OM642 VNT Turbo actuator issues - PeachParts Mercedes-Benz Forum

jay_bob · #1 02-02-2020, 02:20 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.