OM642 VNT Turbo actuator issues - PeachParts Mercedes-Benz Forum

jay_bob · #1 02-02-2020, 03:20 PM

So the latest fun with the 2008 E320 BT, the next chapter in the saga that never ends...

Last weekend I was driving it around town for a shakedown before hopefully going to swap it back to my son and get my car back. Well not so much.

Going through a left turn I got a weird hesitation. It did it a couple more times when accelerating at low speeds, and couldn't quite put my finger on it.

So last Sunday night I put the Xentry on it and sure enough it was coming up with a fault.

2592-001
Check component Charge pressure positioner. Positioner signals fault. Current and stored

Drilling down into the fault description it takes you to a guided test. The 'charge pressure positioner' is the actuator on the turbocharger for the variable vanes.

The actuator lever on the turbo is supposed to move up and down to open and close the vanes inside the turbo. Well it was only moving a fraction of an inch and the actuator motor was whining and clicking loudly.

So I took the e-clip off the linkage and tried to move the turbo linkage up and down and sure enough it was frozen. So then I turned the key back on and the positioner moved through its range freely once it had been freed from the stuck turbo linkage and it didn't whine and click anymore.

Ok time to pull things apart and see what's up with the turbo. Found a couple videos on youtube showing how to remove the exhaust side housing and expose the sooty side of the turbo, without disturbing the sensitive parts in the center section.

Pulling the turbo is not crazy difficult but is a bit awkward. Done it before on the ML320 (oil cooler seals) and it is easier on the sedan than the ML. Until I got to the flange bolts between the right side exhaust manifold and the turbo collector manifold.

The bolts that make up these joints are single use, stretch to yield bolts. Unfortunately the shop that did the oil cooler seal job before I got the car did not heed this, and they reused the bolts (or used new bolts but did not torque them properly). Well one of them snapped off while trying to break torque.

Short list of steps to pull the turbo:

Intake side:
Intake Y-pipe
Charge air tube from turbo outlet towards intercooler

Exhaust side:
There is a short pipe section between the turbo outlet elbow and the DPF. This pipe is held by band clamps at both ends and a bolt on a bracket at the right rear corner of the engine.
This section of pipe needs to move out of the way to be able to get the turbo out. For now just get it loose.
Turbo outlet 90 degree elbow, 2 bolts on top, 1 below, (the one on the bottom does not need to be completely removed).
EGR 90 degree connector, 4 bolts, 2 pointing down, 2 pointing back into the EGR housing.
Exhaust manifold connectors, 1 on each side, 3 bolts each (this is one of the bolts that snapped)
Two bolts holding a bracket to the top of the intake manifolds, hidden below and behind the turbo. Do not break the connection between the turbo itself and the exhaust plenum as it is difficult to get this realigned on reassembly.
Two T45 screws at the base of the turbo center section.
One E10 holding a bracket to the front of the turbo.
Unplug the actuator.
Lift turbo straight up.

Once you have the turbo out then you want to remove the 6 hex bolts around the perimeter of the exhaust side. Very gently tap the housing to get it off the center section.

Once you are inside you will see the VNT vanes. I started wiggling the actuator arm and saw that the vanes were trying to move but were stuck with powdery carbon deposits. I was able to flush the VNT vanes out with brake clean and got everything moving nice and smooth again. Note that this is a dry assembly, it is intended to be run without lube. Any lube placed on the vanes will either decompose in the high temperatures or attract soot.

The turbo impellers had zero damage, spins nice and smooth, and no play to speak of. Remember the turbo spins on an oil film so there will be the tiniest amount of slop in the shaft at rest.

The turbo housing goes back on the center section easily. Watch out for the locator pin on the center section that aligns with a notch in the exhaust housing.

So while waiting for all the one-use gaskets and bolts to arrive I started trying to attack the broken bolt in the exhaust manifold. Tried to drill out the broken bolt but could not get a good bite with a drill bit to get an extractor on it. After a couple hours of fighting I went and found a manifold on eBay and it will be here Thursday.

It is actually quite easy to remove the exhaust manifold, they used the copper plated steel nuts and they were very easy to access and remove. First the heat shield comes off, 2 bolts up front and 3 at the back, then 3 copper nuts on top, 3 copper nuts on the bottom.

jay_bob · #2 02-09-2020, 12:08 PM

Finally got everything back together this weekend.

Car doing much better now.

