Engine stutter followed by limp mode (ML320 CDI - 2006, W164)

[MikeNorth]

Hi there, I recently purchased a 2006 ML which drove fine, during the test drive. However, when I took it home, the ML lost power (limp mode), following a series of shudders / stutters. Having had an independant merc mechanic run star diagnositics, it highlighted an issue with the EGR, which we replaced. This did not resolve the issue. We then found out that someone had blanked something (using a resistor - not sure what), so we then went to the hassle of changing both inlet manifolds, as they are a known issue at that mileage (116K). Again, this did not fix the issue. The star diagnostics does not show up any issues...

...any ideas?

 

[Larkone]

turbo actuator - can cause kangarooing and doesn't throw codes. Can be re-furbed or only replaced with exact same as they are matched to the turbo.

 

[MikeNorth]

@Larkone - having looked through a number of potential options, that was one of the two I had narrowed it down to: Throttle position sensor was the other. I am now also seeing the glow light stay on, so I am wondering if I also need to invest in a Glow Plug Control Unit (because the previous owner 'allegedly' changed the glow plugs recently)...

 

[oigle]

Someone may have attempted to delete the egr function. Not an unusual thing to do, given the problems the egr can cause. Might need to work out what has been done. Blanking it off will cause limp mode. Has to be done electronically or by mapping to be successful.

 

[Larkone]

I think he means that the swirl flap motor was bypassed using the resistor fix.

 

[MikeNorth]

@oigle We replaced the EGR under the Mercedes exchange scheme and then ensured it was active via Star diagnostics. We thoroughly tested it. Once we did that, and the EGR would open, the car would either stutter or stall. That’s when we realised the inlets had been blanked. We changed them and removed blanking (via resistor). Again, issue still there, sadly and frustratingly…

 

[MikeNorth]

I think he means that the swirl flap motor was bypassed using the resistor fix.

Correct - we then exchanged entire inlet manifolds and motor(s)

 

[Doug1234]

If it has a bad turbo actuator or the vanes are sticking in the turbo you will get shudders / stutters.
Same engine in my Jeeps been doing it and now running with actuator disconnected and lever for the vanes on turbo tied up in up position ( well just to hold it as its seized solid) until I fit a new turbo.
I find it really odd the Mercedes do not flag up the actuator , the Jeep would flag that first then a few minutes later the egr ... PO403 accompanied by a slight hissing. Clear codes and runs ok but never over 2k revs or it stutters a bit then egr code comes back .
My actuator is good as the stored code for it cleared after I disconnected the arm from the turbo... but if the Merc’s will not flag the actuator up as bad then egr code is the first one you will find when its not actually anything wrong with the egr its just flagged the code due to ecu seeing weird airflow.
Swirl motor was probably what the resistor was for.
Disconnect the actuator from the turbo and work the linkage on the turbo up and down to feel if its tight anywhere.
Was the actuator tested when the diagnostics were run ?.

 

[MikeNorth]

If it has a bad turbo actuator or the vanes are sticking in the turbo you will get shudders / stutters.
Same engine in my Jeeps been doing it and now running with actuator disconnected and lever for the vanes on turbo tied up in up position ( well just to hold it as its seized solid) until I fit a new turbo.
I find it really odd the Mercedes do not flag up the actuator , the Jeep would flag that first then a few minutes later the egr ... PO403 accompanied by a slight hissing. Clear codes and runs ok but never over 2k revs or it stutters a bit then egr code comes back .
My actuator is good as the stored code for it cleared after I disconnected the arm from the turbo... but if the Merc’s will not flag the actuator up as bad then egr code is the first one you will find when its not actually anything wrong with the egr its just flagged the code due to ecu seeing weird airflow.
Swirl motor was probably what the resistor was for.
Disconnect the actuator from the turbo and work the linkage on the turbo up and down to feel if its tight anywhere.
Was the actuator tested when the diagnostics were run ?.

