which can leak and a check valve at the intake manifold which can leak too, read here : https://mbworld.org/forums/e-class-w...leak-path.html https://mbworld.org/forums/e-class-w...-0tt-m278.html
Check the easy ones first, and then if those are good, you look at your wastegate. How many miles is ur engine ?
The current mileage is 105k. With engine off, i can move the flapper by hand. Actuator seals are good. Vacuum to the wastegates are good.
You misunderstood my video, I did not have bad wastegate rods, I had a bad actuator (the plastic thing) above the engine.
You are going to bend the wastegate rods, and cause irreparable damage, which will turn into emotional damage.
Thanks for the warning. I figured I shouldn't do that. I have a biturbo audi and those wastegates can be adjusted for preload so I was wondering if the same concept can be done with the m276 motor. Guess not. So in the video I can see how the bushing gets worn out and has to be replaced. That just looks like too much work to do. Based on what you see in the short videos I shared, the flaps shouldn't have play and I would need to replace the turbos or the boost controller or both?
Thanks for the warning. I figured I shouldn't do that. I have a biturbo audi and those wastegates can be adjusted for preload so I was wondering if the same concept can be done with the m276 motor. Guess not. So in the video I can see how the bushing gets worn out and has to be replaced. That just looks like too much work to do. Based on what you see in the short videos I shared, the flaps shouldn't have play and I would need to replace the turbos or the boost controller or both?
Which video? Mine? if so, no, my bushings were fine. I swapped the $30 part, in 2 minutes, and I was done.
Which video? Mine? if so, no, my bushings were fine. I swapped the $30 part, in 2 minutes, and I was done.
It was the video @S-Prihadi shared in regards to the n54 turbo flap issue. I've never seen the wastegate flapper rattle. If I remove the wastegate I'm sure the flapper will be loose. I'm trying to figure out if the boost controller or the flapper is the root cause of my issue. I worked as a tech for 20 yrs until last year and started working in IT. I worked on a bunch of older model mercedes that were N/A engines. 1.8t, 2.7t, and 3.0t Audi's are my area of expertise. But in general, that video seems to make the most sense that the issue I have is the same and was ignored by the previous owner and now it's my problem lol. I guess I'm looking for a fix that doesn't involve pulling the turbos and spending 2k on a set. I appreciate all your feedback
Adari,
Our M276 turbo wastegate and its vacuum actuator is set as FAIL SAFE.
This means the vacuum actuator when engine is OFF or when it leaks and fail to pull, wastegate stay open and we loose boost so it is safe for the engine.
If your wiggle test on the stem of the wastegate shaft to actuator rod/shaft is during engine OFF, surely rattle will happen as that is the wastegate in OPEN state or "loose".
A little looseness is a must, as there is no bearing other than bushing allowing the wastegate shaft to spin 90 degrees between open/close.
In S-M case, his boost controller (the black plastic electrical solenoid) is the bad dude. The amount of duty cycle sent out to that boost controller could not be mechanically delivered well enough and
the vacuum actuator never pull properly and boost leak occured. Only in a 100% pull state of the vacuum actuator and able to overcome 11psi of max boost and mechanical link friction/losses,
the wastegate coin shaped seal/gate can then close properly. Assuming wastegate and its shaft is good.
Adari,
Our M276 turbo wastegate and its vacuum actuator is set as FAIL SAFE.
This means the vacuum actuator when engine is OFF or when it leaks and fail to pull, wastegate stay open and we loose boost so it is safe for the engine.
If your wiggle test on the stem of the wastegate shaft to actuator rod/shaft is during engine OFF, surely rattle will happen as that is the wastegate in OPEN state or "loose".
A little looseness is a must, as there is no bearing other than bushing allowing the wastegate shaft to spin 90 degrees between open/close.
In S-M case, his boost controller (the black plastic electrical solenoid) is the bad dude. The amount of duty cycle sent out to that boost controller could not be mechanically delivered well enough and
the vacuum actuator never pull properly and boost leak occured. Only in a 100% pull state of the vacuum actuator and able to overcome 11psi of max boost and mechanical link friction/losses,
the wastegate coin shaped seal/gate can then close properly. Assuming wastegate and its shaft is good.
Thank you for providing clarity on this. The wastegate rod and wastegate itself is good. I did notice a difference in readings when looking at the inlet manifold pressure. I am picking up a new controller or as MB dealers call it the pressure transducer for $80 today. I may just grab a new manifold sensor as well while I'm there. I'll update with some good news hopefully later today. Thank you all for helping me. I will consider a turbo replacement in the near future before tuning. I want to make sure mechanically everything is running properly and no more codes before taking that next step. Can't wait to feel what power this engine has. My Q7 had a stg2 tune and was dyno'd pushing 415hp/345 ft lbs torque so I miss that.
Update: Replaced boost controller, cleared code p0299 and issue still not fixed. As soon as I start driving, the code is set. Checked vacuum hoses and I can't find any leaks. The only thing I can think of is the pressure sensor that is not reading correctly. Maybe I can swap the inlet with one of the other 2 pressure sensors and see if I get a negative reading. Any other thoughts?
Adari,
What scanner are u using ? The 0299 Boost Pressure is too low DTC is not from Xentry if your engine is M276 3.0 Turbo with MED177V6LA engine computer.
Nevertheless here is how boost is actually measured by my engine computer :
#1 Pressure sensor before the throttle body and the #2 Manifold Absolute Pressure at the intake manifold which is after the throttle body.
So, it is not a single sensor job.
The 2 pressure sensors at the air filter housing also play a part, but not about turbo boost.
NOTE : Ambient pressure is a calcualted pressure using special strategy.
Boost pressure based on 2nd Xentry image is the one at the aftercooler, not the one at the intake manifold.....but....
You can't swap those two around, as they are part of the overall BOOST calculation, I am sure because they work at the boosted air region.
What separate them a part is one is after and one is before throttle body, so another X factor the engine computer need to calculate depending on throttle opening angle
Are the wastegates shaking? How much boost are you making?
Thank you
Wastegate flaps no longer rattle at idle after installing a new boost controller. If I manually shift through the gears, there seems to be more power and somewhat builds boost. I'm still in limp mode because of the code setting everytime I erase and start to drive.
10-30-2021, 03:00 AM