I didn't realize how much it was down on power until getting this fixed. It never threw limp mode but it was getting slower and slower. And it would downshift abruptly when cold (like when coming up to a stop sign).

Hopefully all good for now, as soon as I get the sunroof recall fixed (waiting on the letter) then I can swap cars back.

TimFreeh · #3 02-10-2020, 03:14 PM

I've always kind of wondered how in the world a mechanical linkage that is supposed to adjust the pitch of the blades in a turbocharger could possible live for more than about 5 minutes in the environment where its constantly getting pummeled with high-velocity exhaust gas. I'm amazed this is the first time I've ever heard of issues with the associated linkage.

There was nothing broken I guess? What are you impressions about the long-term durability of this kind of setup?

I've got lots of OM648 CDI experience but I've never had to mess with any turbocharger issues, I was aware the OM642 had the variable pitch blade setup - do you know if the OM648 has the same setup?

jay_bob · #4 02-17-2020, 09:20 AM

The linkage works like this:
There is a shaft that goes into the inside of the exhaust housing. The shaft is rotated by the actuator and linkage.

On the inside the shaft has an eccentric cam. This cam sits in a slot in a ring around the turbo housing. As the shaft turns it rotates the cam which rotates the ring. The vanes are set into the ring at one end. There are pivot points at both ends of the vanes, one at a fixed position and the other in the ring. So when the ring rotates it causes the vanes to open and close.

It is counterintuitive to what you might think is happening, closing the vanes increases the exhaust gas velocity upon the impeller and makes it go faster, just like putting your thumb over a water hose. The vanes don't close 100%. So closed vanes = boosting and open vanes = no (or reduced) boost.

I did have a scare this weekend. I had neglected to properly connect the joint between the silver charge air pipe from the turbo outlet to the muffler in front of the engine when I put everything back together last weekend.

This is the connection that uses the u-shaped sliding plate to hold the two pipes together. I had missed the slot on one side which caused a boost leak to occur. So much so that it was audible. It didn't happen right away or all the time but it caused the car to go into major limp mode (could not rev over 2k and could not achieve more than about 25 mph).

Codes came back 'mass airflow sensor check for power and ground'. Ran the self tests on the MAFs and they had proper response. Then the leak opened up and I could hear it hissing.

Started inspecting things and found that clamp out of position. Took the charge pipe and muffler off and set things properly. Had to re-bend the U-clamp as it was bent out of shape. Running good now.

Also located the source of a nagging exhaust smell in the cabin. It wasn't major, you would just get a whiff sometimes at a red light. Spotted the puff of smoke under the hood and traced it to the EGR valve housing. Found that when the prior shop had done the oil cooler seals they did not torque the EGR bolts to the housing properly. They were loose and it was letting exhaust escape. Was able to get about 1/8 turn on them with my torque wrench (12 Nm) and this seems to have cleared that problem.

Slowly but surely working my way through everything that shop touched and hopefully won't have any more issues resulting from that work.

Just a couple examples of why close attention to detail is required when working on these cars. Simple things like missing a slot or not torquing a bolt properly can cause many issues.

Waiting on MBUSA to activate that sunroof recall so I can get that fixed before giving the car back to my son.

jay_bob · #5 02-17-2020, 05:18 PM

Quote:

Originally Posted by TimFreeh

I've always kind of wondered how in the world a mechanical linkage that is supposed to adjust the pitch of the blades in a turbocharger could possible live for more than about 5 minutes in the environment where its constantly getting pummeled with high-velocity exhaust gas. I'm amazed this is the first time I've ever heard of issues with the associated linkage.

There was nothing broken I guess? What are you impressions about the long-term durability of this kind of setup?

I've got lots of OM648 CDI experience but I've never had to mess with any turbocharger issues, I was aware the OM642 had the variable pitch blade setup - do you know if the OM648 has the same setup?

As far as I know the 648 also has a VNT turbo.

They are quite common in the turbo diesel world now and there are many stories of them failing. Usually what happens is it ends up taking out the gears on the actuator assembly. However my actuator appears to have survived and is working correctly once I cleared out the carbon from the vanes.

There is also a hack fix for this involving spraying EZ-Off oven cleaner in the turbo and letting it eat the carbon. Sorry that is arguably one of the nastiest chemicals available to the general public (NaOH) that has no business around an aluminum engine.

If you have Xentry you can go into the engine control actuations menu and you can cycle the VNT actuator back and forth. Or simply turn the key on and off while watching the arm, it should go up and down. The crank coming out of the actuator box should rotate through about 90 degrees.

