dannyfiveforty

I have a 2011 350cdi bluetec and have a couple of niggles.

1) does yours shift harshly from 1-2 and 2-1 ?

2) do you notice a slight judder/shudder/almost kangerooing sensation when the car shifts from 5-4, 4-3 when the car downshifts due to the revs being too low, I.e going uphill under light throttle?

3) do you notice the throttle pedal/input is sometime unpredictable and can be hard to get the desired acceleration sometimes? Ie pedal position doesn’t always seem to be the same every time and sometimes it needs to pressed further than other times and vise versa? And then other times you press it a small amount and it suddenly changes down a gear and launches forward?

thanks

artim808

1) are you using economy or sport mode when you experience this issue?

2) Don't know, I need to test that

3) Did you recently purchased this car? I had same "issue" when I purchased the car but replacing the air filter, fuel filter and ECU reset seems help. You want to reset ECU so the car will learn your driving style.

dannyfiveforty

Ok thanks, it does it in all modes. Yes give it a go I would be interested to see if you notice it. Best noticed going up a slight hill, light throttle and let the revs be low to let the car naturally want to change down, keep your foot in the same position on the throttle. I have had car a couple of years and sometimes it seems worse than others. I have replaced filters already. What is the ECU reset procedure?

thanks

artim808

For ECU reset just use any obd scanner, connect to ECU and click erase trouble codes. Even if there are no codes stored, this will reset the ECU.

For TCU reset just follow these steps, it's very easy:

1. Turn the ignition key to the on (not start) position.
2. Press the gas pedal to the floor and hold for 30 seconds.
3. Turn the key to the "off" position (don't remove the key), then release the gas pedal.
4. Wait at least two minutes for TCU to reset.

Here is video how to do it:

dannyfiveforty

Ah yes, that resets the learnt shift patterns doesn’t it, I have done that, I have also cleared all fault codes using my scanner. The problem still persists.

thanks

Bklyn

Any chance you can take a moment and tell me what ECU is? Is it only for Bluetec cars?

Bklyn

GREAT video BTW! Thanks

artim808

ECU - Engine Control Unit
Every modern car have it.

Bklyn

Thanks. I will read about it.

dannyfiveforty

Anymore bluetecs in here with similar driving symptoms?

thanks

KiloWatt

The OM642 engine (S320CDI, S350CDI) is known to be a somewhat problematic combination with the 7G when it comes to smoothness of shifting. The problem is that the real, exact torque of this engine is hard to calculate in many situations.

MB even replaced my 7G during warranty after countless attempts of changing injectors, software updates, flushing, adaptations did not help. The "new" 7G was better. But the basic "problem" has persisted as you described it until this day. Maybe not at all as bad as you experience it. Hard to tell because it is subjective to some degree. And there cars with this combo that are just worse in shifting comfort than others for reasons nobody knows.

As the 7G continuously adapts itself, it can be different from day to day. And moreover these Diesel engines can deliver very different unpredictable torque to the 7G depending on particle filter regeneration, temperature, etc. that just "surprise" the tranny.

As the combination apart from these quirks is really fantastic, and was class leading when it was launched, I just accept it as it is and try to be careful not to provoke these problems during driving.

KiloWatt

The kangarooing in the upper gears can be a dirty exhaust (I think O2 IIRC) sensor, due to driving at low engine load for longer periods of time, many cold starts, poor diesel quality, etc. Try cleaning it by driving at high engine load (Autobahn ) for 100km+ or clean it manually. That helped every time I experienced this.

dannyfiveforty

Many thanks your very informative reply. It feels almost as though if the torque converter would allow a lot more slip the car would be a hell of lot smoother? but I guess this to do with emissions? The kangerooing is only very slight and only when the car has just changed down a gear at low load, usually noticed on an incline at low revs. It is exactly as you say, different from day to day. And noticeably different when the dpf is regenerating, - the tiniest of throttle adjustment can feel like a hesitation, again, I am sure more slip on the TC would prevent this.

Thanks

MercNorway

As to your number 2), I had a R class with same engine/tranny combination. On this car I had this sensation; almost like it struggled a little bit to downshift only when light trottle / low revs. You could feel a litlle "shiver" in the car before it eventually shifted down. Got a diagnose and it came up with a code which I think said something like "converter friction to high" or something like that. Had to replace the converter, but I traveled to Germany and raplaced the whole tranny with a refurbished one since that was only marginally more expensive than replacing only the converter here in Norway. (2500 $ +).

dannyfiveforty

Thanks, Not sure if yours is the same symptom, mine 'shivers' as soon as the lower gear has engaged, and not prior to it shifting..( for example if it was a manual car and you changed from 4th to 3rd at approx 1000rpm, clutch down, into 3rd and as the clutch comes up and bites the 'shiver' is there.

Thanks

KiloWatt

Yes, exactly, emissions/fuel economy, performance and shifting comfort are antagonisms when it comes to automatic transmissions. Hard for any manufacturer to achieve this 100% perfect nowadays. The newer 7G generations were a little better but often far from perfect with the OM642. Even the early 9G struggled a bit (I have frequently loaners from the MB dealer). However, I drove a GLS with that engine late last year, and it was virtually perfect! So, not to far from the end of the OM642 (and the GLS) it seems they had sorted these issues out completely.

When we tried to fix these issues under warranty long ago, the dealer even involved an expert under direct control from the HQ in Sindelfingen who came many times to sort these things out! Great support by MB and the dealer!!! As I am usually quite attentive, I guess they thought I would be the right guy to see how far these things can be fixed. First thing he did was to actually make sure the engine runs as good as possible as it has a habit of surprising the tranny.

Your kangarooing seems exactly as mine. The hint regarding the dirty exhaust O2 sensor came from that MB expert actually. Usually there is NO fault code. It just needs to cleaned one way or the other. And: neither the engine nor the 7G seem to like extremely gentle driving. A little power (without being aggressive) now and then could help.

Adaptation of the 7G usually lasted only a couple of days for me. So if adaptation is not totally off, I guess it is a waste money many times.


The good news is that these issues have not gotten worse at all over the last 10 years and 200000 km! Just make sure to change tranny oil every 60000 km or so. I never flushed, just the regular MB specified oil change. I would only flush it with cleaning agents in an attempt to salvage it, if the 7G has more severe issues.