I am no sure, TBH. The independent Merc mechanic is coming back in the coming days. I’ll ask the question then. Just worried about spending more money, replacing more parts, without actually resolving the issue. It has become a money pit

 

[sweeper]

My R Class suffered occasional lack of power with no fault codes, eventually it did throw one up relating to the exhaust pressure sensor, this is the one that measures exhaust pressure before turbo, there is a service bulletin relating to the contact on this sensor, if you can read the data coming from it it may be all over the place like mine was, even when I was getting full power, i saw at one stage it read 0000kpa, i didn't bother with the contacts and just replaced the sensor, no more issue so far and if reading the live data it is stable, oddly when I mentioned the fault to an independant his first reaction was egr,

 

[MikeNorth]

My R Class suffered occasional lack of power with no fault codes, eventually it did throw one up relating to the exhaust pressure sensor, this is the one that measures exhaust pressure before turbo, there is a service bulletin relating to the contact on this sensor, if you can read the data coming from it it may be all over the place like mine was, even when I was getting full power, i saw at one stage it read 0000kpa, i didn't bother with the contacts and just replaced the sensor, no more issue so far and if reading the live data it is stable, oddly when I mentioned the fault to an independant his first reaction was egr,

Thank you - I’ll add that to the list of ‘to be checked’ by the Merc mechanic…

 

[Larkone]

TBH any good MB indy should know all of these faults and fixes because the OM642 engine is used across the range. Really surprised your MB mechanic is struggling with this. Put up your location and someone may know a recommended indy in your area.

 

[MikeNorth]

TBH any good MB indy should know all of these faults and fixes because the OM642 engine is used across the range. Really surprised your MB mechanic is struggling with this. Put up your location and someone may know a recommended indy in your area.

Location is Bracknell (RG12 8). This Indy was actually recommended, by a couple of friends, but I am second-guessing those recommendations now :-/

 

[Taffy7hfa]

If its not storing any dtc's the next step would be to go through all the live data whilst hooked up to Star.
Absolutely no point in guessing and throwing parts at it. It cannot be in true limp mode without there being a stored or active dtc, it's just down on power, there are many things that could cause that.

 

[Wighty]

Location is Bracknell (RG12 8). This Indy was actually recommended, by a couple of friends, but I am second-guessing those recommendations now :-/

Is Ian at Star Mercedes , Caversham , Reading , any good for you (MB specialist)

 

[alexanderfoti]

You can normally tell by driving them whether its the actuator or the backpressure sensor, but the backpressure sensor is cheap and easy to chance, so if they are unsure, they should just do that first.

As others have said, monitor the values whilst its doing it should indicate which is at fault.

 

[MikeNorth]

If its not storing any dtc's the next step would be to go through all the live data whilst hooked up to Star.
Absolutely no point in guessing and throwing parts at it. It cannot be in true limp mode without there being a stored or active dtc, it's just down on power, there are many things that could cause that.

Thanks for your advice. I know that the issue occurs when you drive carefully, on country roads. It feels like the car wants to shift gears, then judders. I can counter this by accelerating suddenly, but after time, typically at traffic lights, it will ‘clunk’ down a gear and from then on, it will not allow me to exceed just over 2K RPM. If I turn off the engine, wait a minute and start it again, it drives fine again, but not for long…

 

[bembo449]

ive done several actuator repairs on this unit , I use turbovanes in Birmingham , brilliant service with quality product , I'm concerned reading your replies that even though you were advised to look at the actuator very early on in the thread , you have not done so ! this in my opinion should have been your first job , then look at other things if it didn't cure the issue

 

[MikeNorth]

ive done several actuator repairs on this unit , I use turbovanes in Birmingham , brilliant service with quality product , I'm concerned reading your replies that even though you were advised to look at the actuator very early on in the thread , you have not done so ! this in my opinion should have been your first job , then look at other things if it didn't cure the issue

Hi there, I only initiated the post / thread yesterday. I am amazed (and pleased) by the number of replies and the great advice shared. I will ask my Indy to carry out active tests, whilst the vehicle is driven. Hopefully it’ll identify whether it’s the back pressure sensor, or actuator…