There is a thriving Chinese copycat market for these actuators but they are junk so buyer beware if you need a new actuator.

jay_bob · #6 02-17-2020, 05:35 PM

Bill of materials needed for pulling/replacing a turbo. This is all the one-use bolts and gaskets you will need for the turbo support and exhaust side of the turbo.

Qty Needed - MB Part number - EPC Description - (plain english description) - EPC Group/subgroup/callout number (for OM642 in W211.022 chassis)

1 - A642 142 07 81 - Metal Seal Stay to Cylinder Head - (goes between turbo and pedestal) - 09/075/60
2 - A001 990 03 14 - Bolt Turbo on Support M8 x 27 - (these hold the turbo to the pedestal) - 09/075/50
1 - A219 492 00 80 - Flange Gasket to Turbo - (turbo exhaust discharge gasket) - 49/222/70
3 - A000 990 67 03 - Bolt M8 x 20 - (holds turbo exhaust discharge elbow to turbo) - 49/222/80
2 - A642 142 18 80 - Gasket - (used on both ends of EGR 90 deg. tube) - 14/090/45 and 14/090/55
2 - A000 990 69 03 - Bolt M6 x 16 - (used on exhaust collector end of EGR tube) - 14/090/50
2 - N000000 001119 - Bolt M6 x 33 - (used on EGR housing end of EGR tube) - 14/090/55
1 - A642 142 32 80 - Gasket - (exhaust collector to right exhaust manifold) - 14/060/20
1 - A642 142 31 80 - Gasket - (exhaust collector to left exhaust manifold) - 14/060/20
6 - A000 990 68 03 - Bolt M8 x 25 - (exhaust collector to manifolds 3 per side) - 14/060/33

Following are the intake side gaskets if you need to replace them

1 - A642 094 00 80 - Seal Turbo Intake - (big red molded ring from the Y-pipe to inlet) - 09/050/10
1 - A014 997 64 45 - O-Ring - (green o-ring, from turbo outlet to silver outlet pipe) - 09/050/50

jay_bob · #7 05-09-2020, 09:14 AM

So the problem came back a week ago.

Noticed the actuator was hesitating going up and down when I activated it with Xentry. I took the linkage free and the turbo was still moving ok.

Started looking on the web and found a bunch of Chinese clone actuators which I passed on.

I found a complete replacement turbo for $1300, new original Garrett made in France, so yesterday I replaced the turbocharger.

Found on Amazon of all places. https://www.amazon.com/gp/product/B078NHVF7V/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

It was sold through a reseller but I figured with Amazon in between if it turned out bad I had Amazon to go to bat for me with the seller.

It fit perfectly. The only thing I had to do was swap over the exhaust collector flange and the EGT probe.

In order to do this you will need a A642 142 04 81 gasket and 3 more A000 990 68 03 - Bolt M8 x 25 (same ones used on the exhaust manifold flanges).

It is very important to do a dry fit of the turbo first as the relationship of the oil tower bolts and the back bracket bolts will change when you break this connection between the turbo inlet fitting and the exhaust collector.

To do this, put the exhaust collector on the turbo but do not tighten the bolts (get them close but leave them loose enough that the exhaust collector can float).

Put the turbo in place on the oil stand and put the two big T45 bolts in. Don't torque them, just bring them to where they are secure. Now look in behind the turbo and put the two bracket bolts back into the top of the engine. Secure these two bolts.

Now look on the turbo to collector connection you will have a bolt up top that is easy to get to. Tighten this bolt down so that the connection won't move when you remove the turbo. The other 2 bolts are hidden below and impossible to access with the turbo in place.

Remove the 4 bolts holding in the turbo and remove it, being careful not to disturb the alignment between the turbo and the collector.

Torque the 3 bolts down 20 Nm + 90 degrees.

Now you can go ahead and install the turbo. First turn it upside down and put an ounce or two of engine oil in the ports. I turned the impeller back and forth with my fingers to get the oil into the bearings. Then I flipped it over and let the excess drain out.

Once you get everything installed it is important to re-establish the oil flow into the turbo. Easiest way to do this is to disable the engine from firing by unplugging the cam position sensor located on the right side of the engine above cylinder #2.

Crank for about 20-30 seconds to get the oil flowing then stop. Plug the sensor back in and then start the engine normally and let it idle for 5 minutes.

