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If they tested the wastegate actuator and found that one is leaking that is likely the cause of the low boost. The boost air from both banks converge at the intercooler on the M276 and if the left turbo is low on boost, the right turbo will be working "double shift". The backpressure difference on both engine banks could be the cause of some rough running, however, not sure if it could be sufficient to affect the tranny smooth operation as you are reporting. Unfortunately, the wastegate actuator is a part of the turbocharger assembly so you won't get a separate PN from MB. An specialized turbo shop might be able to replace just the leaking wastegate actuator.
Last edited by Andre Cateb; 01-17-2024 at 11:50 AM.
OK, how does the waste gate "leak down" since it is a simple mechanical door controlled by the actuator. My understanding is that our waste gates are normally OPEN to avoid a failure in the vacuum line causing engine destruction. With NO VACUUM, the waste gate will be open and is only closed on command as long as there is adequate vacuum and the controller signals the actuator to close. Unless the waste gate flap has broken off, it's not a wear part that should "leak". Otherwise, you would have NO boost from the left turbo.
While the waste gate may not be separately available from Mercedes, I would be interested to see if the manufacturer (Garrett?) offers it separately. Also, you may want to contact Weistec since they modify and rebuild our turbos (at least for the M276.8XX engines).
Were you thinking of doing the work yourself with a used turbo? If so, I would definitely try to find a replacement part first.
You are correct that the wastegate itself is a fail-open valve, however, the wastegate actuator has an internal diaphragm and a spring. When pressure is applied to one side of the diaphragm it actuates to modulate the boost pressure. If the diaphragm is leaking (which is what I understood the shop diagnosed) the turbocharger pressure is likely fluctuating a lot or not modulating correctly.
Edit: I believe original turbos on M276 TT are IHI.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Well, if the technician meant the actuator, that's not what was written down. In my VW/Audi days, I did have the waste gate door/flap break off an aftermarket turbo, so that is what I thought the technician was referring to by waste gate. WRT AliExpress, $30 or $40 for both is worth the risk versus $4000.
And, I think IHI is the correct brand for the M276.
Please get a second opinion from another good workshop.
Your 2015 GL450 engine is the same as mine, a V6 3.0 Turbo, but with higher horsepower than my E400 I believe. M276.820 is mine.
The explanation by the workshop, I do not accept.
Wastegate flap, the coin shape, is not tested using VACUUM. No way.
The vacuum actuator for pulling shut the wastegate flap/coin yes....using vacuum to test.
Also during any test, manually the wastegate flap need to be pulled hard enough to close, or else false leak will occur.
Yes, our M276 wastegate is NORMALLY OPEN, the vacuum actuator is. The wastegate flap itself if not supported by anything is like a loose house "window." in the wind.
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First verify that the Y101/1 bypass valve ( aka DIVERTER VALVE ) a COLD side of the turbo is not torn. We will loose boost when it is torn.
Testing wastegate if turbo is still on engine usually smoke test is used at and some pressure. Below are the "holes" to plug :
01. Remove throttle body. 02. Remove aftercooler.. 03. Plug the intake manifold with those smoke kit "baloon".
04. Disconnect the duo check-valve of PVC and Fuel vapor injector. 05. Plug-off end of plastic hose item 5. 06. Plug-off end of stiff plastic pipe of item 6.
05 and 06 must be plugged or else pressure escape the engine via the PCV system.
.
07. Remove both CAT & 1st muffler, can't remove only 1 side if for M276 Turbo.
. 08. Plug the turbocharger Turbine blade hole ONLY.... with smoke kit balloon. The wastegate is there, at hot side of the turbo.
Before doing 08, send a boroscope to inspect the wastegate. Check for crack or excessive play.
What do I mean by 08. Plug the turbocharger turbine blade hole ONLY.... with smoke kit balloon ?
Why only the turbine blade hole ? Assuming one can do it
Wastegate hole and turbine blade hole shares the same exhaust gas flow.
So when you are able to block the turbine blade hole only, the smoke test with say 3 PSI of pressure will then have to force its way thru a "leaking" wastegate flap and
there you can see if it is indeed leaking.
Best to ask a turbo expert. I am not a turbocharger expert. I only know how our M276.8 is rigged. So if it were me, and turbo still on engine, 01 to 08 is what I would do.
I bet, 99% a turbo expert will tell you to remove the turbocharger and a proper inspection on the wastegate and turbocharger would be done on the bench.
Super small crack is common on turbo. See Master Tasos channel.
Agreed... I'm assuming they meant the actuators because, as pointed out by you and S-Prihadi, I also don't believe they would be able to measure the leak of the actual wastegate valve in a fully assembled turbocharger.
I don't have a place and time to play with these, however I understand how to check some of those things.
On the internet I found the actuator only or I can also get the whole Turbo piece (used obviously) and get that part only to be replaced if that will help. If I only knew it is a culprit.
