acceleration problem

keithcdi220a

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Hi.
I have an acceleration problem, when I start off the car accelerates ok, but once in top gear there is no rapid acceleration available. The car just very slowly picks up speed, I have to lightly depress the accelerator to get up to speed. Out of gear the engine will rev up to the red zone. I am wondering if this is an auto gearbox problem as it is like it is in limp mode. I paid for a diagnostic check but no codes were shown.:dk:
 

MancMike

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You have to lightly press it to get up to speed? There's your problem.

What happens if you floor it in top gear? It should drop gears and pick up? If not, maybe follow the TCU reset procedure as it learns your driving style and may have gone to sleep a bit.
 

renault12ts

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Usually limp home mode is less to do with the gear box and more to do with the engine. Is it smokey at all?
 

kid-jensen

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Automatics are pretty clever but you can't give them mixed messages.

If you're in top gear, the car is not going to accelerate swiftly, because that's not what top gear is for! It's for better economy and low noise..

If you want to get a move on, kick it down and get the most appropriate gear automatically (see what I did there?).

Basically, the car is behaving how it's designers intended..
 

renault12ts

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Automatics are pretty clever but you can't give them mixed messages.

If you're in top gear, the car is not going to accelerate swiftly, because that's not what top gear is for! It's for better economy and low noise..

If you want to get a move on, kick it down and get the most appropriate gear automatically (see what I did there?).

Basically, the car is behaving how it's designers intended..
I suspect it hardly moves in top which it should do using the torque of the engine. It's in limp mode. When this happened to my (diesel) it was a clogged egr.
 

renault12ts

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Surely if it was in limp home mode, the OP would notice lack of acceleration in all the gears?
We'll know more...if he comes back.
 
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keithcdi220a

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i-CONICA nothing hapens if I floor it hence the gradual pedal pressure to increase speed.
PaulG it does not acceleraste at all unless is coaxed by gentle pedal pressure
renault12ts It does not smoke and revs freely when not in gear.
The gearbox does change up and down ok.
It seems more like lack of power as when it comes to a hill it just will not accelerate to take the hill.
As I mentioned when I start off the car accelerates rapidly, but once in top gear there is no rapid acceleration available.
It is going to a specialist diagnostic centre in Newark who just do diagnostics. So it will be interesting to see what they come up with.
 
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LvR

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I paid for a diagnostic check but no codes were shown.:dk:
Paid for a STAR check and no codes shown?

.....................but once in top gear there is no rapid acceleration available.
Is this a new condition?

How long have you owned the vehicle?

My guess is that this is to be expected because of mechanical and physical limitations of the engine. If you want to be sure stick it on STAR and drive around while monitoring realtime data on the ECU and TCU.


However - this statement is in direct contradiction with
i-CONICA nothing hapens if I floor it hence the gradual pedal pressure to increase speed.
and
The gearbox does change up and down ok.
.................. because if you "floor it", the ECU and TCU should sense the need for the extra demanded power and kick down automatically - if you floor it and no kickdown happens it cannot possibly be shifting ok.

"Gradual pressure" causes acceptable acceleration but flooring it doesn’t, simply doesn’t compute - STAR will tell you what is going on
 

GeeJayW

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Sounds to me like it is in limp home mode. Had this on my Golf when the EGR valve got stuck, though of course there are a number of potential faults that can put the car in limp home. There should be some fault codes IMHO.

Where did you get it scanned?
 

PobodY

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If the car accelerates in the other gears, and the gearbox is otherwise fine, is it as simple as no kick-down?
 
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keithcdi220a

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Ah well that identified the problem. The Turbo has seized probably due to carbon deposits. The turbo is an electric actuator model. I have been in contact with a specialist Turbo repair company. He described my fault exactly,and said it wold not show a fault code even on Star. So that saved me £136 diagnostic cost by Mercedes Peterborough. He gave me a cost of £298 for free collection & return within 48 hours. repair it to better than OEM, all coded ready to go also gives a 24 month guarantee.
 
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LvR

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Ah.................... He described my fault exactly,and said it wold not show a fault code even on Star. ............
Indeed .............. possibly ............... but do note STAR is not only a code reader - with STAR you have access to any and all instrumented parameters on the vehicle, so if you would have queried at least the intake manifold pressure and MAF rates via STAR on your vehicle, it would immediately have been obvious you are not getting any boost at all.

Still wondering about the "paid for a diagnostics check" and what exactly got diagnosed/checked. .........cost of "check"?
 
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keithcdi220a

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Hi LvR
£36 cost as a favor at specialist diagnostic center in Newark where the sized turbo was identified.Turbo has now gone off to the specialist turbo company in Stoke, should be back and refitted to the car next week.
 
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