Over revving - Ford C-Max Forum
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post #1 of 21 Old 12-23-2008, 05:03 PM Thread Starter
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Hi all. Still getting used to my new C-MAX, and enjoying it immensely. However,I have noticed that the car is 'over revving' e.g. from changing from 4th to 5th then giving it quite a bit of gas, the car tends to rapidly rev to 3,000 RPM before settling back down to what it should be. It's almost as though it's taking a second to find the gear when I shift upwards...

This might sound like a daft question, but is it something to be concerned about, or is it me not giving myself the chance to get used to drivinga turbo diesel (having come from a 1.25litre petrol fiesta).

It is still under the car dealership's supplied warranty, so please let me know if it needs to go back!
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post #2 of 21 Old 12-23-2008, 06:42 PM
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Do you keep you foot rested on the clutch pedal? The pedal is very light & any pressure could cause clutch slip.Just a thought.



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post #3 of 21 Old 12-23-2008, 07:07 PM
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Does it only happen at that particular "up shift" or at all of them




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post #4 of 21 Old 12-23-2008, 08:41 PM Thread Starter
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Thanks for the responses guys...

No, I am making sure that my foot is well away from the clutch!

The problem seems to be most noticable from 2nd to 3rd, 3rd to 4th, and 4th to 5th, particularly 4th to 5th though. Been doing my research, and I've not found any conclusive answers to this. I hope it's something as straightforward as transmission fluid replacement.. or maybe something more sinister as a ECU problem.!?
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post #5 of 21 Old 12-24-2008, 06:47 AM
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Sounds like a problem I had on my first CMAX. Which was a second hand car. it was the clutch release bearing. this was the third time it had happened within 12,000 miles. when going back throught the cars history it seems the car had a dented sump, how i never found out,not seen due to the sump guard. the vauxhall garage in wolverhampton forgot to mention this!!while talking to a ford engineer later he told me that the clutch release bearing was proberly taking the strain of the engine now being slightly mis-a-lined. so beware KA04UWU, A 1.6 TDCI.
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post #6 of 21 Old 12-24-2008, 09:03 PM
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Having thought about this a little more since

It's not a simple as transmission fluid replacement

Given that the clutch and the gearbox is fully bolted to the engine via the "bell housing" they should all move together if "thumped to any degree

Even then any misalignment would only happen when the clutch was effectively fully engaged and there would be the smell of the clutch getting VERY hot

Are you sure you haven't got any smell of the clutch getting hot

Given that it is diesel I am wondering about the EDC (Electronic Diesel Control) that replaces the mechanical govenor for the fuel pump but again this is limited by the amount of clutch slip

There is a closed loop control system that involved the accelerator position sensor the injector pump speed sensor and the injector pump "fuel rack" position sensor

On depressing the accelertor the voltage on the sensor changes which causes the ECU to change the position of the fuel "rack" and thus to measure the voltage at the fuel pumpspeedsensor (engine speed as it is driven directly from the cam shaft) based on the stored values in the ECU for that speed and air flow measured from the air flow mwter and input air temperature sensor

It might be well worth having it checked




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post #7 of 21 Old 12-24-2008, 10:15 PM Thread Starter
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Thanks Certed and Richard.


I think with all said and done, I will take it back asap to have it checked. My wife and I both drive the vehicle, and we have both noticed this fault since purchase.Having given it some time to ensure it was not how we were both driving it (being a new car to us etc), it definitely is a clear problem.Your responses have helped greatly in gaining an idea on what might be the cause.

I will let you know how I get on once I get it back to the dealership.

All the best.
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post #8 of 21 Old 12-24-2008, 11:50 PM Thread Starter
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Excuse the further post so early on Christmas Day but this issue is playing on my mind!

Just found this link..

http://forums.moneysavingexpert.com/showthread.html?t=1159131

and the OP's fault sounds similarish to the one I am experiencing.

So my questions now are..

Is it simply turbo lag?
Dodgy EGR valve?
Clutch release bearing as suggested by certed?
EDC as suggested by Richard?
'Flat spot hesitation', therefore software update?

Oh well, ideas to suggest when the car goes back to the dealer.

EDIT

Just spotted these posts on other forums which describe the same symptoms. I am reckoning a new EGR valve is in order...

http://www.focusowners.com/forum/vie...+valve#p323844(last post)

http://www.focusowners.com/forum/vie...t=over+revving
Edited by: mrobbo
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post #9 of 21 Old 12-25-2008, 08:08 AM
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Turbo lag and flat spot hesitation would tend to give no (or Significantly delayed)increase in revs when you pushed the accelerator rather than over rev as you describe it

A sticking EGR valve would also tend to prevent acceleration as it would dilute the air / fuel mix with exhaust so I don't think that is the main problem YET

When it does over rev" doess it feel as though the engine is driving the wheels or does it feel as though the clutch is slipping. As you don't mention it I presume you are not getting a very hot clutch smell





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post #10 of 21 Old 12-25-2008, 08:18 AM Thread Starter
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Hi Richard. The feeling I get is one of the gear not being engaged, anda brief feeling of loss of control over the vehicle. As you suspected, I don't get a hot clutch smell. Hope this helps?!
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