edwardscpa

Did a second test drive of an S65 today and after being driven gently for a few miles, while rounding a gentle curve on a highway I changed the drive mode from C to S and changed the ABC mode to S as well. When I went to accelerate, the car had no power. Like the throttle body would only open but so far. Engine ran smooth and idled smoothly. The transmission seemed to work ok, cycling through the gears based on speed, and you floored the pedal, it would hold a gear up to at least 3000rpm, but there wasn't enough gas flowing to make it take off.

The car had 1/4 tank of gas and it was hot and humid outside.. Like 90*. The engine temp was above 80... About halfway to the next tick mark. The AMG gauge read 214 degrees F. No CEL. Didn't try restarting it.

3 owners in 38k miles. Carfax had a clean service record with nothing significant, but 400 miles before it was last traded in, it noted the ECU and similar items were diagnosed.

What might the problem be? Should I run, or just have them fix something in particular and go with it? I'd have a warranty...

Welwynnick

Probably a failed IC pump or air in the IC system.

If it was serious, there would be a CEL.

But really, this is someone else's problem.

Nick

sloanbj

Manual for some models recommends not changing modes while under way.

edwardscpa

I recall seeing other posts mentioning that, but some thought that was akin to not operating the navi while driving warnings. ...and why wouldn't you be able to cycle into and out of sport or manual modes while driving? Or putting ABC into sport when you hit the freeway?

Surely people do this all the time... Is it known to cause this issue?

Dealer is presently working on the car trying to diagnose it...

EDIT: also, manual says "AMG vehicles: only change from automatic drive program C or S to manual drive program M when the vehicle is stationary." So changing b/n C and S is fine. But doesn't the button go C-S-M-C etc in a cycle? If you changed to S mode, how would you get back to C without passing through M?

edwardscpa

The dealer spent some time diagnosing the car and said it was an intermittent problem, but they say they narrowed it down to a turbo waste gate that sticks open once the engine heats up. Said the part to fix it costs $8k (new turbo I assume) and would take 15 hrs. I'm hoping to get the codes tomorrow. ....does this diagnosis even make sense? Don't see why you'd replace the whole turbo...

Said to IC pump was working.

Thoughts?

Welwynnick

I'm a bit confused. Is this your car or their car?

Sticking waste-gate? Does anyone else think this sounds like they're guessing?

Waste-gates are normally closed, and the compressed air line OPENS the waste-gate to relieve exhaust gasses. If the waste-gate was sticking (not inconceivable) then the engine would still be getting boost.

Indeed it would get too much boost under some but not all circumstances, and this would be detected by the ECU and TCU, which would throw codes and shut things down. If the waste-gate was at fault, I expect it would limit throttle opening.

That all seems a bit unlikely, but if it did happen, you would still get boost across a large range of engine speed and load conditions - just not near peak torque.

My feeling is your dealer needs to look harder. Suppose they changed the turbo and the fault was still there? What next?

Nick

MooksM275

Just wanted to add that on our cars its actually the other way around. Our wastegates are open by default. The boost pressure control valve pulls the wastegate shut. If the wastegate is not shutting then this will be a problem.

However, the problems to cause this are various. Bad vacuum lines, bad boost pressure control valve, bad wastgate control diaphram, etc.

The boost pressure control valve is not expensive so may be worth a try. 50 bucks

Welwynnick

The waste-gates themselves are not spring-loaded to be shut; its the spring inside the control cell that does that.

The diverter valves open off vacuum from the manifold, and the waste-gates open off pressure from the IC's, upstream of the throttle.

I opened the waste-gates on my car using compressed air.




Nick

edwardscpa

Nick - it's still their car, but it's on hold for me. If this proves to be something that can be readily resolved, and if an inspection doesn't reveal anything else particularly damning about the car, I'd be OK buying it with a warranty. On the other hand, if it's grossly expensive to repair, they may not be willing to sell it retail at all. But I like figuring things out, so here we are!

I've been studying the Maybach M285 engine found under the link below. See page 57. Very interesting, and I understand the M275 works basically the same way? (I'd love a copy of this manual specific to the M275...) If so, then what Nick is saying makes sense... the springs that indirectly hold the gate shut are pushed open by pressurized/charged air. In the absence of this pressure, the gates should close and you'd get the boost.