I don't have a place and time to play with these, however I understand how to check some of those things.
We understand not everyone has the space, time, and knowledge to repair these cars, but if you are willing to invest some time you can have peace of mind in the long term. Recall your engine has another turbo waiting for maintenance, and even if you decide to replace it with a new turbo, or get rid of your car, the next one will likely have one.
Members of this forum will help you sort out your issue to the best of our abilities.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
@S-Prihadi recommendation is totally thorough. But, I personally would put a hand vacuum (or other vacuum device) on the actuator, pump it until the wastegate closes, and watch to see if the actuator rod moves (because of a leak). Leave the engine OFF when you are doing this. Doublecheck with the other side just to make sure I'm not full of it. It it moves, then there is a leak somewhere. If the suspect one moves and the other one doesn't, then it's the actuator assembly. For $4000 I would certainly try to replace it first.
NOTE: The pictures below of the engine and turbo are for the M276 bi-turbo engine and are intended to show the location of the actuator vacuum connection, not the exact part for all engines.
MityVac or other suitable vacuum pump.
Disconnect vacuum line here.
Attach hose from hand pump here.
for the actuator https://www.ebay.com/itm/404256472764?hash=item5e1f903ebc:g:plMAAOSwWVlkQ4cO&amdata=enc%3AAQAIAAABAHeURjr1nWKg2YQd1uEZ3WCZ5QRhadUaF30H9uQk5hjYtLSHDMZvdexUYsAuD9IB50GBV%2FKczsLWHfhPITYrK7OS8mvc4HioII5pRecklbacrqiCXJSV0xTioYdJAmhP5huaMbLqDL%2FYT5iWhySEOsFWwI4SWxbT%2B9IBEumPFcoOkdsK3t9r2nZ2CTUq4U%2BaQjCSqrRXlHgph4RER2sH4CtJ38pHtue7iI6y9fjvi9AdB2MNcr1FLDDRwY%2FFGKEE7xvVge7XiBeiWvF1E3FusmZLqPpX2gITWSIRfUy9kQjLdOgo1WcSw7oT99pUQISQFX8rYs8s8%2FZhlkq%2Fq67eDtc%3D%7Ctkp%3ABk9SR9qkjaqjYw and it looks like people were having the same code P02990.
My actuators have curved rod. I checked both today visually and the way they work is the same, they shake/move a bit forward and backward. But since the diagnostics shows the issue with only one of them, there's a dilemma:
Shall I get the actuator like the one from the link? Or
Shall I pay attention to the boost controller solenoid? O
My actuators have curved rod. I checked both today visually and the way they work is the same, they shake/move a bit forward and backward. But since the diagnostics shows the issue with only one of them, there's a dilemma:
Shall I get the actuator like the one from the link?
I appreciate your help and advices. I may do the test later as it is very cold outside.
Read amazon reviews for the actuator like this and it looks like people were having the same code P02990.
My actuators have curved rod. I checked both today visually and the way they work is the same, they shake/move a bit forward and backward. But since the diagnostics shows the issue with only one of them, there's a dilemma:
Shall I get the actuator like the one from the link? Or
Shall I pay attention to the boost controller solenoid? O
both ?
I would first test the actuators for leaks. If neither is leaking, check the pneumatic lines that connect the actuators to the boost controller solenoid. In my experience, when the boost controller fails the reduction in engine power is very much perceptible.
On my engine (M276.820) the actuator on the right bank has a rod with a curve while the left one is straight. Before replacing, I would recommend measuring the pressure (on the good side) at which the rod starts to move and the pressure it reaches the end stop so you can adjust the new actuator to the same values. You adjust that by changing the positions of the nuts in the threaded side of the rod increasing or decreasing its length.
Good point. Since the other one is working without throwing any codes, I definitely need to check the pressure on the good one and then compare with the "bad" one. It's still winter in MI, so need to wait a bit to get warmer outside unless I find someone with a garage to perform the test.
Also as I understand the rod should not be moving forward and backward. It must be steady on idle,
Correct, good actuators should be very much on their full actuated position (wastegate fully closed) with the engine at idle. If they are moving back and forward it's a good indication that you have a pressure leak somewhere in the system. It could be on the actuators diaphragm or in any of the lines themselves. I'm assuming (since there is only one solenoid valve for both wastegate actuators) that the pneumatic lines from both banks are interconnected somewhere, hence a leak in one side would affect the other one as well.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I think at idle the waste gates are open, so as not to build boost when not needed. Or, at least that is my understanding. However, because our turbos use a separate vacuum pump and not engine vacuum, I don't really know. I just know that they are open by default. I guess you could watch the rod and see if it moves when the engine is turned off.
Red: Ideally the wastegates are closed at idle, but the ECU can do whatever it wants. There is/was an issue with some where the ecu was letting them sit kinda in limbo and floppin around for no reason. They still open/close waaay too much, this was simply making it worse. The end result is people end up with worn hinges and they're screwed. One of the tweaks on my car is holding the wastegates closed more firmly, and for longer, so they only move a fraction as much and less often.
