kimt

Hi,


Since we purchased our brand new GLK 250 CDI about a year ago, the transmission upshifts extremely slow and far too late. If you're accelerating very very slowly, it shifts up (as it should) at about 2200-2400 rpm.
However, if you press the accelerator a TINY bit more, it shifts far too late. The transmission simply refuses to use the available torque of the engine at low rpms.
Even when pressing the accelerator far less than half, it'll only shift at 3000 rpm or above. We shortly drove a ML 250 CDI by way of comparison, which has a completely different (i.e. normal) shifting pattern. In fact any other MB we ever drove, shifted as a modern automatic tranny should.
The only way to drive the GLK 250 CDI in a more or less acceptable way, is to upshift manually... The difference between the normal and sport mode of the transmission is extremely small (about 200 rpm difference in shift point).
We have the impression the transmission software interprets the actual position of the accelerator completely wrongly.
It's really a pity for an otherwise very good car with a brilliant engine. Any driving pleasure is completely killed by the terrible transmission.
Anybody experienced the same problem and if so, was the dealer able to remedy the problem?

Kimt

fabbrisd1

As a general comment - are you aware of the "left-3-sec-pull/hold" feature on the transmission - ues, you can "click" down one gear - but if you pull/hold for 3 seconds then the tranny will downshift/jump to the passing gear for that speed - a "right-pull-hold" for 3 sec will return to auto.

Procedure also useful to downshift/multiple gears for deceleration... adding engine braking power such as downhill exit ramps and the like..

This procedure applies to gasser or diesel equally...

Have fun with it.. keep the beat !

kimt

Thanks for the reply.

Yes, we know that feature for quite some time and find it handy if you want to overtake quickly (e.g. in my CL 63 AMG)
The problem I've been describing above is a completeley different issue. We usually drive the GLK 250 CDI in E-mode and even in that "normal" mode it upshifts far too late.
It'll upshift however every time you pull the right paddle (only above 2000 rpm, otherwise it'll neglect the command to upshift unless you're in manual mode), but this is not really the way you want to drive a diesel car which has plenty of torque from about 1750 rpm.... The logic of the transmission software should be adapted to the engine charastics which in this particular model clearly is not the case. The same comment by the way holds for the GLK200 and GLK 220 CDI with 7G-Tronic transmission.


Kimt

LesF

MY glk250 (early 2013) is in the shop now for fuel injector problems and I had asked them to look at this very issue. It seems this problem manifests itself on start up when the engine is not at a normal operating temperature.

Maybe the program is designed that way so you reach operating temperature a bit faster which makes for better fuel mileage. I would rather be able to control the transmission up shifts.

107123210

The GLK250 is new to us, but I have noticed something similar.

We are staying at present in a gated community. To keep speeds down, they have speed bumps at regular intervals. WE have to come to almost a standstill at each bump. But then when I try to accelerate back up to speed, the engine does not respond. It almost feels like it has cut out, but in fact it just has a huge lag. I am using E-mode and not using the paddles. I have tried switching to S-mode and it helps a little.

The car has much less oomph off from a standstill than my 85 300D.

Is this normal behaviour for this car?

Or is it a learning process? I know that when I first bought my 85 300D about 21 years ago, it took a while to,learn how to get the best out of it.

bytemaster0

Let's not forget that although the 2.2 diesel engine's TORQUE is available at low RPMs, its HORSEPOWER peaks well above that. So, your GLK is doing exactly what it should to achieve high-end acceleration. Horsepower is the rate at which work is done. In this case, torque multiplied by distance over time.
So, while having 369 or so ft-lb of torque at low RPMs is a GREAT experience at a certain RPM range, you eventually have to move the crankshaft faster. As the torque curve begins to drop, the speed increases, so the HP curve finds a middle-ground at a higher RPM.

Think about this: A human being, at maximum exertion on a crank pedal, can actually achieve MORE than 400 ft-lb of torque! However, this is at or near zero RPM. Start going faster, and humans peter out quite quickly. I'd say that past 30-50 RPM, a human's torque decreases dramatically. The 2.2 engine, on the other hand, has its 369 lb-ft of torque available at a much higher RPM range, which is why it can get a 2-ton car moving much, much faster than a human could. And, which is why it has 200HP, versus the 1.2 HP that a human can momentarily produce.

Work, and rates, plus the fact that we don't have a continuous transmission, all go into this equation. So, while your brain is telling you that yes, your transmission should be upshifting earlier to take advantage of all that torque, if max acceleration is your aim, the engine should be allowed to go up in RPMs.

Your transmission is making a great tadeoff between responsiveness and fuel efficiency. I personally would prefer that it upshifts earlier too, when I'm lightly pressing the pedal. But I think it can learn that over time. My only question is, does use of Distronic Plus affect transmission shift time learning (Distronic Plus tends to upshift very late in order to produce consistent power, and respond better to traffic), or is it kept independently of driver inputs? Would be interesting to hear some thoughts on this.

mjhawkins2346

I would try disconnecting the battery for a few minutes to force the ECU to re-program itself. That failing perhaps the dealer can re-flash your ECU with the latest software. Just an idea - might be worth trying.

Purell

I drive a 2013 GLK 250 and also experience the symptoms described by the OP. This happens even when the engine is warm. At the higher engine speeds, considerably less power is felt, to the point where I feel little acceleration available. To counter this, I typically use the paddle up shift or release the gas peddle entirely momentarily, which causes an up-shift. Doing so, drops the revs and returns the torque expected (and loved) from a diesel. I have not discussed with the dealer as I just accepted it as the design, but this has always irritated me. Glad someone else feels that this is an issue and would be nice to hear of a solution from MB.

fabbrisd1

To be of some help - there is a general misunderstanding about "E" - since "E" mode is actually desinged for open highway driving where the programming objective is to get you to the highest gear possible as readily as possible - has nothing to do about general fuel economy - E/S are for particular driving conditions - "S" being standard, for driving en****ered in "noraml"/city/neighborhood driving - yes, open highway driving gies higher fuel economy - as noted by such testing standards such a US EPA - however, using "E" for city/neighborhood driving is a "mismatch" from the get-go.

Unclarified MB manuals conitued year after year and model after model admittedly contribute to this continued broad-prevalent-nonsensical misunderstanding of E/S.

mjhawkins2346

Where did you get this information? I'm on my 9th MB and have never heard it. You could be exactly right but I would love to know more about the transmission mapping.

107123210

The GLK manual describes the characteristics of E and S quite clearly.

E causes starts in 2nd gear and higher gear ratios For that reason slower engine rpm which transfers to better mileage under many conditions, thus presumably the E for economy.

S is for SPORT mode. Starts in 1st gear for sportier take-offs and lower gear ratios overall. This translates to lower mileage.

Makes sense to me and no different from another benz I own.

kimt

Thank you all for the replies.

I got an official reply from MB which boils down to the fact that they say that the vehicle is technically as per spec and that the transmission has been tuned that way to optimize CO2 emissions.
Hard to understand why higher revs before shifting would lead to better CO2 emissions especially if you take into account that EVERY OTHER MB VEHICLE SHIFTS MUCH EARLIER.
I drove a ML 250 CDI back to back with our GLK 250 CDI. The ML 250 CDI, being a NEWER vehicle and surely also CO2-optimized, shifts a lot earlier.
Therefore I simply don't buy that argument from MB which means that we remain frustrated in this lazy transmission.
Fortunately our dealer is very cooperative which means that we might end up buying a 2015 GLK in case we get an interesting proposal to trade ours in.

Kimt