Acceleration 'lag/ delay'.

[markjay]

Old thread revival...

I now have the W204 (MY 2013/ facelift) - it's the C180 with the 1.6L Turbocharged M274 engine and 7G-Tronic Plus automatic transmission.

The car seems fine for taking-off at traffic lights etc - no transmission delay there - but it does have one other peculiar behaviour.

When using kick-down (something I only very rarely do...) from standstill or low speed, the car will drop a gear correctly, then accelerate with the rev reaching the red line, as it supposed to do. So far no problem.

But instead of shifting-up as soon as the red line is reached, it then 'hangs' on the rev limiter and stays on the red line for further 2-3 seconds before finally shifting up to next gear.

The driver experience is one of sudden acceleration, followed by unexpected brief braking, then further acceleration.

Obviously, the car does not actually brake, but when the steep acceleration curve suddenly goes flat for 2-3 second, it feels like braking.... though in effect the car simply suspends the acceleration and maintains same speed before finally shifting up and continuing to accelerate.

My passenger thought that I was being indecisive, i.e. that I stepped on the accelerator, then levelled off, then stepped on it again. This is how jerky if felt. It did not feel like something an automatic car should be doing - you'd expect the acceleration to be more or less linear with only very brief minute suspension at shift-ups.

I had the car since February this year, and only ever needed to use the kick-down in this way on two occasions so far (sad, I know ), and on both occasions it did just that.

It does not feel like a fault as such... though a software update to the TCU might resolve this?

Any ideas? Anyone experienced same?

 

[Flackadder]

My 7 speed W204 does not have a delay. To be fair I have never booted it.....standard quite quick gettaway has no lag before initially moving at all. I imagine that if I floored it, it would have a fag and a coffee before moving off.....probably.

 

[markjay]

My 7 speed W204 does not have a delay. To be fair I have never booted it.....standard quite quick gettaway has no lag before initially moving at all. I imagine that if I floored it, it would have a fag and a coffee before moving off.....probably.

The original lag I had with the 5-speed W203 is no longer evident with the 7-speed W204.

However as per my previous post, on kick-down from standstill it won't shift up beyond 2nd gear for a good 2-3 seconds, meaning the engine 'hangs' on the red line and the acceleration briefly goes 'flat' before finally shifting up.

 

[KeithJG]

Don`t forget you now have 1.6 litre so it is hanging on for dear life the revs to give you the most that you are requiring from it?

Perhaps you should ease the throttle as you approach the red ine and then it would sus out less load and change up?

As you know completely pointless going to the red line line regularly as it just causes stress on the parts for no reason at all as you are going no where fast!

.......................

About this lag thingy .....i have never experienced it because i am in S mode all the time so the ECU know`s full well that i mean business. When i bought the motor i used C mode which gave me a leisurely drive with laggish moments which surely are part of taking it all easy.

If one reads the handbook Mercedes actually recommend S mode as the normal everyday mode to be in.

 

[Flackadder]

The original lag I had with the 5-speed W203 is no longer evident with the 7-speed W204.

However as per my previous post, on kick-down from standstill it won't shift up beyond 2nd gear for a good 2-3 seconds, meaning the engine 'hangs' on the red line and the acceleration briefly goes 'flat' before finally shifting up.

Yes, I agree.

As I said before, I have never booted it.Tthough when I have been close to a traffic light burn-out, I have noticed a tendency for the gear box when changing from 1st to 2nd to appear to need to consult the owner manual before it decides it will change gear. This is not at all evident when moving away at a very brisk rate.

 

[markjay]

Don`t forget you now have 1.6 litre so it is hanging on for dear life the revs to give you the most that you are requiring from it?

Perhaps you should ease the throttle as you approach the red ine and then it would sus out less load and change up?

As you know completely pointless going to the red line line regularly as it just causes stress on the parts for no reason at all as you are going no where fast!

.......................

About this lag thingy .....i have never experienced it because i am in S mode all the time so the ECU know`s full well that i mean business. When i bought the motor i used C mode which gave me a leisurely drive with laggish moments which surely are part of taking it all easy.

If one reads the handbook Mercedes actually recommend S mode as the normal everyday mode to be in.

'Perhaps you should ease the throttle as you approach the red ine and then it would sus out less load and change up?' - this is how I normally do it, I rarely use the kick-down flat out, which is I why I did not notice it before. It's not really an issue as such, but it feels more like a software bug than some sort of clever design....

'About this lag thingy .....i have never experienced it because i am in S mode all the time'

I always drive in S mode, not for performance but because the 1.6L feels totally gutless in C, and the shifts are more noticeable - it's not 'comfortable' at all in C.

 

[markjay]

Just to add.... with the 5-Speed on the W203, on the rare occasion that I used kick-down, I kept the foot on the accelerator until it shifted up again, then eased off and proceeded normally.

Which is why I was surprised that the 7-Speed does not do that - as said, it just hangs on the red line and does not shift up for a while, which is odd and also makes no sense as the car stops accelerating. Surely 'slow' acceleration at a higher gear is better than no acceleration at a lower gear?