So, if the bladder was bad or the lines leaked, you'd lose the pressure and the gates would shut. If the gates are open and pressure is being supplied, then maybe the Charge pressure control vacuum transducer flipped out, or maybe if it takes direction from the PWM Control Module (which also controls the fuel pump) then maybe that or the fuel pressure sensor is bad?

...cause I swear, the car went from having tons of pull to seeming like the throttle was capped at 3%. It wasn't merely a lack of boost... fuel supply was cut. So if I'm hearing you correctly and there really was a problem with the gates or some component, the lack of power came by direction from the ECU; the turbos could have still been supplying boost.

https://drive.google.com/drive/folde...EhCdUFmYVlKZ3c

Welwynnick

If you really want to find out about the V12TT, read this:


http://wenku.baidu.com/view/d810de04...3d5bb75ab.html

edwardscpa

Got more details... It took the dealer's tech several drives to replicate the problem. It threw codes and CEL apparently. Don't know the codes. After much testing, he tried to manually actuate the waste gates, and the passenger side turbo gate wanted to hang up. The driver side gate seemed fine.

The dealer is debating repairing or wholesaling the car. Obviously, they want to make sure they fix it the first time. So, they are concerning that if they replace the gate, the turbo will turn out to be bad. ..and if they replace one whole turbo, the other could conk out. So they are debating replacing both or nothing.

I understand risk avoidance, but have to believe that if the car were privately owned, you'd follow a different course. How would you go about working on this if it was in your shop? I don't imagine turbos are outright replaced often, am I right?

sloanbj

Shocking that MB flagship motor can't make it to 40k miles without significant failure. I would not purchase this vehicle.

Welwynnick

If it is indeed a waste-gate failure, it would be the first I've heard of.

Nick

edwardscpa

Carbon build up maybe? Is that a thing on these cars?

Would you describe the gate as internal or external? ...would you replace the part or the whole turbo?

Welwynnick

The waste-gate itself is integral to the turbine housing, so that would probably need a new turbo.

The waste-gate actuator (which MB call a vacuum cell) is entirely removable. I don't why it couldn't be replaced, but I don't know what you would replace it with.

I rebuilt both turbos on my S600, and yes, they were choked with carbon. If the waste-gate was choked with carbon, you could disconnect the actuator and loosen any carbon or corrosion around the pivot.

Nick

MooksM275

Thanks for the diagram.

Correct me if I am wrong of course, but by putting compressed air to your wastgates you actually closed them not opened them. Just wanted to clarify how they work. If you look at a turbo that is off the car (I had mine off as well), the wastegates are by default open. Then, as you said, pressure from the IC pressurizes the wastegate and shuts it. Therefore, at idle the wastegate is open, and when you open the throttle and start to boost, the wastegates shut.

edwardscpa

Might carbon buildup be the most-likely/simplest solution? Are there any fuel additives or something like that that could help burn off the deposits over a few hard runs? ..or is that way too simple? What would be proper procedure for cleaning the turbine side of the turbo?

Found this article amusing... granted these are different engines with regard to DFI, but on the exhaust side it has me wondering whether this car was more likely to have been driven by a grandpa than worn out at the track?

http://jalopnik.com/this-is-what-hap...udi-1691976274

shardul

iTrader: (1)

Connect the car to DAS, there will be a lot of soft codes stored in the ECU that will have to be cleared out before you get full power again.

Welwynnick

You MIGHT be right, but I don't believe so. Part of the reason for copying the diagram was because you can see that the diverter valves run off vacuum taken from the inlet manifold (downstream of the throttle) while the waste-gates run off pressure air taken from the RHS intercooler (upstream of the throttle).

Before turbos were electronically modulated like this, the inlet manifold pressure was used to actuate the waste-gates directly. The more the inlet manifold pressure - the more the waste-gates were opened. I think the M275 engine works in the same sense, just with the additional control.

There's some text in the MB M275 Initial Training slides that describes how it all works, and I think its consistent with pressure to open.

If it worked the other way round (pressure to close) you would have to be sure to have positive pressure available, and if you drive gently, the engine might not generate any boost at all, so you would have no waste-gate control. I don't think Mercedes would do that.

