Can anyone help me diagnose this once and for all..

[ySo]

Hi Chaps,

Appreciate any help. Is there anything you think that might be causing the following issue, hopefully something I can sort myself:

My X5 4.4i 2000 plate a good few months back just one day didn't want to change gear if you put the foot right down (engine properly warmed before doing this), it also just revs high and doesn't increase in speed til you let off the gas then it changes gear and acts normal.

**forgot to add a new gearbox was put in last week as it went kaput but the chap used the torque convertor off the old box.

It drives perfectly fine if you don't boot it and gets up to speed just fine, but if you want to put the foot down (ie overtaking) the above happens.

Any ideas at all?

[X5Sport]

Could be a problem with the new box or old torque converter.  Take it back and get it fixed by them.  Changing the box and not the TC is just penny pinching by them.

[ySo]

Would the torque convertor cause that symptoms? The new box defintely works just fine.

I've been googling about and was wondering if the EGR valve could be a cause? As god knows when it was cleaned out last.. ie a very long time ago.

[X5Sport]

If the revs increase but nothing else happens that points at gearbox not changing under high demand.  Could be kick-down switch circuit, incorrect servo operation for the box causing clutch slip, lack of fluid in the box so pressure not enough to allow the hydraulics to operate the gears correctly under certain conditions.

Just how much did they change?  I know the early box doesn't have the same Mechatronics unit as the 6-sp, but is the servo block working correctly?

Have you had a fault code check done as that might throw something up, and not all faults generate a warning light/message.  My gearbox self-destructed (TC failure) and not one warning came on.  Fault diagnostics found it had committed mechanical suicide!