Discovery 2 - auto gearbox - no acceleration on kick down

[Venture4x4]

Hi.  I have a 2003 TD5 D2 with auto gearbox.  102K mile.

Recently bought in good condition.  Went well but a bit sluggish.  Full oil service of engine (plus filters) and gearbox with new gearbox filter recommended ATF used.  Did drive better and change gears more smoothly. Problem:  in 'D' the car goes through the gears OK, I would expect a better response but gets to 60mph OK.  But when I use kick down the engine picks up revs, promptly as expected, but the car does not go any faster (get the feel of a slippiing clutch if manual gearbox) - I do not get the impression of the auto-box dropping a gear and there is no accelleration.  Slightly releasing the accelerator pedal (disengaging kickdown) and the car accelerates.

Performance not stunning and does not compare to my wifes auto Freelander at all.  

Any thoughts?

Edited April 25, 2023 by Venture4x4
mileage wong

[Snagger]

Welcome to the forum.

It sounds like the torque converter isn’t performing properly.  That could be a fault with the converter, the gear box oil pump, a bad seal somewhere or the solenoid valves that control the gear box not operating as they should - all could cause low oil pressure in the torque converter and the excess slip (they do slip by design until a specific rpm in fourth gear).  Unfortunately, I imagine it’d need expert knowledge and equipment to determine the cause.

[elbekko]

How "solid" do the shifts feel? I think that could point to either torque converter or oil pump.
Does it still go into lockup? And if so, does it feel better then? Maybe the "disengaging kickdown" behaviour you describe could point to that - taking your foot out of the throttle could allow the lockup to re-engage.

How did the oil look that came out of the gearbox?

[Escape]

Start with the easiest: is the oil level correct? Remember you need to check cold, with engine running and after cycling through the gears.

[Venture4x4]

Many thanks for the comments.  Oil - the auto gearbox was brown not the nice pink-ish colour of the new ATF.  I presume that it had not been changed recently, if at all.  The engine oil, it was also very dirty looking, but the tell tail was the air-filter very very dirty. So again poor maintenance (last recorded service in the service book at 75K (26K ish ago)).  The oil levels are ok.  Engine easy to check.  Auto gearbox was checked a number of times as per filling recommendations.  

From your discussion and looking at a touque-converter you tube video, I get the impression that the clutch in the converter may be slipping when kick down is applied.  This, I would think, could be the friction material in the converter or the oil pressure engaging it or a combination of both 

[Escape]

Maybe we're looking at the wrong component. From your checks and rereading the original post, it seems the box is shifting OK, just not when full throttle is applied. This could be a stuck wastegate with the ECU cutting fuel when boost rises under full throttle. How does the car behave if you lock the box in say 2nd and then floor it?

[elbekko]

3 hours ago, Venture4x4 said:

Oil - the auto gearbox was brown not the nice pink-ish colour of the new ATF

That may point to the oil having a bunch of water in it. Sadly that can lead to the oil pump burning up pretty quickly (as I sadly found out myself a few years ago). That would certainly cause the torque converter to slip, as there's not enough oil pressure for it to work properly, until the lockup is engaged.