V6 Kick-down

When I use the kick-down on my V6 Freelander, depending how far I press the pedal depends how many gears it drops down. If I don't floor it it seems to go down 1 gear and accelerates fine, changing up smoothly and on going. If I floor it of it goes again dropping 2(?) gears but when it changes up revs drop dramatically and it stops accelerating, ease of the throttle and it carries on.

Any ideas?

Tempus Fugit said:

When I use the kick-down on my V6 Freelander, depending how far I press the pedal depends how many gears it drops down. If I don't floor it it seems to go down 1 gear and accelerates fine, changing up smoothly and on going. If I floor it of it goes again dropping 2(?) gears but when it changes up revs drop dramatically and it stops accelerating, ease of the throttle and it carries on.

Any ideas?

Click to expand...

Normal I'm afraid. The Transmission Control Module (TCM) isn't that smart, it's simply following a set of pre-load rules. As you say, you get a two stage kickdown. First stage, giving you a single gear drop and a bit more power. The second stage is designed to give the maximum amount of power available. Bear in mind that the KV6 makes full power at the rev limiter of 6500 Rpm. The box TCM deliberately selects a gear to allow the engine to run up to this high Rpm, providing maximum acceleration. It could drop any number or gears to do this. There is a slight glitche in that the TCM doesn't appear to know what gear is the lowest, therefore pointless gear, until it's actually changed. This can give you a strange effect of dropping to a lower gear than needed, only for the box to change up again almost immediately. Generally at this point, the driver hears the engine race and backs off the throttle, at this the box shifts up. However it appears that the TCM is already planning the next up change so it changes up two gears instead of one. This can leave the engine out of the torque band, forcing another down change. I hope that makes sense? There are some things that the TCM simply can't account for. In a manual vehicle, the driver can see in advance what is ahead so knows what gear is needed long before its selected. An auto box is blind to everything except the drivers foot position and the road speed. Everything else is a guess to the TCM.

Surly it would know the lowest gear possible for current speed from it's own known limits of speeds for each gear. It could just catch say 2nd gear 5mph lower then the max for this gear, then change up to third with the engine much higher up the rev band as opposed to dropping straight to 3rd and not being able to rev near the rev limit straight away in 3rd.

The only time I get what you could suspect to be an incorrect change is accelerating fast (not kick down) and backing off near a gear change. Matching the revs for this would be down to it's reaction speed to cancel a change request.

Thanks for the reply, at least something I can live with and not worry.

Ta.

Take control and use in the step tronic mode and see if you get on better, always found mine better on steep hills if I held the gears manually.

Nodge68 said:

An auto box is blind to everything except the drivers foot position and the road speed. Everything else is a guess to the TCM.

Click to expand...

I am not so sure about that...obviously it senses engine revs too. And I suspect it also understands a bit about load ...

Anyway the way to drive an auto box is to left foot brake so that you get retardation and right foot accelerate so you get shiftdown.

freelance said:

Take control and use in the step tronic mode and see if you get on better, always found mine better on steep hills if I held the gears manually.

Click to expand...

Will give that a try. Ta.