This will set a stored code for cam position sensor failure but does not set a check engine light. It can be cleared with Xentry and I assume with lesser readers.

Took the car out for a drive last night and all seemed to be much better.

benzevo124 · #8 12-06-2021, 09:47 PM

I have a ‘07 GL320 with 255k and the VNT started acting up. At first it would skip a beat every once in a while driving uphill at low rpm and ~60% throttle. It progressively got worse to a point where I lost boost completely, no down shifts, check engine light.
When I disconnected the arm from the controller and moved it back and forth it would get sticky in the up position.
I’m trying to figure out if this is a carbon build up issue or if the turbo needs rebuild/replacement.
Any help or advise will be appreciated!
-Pete

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jay_bob · #9 12-10-2021, 01:00 PM

My experience was the turbo got carbon deposits. It caused the actuator to get stressed out trying to move the linkage to overcome the friction.

So I took the turbo apart and cleaned it but the damage had been done to the actuator.

Remember that there are many torque-to-yield (i.e. single use) bolts and also gaskets that cannot be reused. If you pull the turbo you have to replace the gaskets and bolts or else you will be having trouble with leaks or snapped bolts later on.

benzevo124 · #10 12-10-2021, 02:04 PM

Cool, so there's hope!
My actuator still works fine since it only gets stuck at full boost, it moves freely otherwise. I ordered a turbo replacement parts kit from FCP euro.
Did you have a problem with the bolts on the turbine housing? Do I have to apply heat or just soak them in PB blaster to remove?

jay_bob · #11 12-10-2021, 11:19 PM

No it came apart very easily.

benzevo124 · #12 12-18-2021, 01:06 AM

I pulled the turbo today. It’s in pretty good shape. Keep in mind this car has 256K on it.
At first look the vanes only had a light coat of soot which I was able to brush off with a toothbrush.

No visible signs or indications why it would stick open until I dug further.
To open the VNT housing I had to remove 5 small T-25 screws. Breaking the first one was discouraging but I took my time on the rest and soaked them with PB blaster. I had to go back and forth a number of times to prevent them from snapping.
The internal part had thicker carbon deposits that were more crusty.

These parts also cleaned up pretty nice with a small ss wire brush.
However the arm was still sticking. The problem was the soot got into the spot where the shaft goes through the turbine housing. I sprayed the area with PB blaster and worked it in until it soaked through the other side.

Before reassemble, I wiped everything dry and used a torch to burn of any remaining blaster residue. Putting it all together was a bit challenging.I had to put all the parts into the housing first than lower the turbo onto it carefully aligning all the pieces.
Everything moves freely now without binding.
Sorry about hijacking your post, I figured it would be useful to others as I haven’t seen much documentation on cleaning these turbos out. Most of the youtube videos are for VW tdi’s and Ford’s.

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Murkybenz · #13 12-18-2021, 07:50 AM

Caustic based household limescale removers , oven cleaners / shower etc will eat the carbon deposits away very nicely.

jay_bob · #14 12-28-2021, 12:47 PM

Quote:

Originally Posted by Murkybenz

Caustic based household limescale removers , oven cleaners / shower etc will eat the carbon deposits away very nicely.

Agreed, just remember to only do this on the turbo housing itself, away from the engine, as this stuff will absolutely destroy the aluminum intake manifold or head if you try to do this while it's still in the engine.

And again I will reiterate that you do not want to put any kind of lube on this assembly as it will either decompose in the heat or attract more soot.

benzevo124 · #15 01-01-2022, 05:16 PM

After cleaning the turbo I also installed a new VNT actuator. On the first test drive everything was back to normal, good boost all is well.
Then after longer drives around town I started noticing strange sounds coming from the engine bay. It's hard to describe but it sounds like I had installed an aftermarket blow off valve but not all the time. Normally when I would come to a stop sign or take my foot off the throttle I would hear a "hiss" or "psshh" sound. But now after a longer drive when the engine gets up to normal operating temps the "hiss" turns into a much louder "k-kahh" sound. On occasion I've also noticed a momentary misfire like hesitation. One time after I got home I let the car idle on the driveway and out of nowhere the engine got louder, it was coming from the air inlets behind the grill, same kind of 'kahh" turbo noise but constant. It went away after I revved the engine one time. No codes or check engine light.
Is it possible that some other components were damaged while the VNT was acting up and over boosting or do I have to bite the bullet and buy a new turbo?