It seems obvious this mechanic was describing (poorly) a vacuum leak. Or perhaps just or lack of vacuum? Since I do not trust mechanics at all, I'd check that out myself. I'm sure plenty of turbos have been replaced when it was just bad vacuum line. Low vacuum will also cause the same low boost. Not sure how or where your check valve is but mine is on the vacuum pump and is basically guaranteed to fail, and low boost is the result.
If the diaphragm really is leaking, it's easy to check as others described. If it is, I'd find a used one, or patch yours. Or get new ones. Just because MB doesn't sell it doesn't mean the mfg doesn't. Nor does it mean you can't replace with similar.
If you really wanted you could replace it with a spring and to hell with the diaphragm.
Also, my car was saying turbo #1 low boost, but it cannot tell between the two so there is only low boost and you ignore the #. And closing the wategates at idle is a hella lot easier than under load, so if closes at idle it doesn't mean much. If you can make 7psi then it can clearly close them at idle and appear to be fine. And if one side leaks, the other shares it, so they'd both actuate at the same time either way, and make low boost together.
Lastly, when mine had low boost, about 7psi at peak, it was not mechanical. It was the frikkin ECU! I never figured out why, or how to fix it. Instead, I tuned it to make more and more boost until I got it back. Fyi in case there are no vac leaks.
That's very interesting point there.
Since I'm not a mechanic, could you advise how to check the leak (vacuum line) and where? (If it's the way to connect the vacuum pump to the actuator, then I know what to do; if there are other methods, I'd be happy to consider). Since it's a waste gate issue, can I play with the screws on that rod? Say, making it longer/shorter could keep the flap more steady. Or is this mechanism worn from the inside and you cannot regulate it just like that?
And if one side leaks, the other shares it, so they'd both actuate at the same time either way, and make low boost together.
At least I got an answer why two of the actuators move forward and backward.
Hope the ECU has nothing to do with it but I can tell after I perform all the aforementioned operations.
just find the vac line(s) between the turbos and solenoid. it should T off to two lines, one for each turbo. you can use a tool to draw a vac on the pair, or each, or just suck on it like i do (standing by for jokes). id check the line feeding the solenoid as well. check for oil in the line too, which tells u the check valve at the pump is fubar. at least on mine it does.
My actuators have curved rod. I checked both today visually and the way they work is the same, they shake/move a bit forward and backward. But since the diagnostics shows the issue with only one of them, there's a dilemma:
Shall I get the actuator like the one from the link? Or
Shall I pay attention to the boost controller solenoid? O
both ?
Today was warmer weather and I checked both of them again.
UPD. The driver's side actuator is not curved, but has straight rod (last time I checked it was dark outside). And after I start the car they are being pulled, like on the video above; I'm assuming they are working correctly. They both have a slight backlash when car is idling, I'm also assuming the vacuum is good; however clumsy coin flap at waste gate is the result of 9 years vibration, it could just worn out.
Still waiting for the weather to get warmer.
Does anybody know if it helps a bit if I play with the nut on that rod (making the rod "smaller/longer")?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Ancore
Today was warmer weather and I checked both of them again.
UPD. The driver's side actuator is not curved, but has straight rod (last time I checked it was dark outside). And after I start the car they are being pulled, like on the video above; I'm assuming they are working correctly. They both have a slight backlash when car is idling, I'm also assuming the vacuum is good; however clumsy coin flap at waste gate is the result of 9 years vibration, it could just worn out.
Still waiting for the weather to get warmer.
Does anybody know if it helps a bit if I play with the nut on that rod (making the rod "smaller/longer")?
Approach this systematically, eliminating possible problems. See post #35 above to check if the diaphragm on the wastegate actuator is good by seeing how long it holds vacuum. If both are good, move to the next component. I would NOT futz with the nuts or tension on the waste gate actuator until you get this problem resolved. You are only treating a symptom and not a cause. And, likely it will cause limp mode once you figure out the real problem and fix it.
At idle, my wastegate actuator rods are rock steady. They do not move at all (nor should they).
What Andre said. The rods are adjusted so the two turboz match/make the same boost. You can adjust them, but I wouldnt until you find the issue. If you cant fix it, you could adjust as a bandaid fix.
If you get a cheap OBD dongle and Torque Pro app, you could check the turbo duty cycle. If theres a leak the the dc will up at 90 or 95 trying to compensate. Otherwise it will be less, which means it has enough vacuum and is bleeding some off. So 90 or whatever is it trying to give the turbos as much vac as possible because itz not getting enough boost. less than 90 is saying i have enough vac and am making my boost, or too much boost, and itz lowering vac. so a dc of 10 would be zero boost. the dc varies eng to eng, but mine was a min of 10 n max of 90. if any of that makes sense.
01-17-2024, 11:11 AM
