V6 CDTI loss of power on downchange

[m8internet]

This has happened twice now, can't really understand how or why...

Cruise control set at 50mph, and in 6th gear
Approaching a slower moving vehicle, so plan on downchanging to 5th gear, pass the slower vehicle, then back to 6th gear and back on with the cruise control

However, on downchanging from 6th to 5th gear, the revs just increase and increase and increase, and no change in speed
So I go for 4th gear, and the revs do exactly the same, right up to 4500rpm
I therefore dip the clutch and allow the engine to come back to 800rpm, and go back to 6th gear and reestablish 50mph (having come down to about 45mph)
I then boot the throttle and everything is back to normal

Both times has been on a right hand bend

Any and all ideas or questions welcome

[_ZS_]

New clutch time.

[Penfold101]

Nothing like breaking it to him gently lol

[Duncan]

Does sound like the clutch. Just to check do this test on a straight road (to rule out the fact that it was due to going around a right corner). Drive along and select a gear that would be a couple of gears higher than you'd normally want to be in e.g 5th in at 30mph for example. Accelerate so that the car would be under a bit more load than normal and see what happens. If the revs rise like they did before then it's looking very much like a new clutch.

[wardy]

sounds to me like the cut off (cruise control not disengaging) when the clutch is pressed, so the car is still trying to maintain same speed.

Wouldn't that indicate a cruise issue rather than clutch issue??

[wardy]

If you think it is a cruise control issue, just ever so slightly dab the break (just enough to disengage the cruise) before selecting the lower gear. If that works Ok then I would think its the clutch pedal not disengaging the cruise.

Still a problem, but hopefully a cheaper one.

[m8internet]

The clutch itself is fine
As per roadtest, I tested that on completing the journey

Sounds like it might be the switch on the clutch pedal...
However, for any change in speed and gear change I always use the "off" switch on the Cruise Control and takeover full control of the vehicle
That still doesn't explain why the revs increase but not the speed
Normally epxect when coming down one gear and applying power to get at least some oomph, but nothing
There is just no change in speed and/or drive at all
My next thought was Traction Control, but it doesn't flash or come on at any time either

If it happens again, book the car in for some "free" attention

[wardy]

The car won't go any faster (unless you hit the throttle) as the cruise is still on, if I am correct.

The cruise is trying to keep the car at a constant speed. The more you change down the more it will rev, but still won't go any faster.

[wardy]

Didn't think there is an "off" on the cruise.

On mine the top button engages the cruise, and subsequent presses will increase the speed. The bottom button on each press (once the cruise is on) will decrease the speed, and does nothing when the cruise is off.
the only "off" button is the clutch & break pedals.

[m8internet]

If the cruise control is on, lets say at 50mph

If you press the gas peddle, the car accelerates, and if you remove the gas peddle the car returns back to its original pre-set speed, however if you increase your speed by more than about 30mph the cruise control switches off

There are three buttons for the cruise control
The lower one is for reset speed (and lower speed)
The upper one is for resume speed
The large one behind them is the cancel button

I've got another longtrip tomorrow, so can test again
The first time the problem occured was about three weeks ago, the second time was on Monday
If it was the clutch, then I would have thought it would affected many more journeys and "traditional" driving and gear changes, along with hill starts and so on, but it is only as described above
Also, the VX dealership is on the way home, pass in and ask if they have ever heard of this problem (hint, I can kind of guess what the answer to that is!)