Persistent boost problem here - Mercedes-Benz Forum
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post #1 of 4 (permalink) Old 04-22-2019, 02:37 PM Thread Starter
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Date registered: Apr 2019
Vehicle: 2007 W164 (320CDI 4Tech)
Location: Fl Keys
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Persistent boost problem here

OK ladies and gents.

So, I bought my car (07 CDI) and as soon as I left the dealership (no warranty, of course, since it has 101,000 it immediately gave me a P0299 code. Turbo underpressure. It immediately went into limp mode.

I take it back to the dealership, and they reset the code.

I get it home, and it doesn't happen again. I drove it hard, lots of boosting, and it drove fine for a few days, and then it starts boosting under heavy acceleration, and then it cuts out. It's like it wants to boost, but then it doesn't. it does not go into limp mode, though.

I take the engine plastic cover off, and take the turbo T-duct (from turbo to intakes, or vice-versa ) and I notice that the duct's ends are cracked, frayed, broken off and barely holding on. So, I order a replacement thinking that's where the air is leaking from. I wait patiently to receive the brand new OEM part, and installed it.

It is doing much better, but it's still chugging hard under lots of boost. It goes past 3k RPM, and then it's like it cuts out or something.

Does anyone have a similar problem? Using the search feature on this site (and on Google) it tells me lots of options, but the most common one is that electronic wastegate controller can be the culprit. I checked all the wiring to make sure they're all connected. It looks good, but am I missing something?

Any help would be appreciated...

Thanks all
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post #2 of 4 (permalink) Old 05-21-2019, 02:59 PM Thread Starter
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Welp, after posting and gettin no replies, I'll try to let you guys know what the problem was, in case someone has the same issue (in the future).

About a few weeks ago, I took things apart to see what was wrong. At first, I found that the intake shroud (T duct going from the turbo to each intake) was cracked in multiple places, and barely held together. This thing also houses the MAF. So, I ordered one (375$). I didn't know if that was the problem or not, but I knew it was wrong, since it shouldn't be cracked and broken.

I installed it and the problem was better, but still there.

I then researched more, and found that the Sprinter van has constant problems with that turbo wastegate actuator. Technically, Mercedes doesn't want you to buy just the actuator, they want it to be a part of the turbo itself. Forcing you to buy the turbo and the actuator as one. I found a few new ones (not Bosch, but still direct replacement) and decided to spend the money and see if it works.

Guess what, it sure did work. I beat that thing up many many times, and it works great. I put it through a lot, trying to see if it would give me a code, or chug, or anything.. NOPE, works as it should!!!

So, Turbo-Wastegate Actuator is a common known problem. And you can buy one for 110$, and change it in 30-45 minutes.

This is the one I bought

I hope my struggle can help out someone in the future...
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post #3 of 4 (permalink) Old 05-21-2019, 04:24 PM
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There are 2 types of limp mode, one that limits engine rev to 3k max (soft limp) & other locks transmission into 2nd gear or reverse only (hard limp). The VGT positioner can cause soft limp w/o showing a CEL in IC & often reset next drive cycle to give false belief nothing wrong. There will be a stored DTC though so must scan for them to verify whenever acceleration seems sluggish & engine won't rev past 3k in N. I just bought one of those T-ducts w/ MAFs from FCP Euro on Fri & was amazed to find it sitting by my door on Sunday! I'm hoping it will increase MPGs as opening of original has largely disentigrated & pieces of it are floating around in valley of engine. Previous owner let a piece of that plastic around seal get into impeller so while positioner was causing limp mode, turbo was all chewed up too so replaced w/ new.

Last edited by PSDCamperVan; 05-21-2019 at 04:30 PM.
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post #4 of 4 (permalink) Old 05-22-2019, 07:31 AM Thread Starter
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Yeah. The first time, it went into limp mode where it wouldn't go up in RPMs. You can eventually go on the highway at speeds, but it wasn't going to get there quickly. It gave a code, as well. But, I could reset that code and it would drive fine for a few days, and sometimes not even throw a code again, or go into limp-mode. It just would chug.

That duct (I also bought from FCP) was OEM (or OEM quality, I can't tell the difference, it's that good). However, it didn't fix it. I'm sure it made it a lot better, not having compressed air escaping. But, it isn't the problem.

The Wastegate actuator has a known problem of the solder separating, and it wouldn't give you the right PSI at the right moment. That would cause the engine to chug. So, a quick replacement and the car rides amazing now. I'm impressed of how good this thing pulls...

If you change that duct, and still have the problem, make the wastegate actuator your next move. It's 1/3 of the price of the duct, and it'll fix the problem.
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