Nick

Welwynnick

Here's a picture of the waste-gate. You can see the and of the actuator rod just to the left of the turbo. The pivot axis is clearly below both the actuator and the valve. Therefore, the valve opens when the actuator pushes with increasing air pressure.

Nick

MooksM275

I don't know what I was thinking. Your right, the wastegate is pushed open. Thanks for the info and pic.

I don't know if u saw my thread that I re coded the ecu and my power increased. Now I think it was a massive coincidence. My power went down again. After this thread, I used a air pump to pump waste gates and visually watch them actuate. I saw them move but passenger side was a little slower to return closed. So I shut it all down and closed car.

Started car today, power was same low power. Then I stopped car and restarted it went up again in power. Out of the blue.

My iat temps are same all the time. I have no misfires. I have checked engine top to bottom and can't figure this crap out.

When car is in low power state, if I remove map sensor on intercooler, disconnect electrical, not a huge difference in power. The map sensor is new from Mercedes and is second one I got from them.


So I don't know, maybe sticky wastgate like the op here. I am going to get car in the air and hand actuate wastagate to see if it is ****ting. Maybe remove downpipe and double check.

Weird

edwardscpa

When you say low power, do you mean super low power like limp home mode? Also, are your gates corroded or have carbon buildup? What do you think is causing them to catch?

Keep us posted...

MooksM275

I dont think it is limp mode because I have a DAS XENTRY and there are no faults in engine or transmission stored or current. (I assume limp mode would show up)

My power loss is hard to describe. If I go full throttle when it is in that state, it will have 2 seconds of lag (for example 30mph in 2nd gear m mode) then boost comes on strong and car accelerates "fairly well" not great.

When it is not in "low power mode" part throttle has tons of torque and power.

So far:
I checked exhaust backpressure and nothing is wrong here. Catalytics are good.
O2 sensors looked dirty, so wondering if a laggy O2 is causing this. Will buy 2 new O2's (the lambdas before the CAT), and post up here. I guess they are almost at reccomended interval 88k miles.
Tested fuel pressure and all checked out.
No stored misfire codes-no misfire detection during driving or otherwise.
Boost when in low power has big delay but when full throttle does finally come up to full boost (according to range provided by DAS Xentry.

I'm going to look at some electrical. SAM units? the Big fuse block for front electrical? Input voltage for MAP sensors?

Ill check back in with more data. But for now, I am on second day of full power and no issues. One thing is that when I completely reinitialize the ECU and erase all adaptions the car instantly drives better, smoother etc. This is what I did in the beginning that miraculously "fixed" the issue. Now, I know that this is not the complete solution but is somehow masking the problem for a little bit and then the system I assume reverts back because of some problem I have. Sensor or electrical or....

Maybe have dealer try to completely reinitialize the ECU and erase all mixture adaptions and throttle learning. see if it is similar to mine.

MooksM275

Ok So I have a pointer on something now. I now highly suspect my car is in limp mode.

I was out with DAS XENTRY hooked up. Stopped car, had key on, sat for 5 minutes while using XENRTY. Started car and car had low power.
Drove for around 5 miles to confirm. Then went to XENTRY and did initialization of ECU where it erases and resets all mixture data and throttle stop positions. Started car and power is back.

So it seems my ecu is going into limp mode. If I had a stuck wastegate as my issue I dont see how my fact patter would fit. Also remember that I reset these adaptions the first time I had my power come back.

Look at this I found.

http://sprinter-source.com/forum/showthread.php?t=7173

Guy states that ECU and TCU have limp modes. It seems sprinters have this issue a lot.
More to come.....It looks like its some intermittent issue that is tripping the ECU to limp mode. Then resetting adaptions puts it back. I will report back if I can get it to do it again and am able to reset it like this.

I am now going to replace Crankshaft Position Sensor and Camshaft positions sensors. I will also monitor the ambient barometric pressure reading. I read that Sprinter guys have this sensor in the ECU and when it goes bad it causes Limp Mode. Obviously the computer uses the outside barometric pressure as a reference for the pressure readings inside the engine.

tusabes

Very helpful link at the bottom