kickdown operation

how is this operated on the p38 is it electronic or what and how does it operate

don't you just slam yr foot on the accelerator? i don't recomend it cos it sounds expensive on a 4 litre!!!

Usually kick down is a step on the throttle pot cam. as the throttle cam turns to around 85% open there is a ridge on the cam, this is what you can feel pop under your foot as you push it down, as the ridge is higher than the rest of the cam, it ups the pressure to the maze of valves, and makes the box think it needs to change up a gear.

kushti!

but does it recieve it signal from the throttle switch which then sends signal to ecu? or similiar?

the kick down is nothing to do with the ecu or throttle, its all to do with the automatic gearbox, the more the throttle is turned, the more pressure is applied to a certain part of the gearbox, up until 85% throttle when the "kickdown" gives it a pressure boost. This upping of pressure in that particular part of the autobox system signals to the box to change ratios.

The whole throttle cam bit is just a gauge/sender really to tell the autobox what to do.

right i see as my car keeps kicking down on 1/3rd throttle, it drops in, then out and back in and out.

changed everything on it now, so im guessing its possibly box related or as u said above can u give me some more details on this matey as u seem to know ur stuff.

is there anything i can strip down and clean before i got balls out on a new box

sorry to clarify it doesnt do it 25% throttle but does it between 35% - 50% throttle the kick down just cuts in and out until it changes gear then does it all again, its alright if i drive everywhere flat out

also, mine is a p38 incase we get confused here

Just to cover my own arse, I'm a motorsport engineering "student" Having just finished a unit on autoboxes, hence why i'm able to talk about them (Ask me in a few weeks I won't have a clue :lol: ) But anyway, that sounds like a fluids problem to me, as if one of the seals may have gone inisde the box, bit of a problem because the hydraulics in an autobox are insane, I'm quite happy to strip down and play with manual gearboxes all day long, but I'd bloody think twice about an autobox. I'd be tempted to get a couple more opinions from people in here, and maybe take to have it checked out.

But I think it's a seal gone inside the box.

and you're definately in D and not 2 or L

yeah definately matey!!! lol

does the stepper motor and MAF sensor need setting up on the p38 as this has been on and off many times now and could have been disturbed, heres the clue to this as it has only done this since i left the plug off for the throttle posistion switch one day and took it for a test drive (or was it the idle control valve, cant rememeber)

ive changed. plugs, leads, coil , 2 lambda, 8 plugs, 2 new cats, tps sensor, maf sensor, fuel rail sensor, and gearbox ecu

jesus christ!! that's a lot of new bits!! Well like I say I'm not 100% ofay with the p38's workings, not having one to look at! but I guess first port of call may be to make sure that switch/sensor you've unplugged and rejigged is connecting/working properly, if you can, check that the voltage is changing properly from the throttle sensor at varying throttle states, and not jumping, which could send a bad signal.

Maf sensor don't need adjusting it just sends a direct signal of how much air is flowing / second.

checked the throttle posistion switch as u said, also belled out all wiring for continuity and also to make sure its getting a reading back to ecu, now uve mentioned that its pressure controlled im gonna look for air leaks maybe take the manifold off again and reseal.

is there a vacuum pipe then that will run to the gearbox?

may go along the line of a new manifold in case mine has hairline crack i cant see also, seems strange it has only happend since i left idle control off, or maybe just coincidence

It's all internal hydraulics, no pipes or anything, all fluids and the seals are internal, if you cut the end off one on a lathe it looks like one of those maze things you have to roll a ball bearing around in! Proper labyrinth. So short of having it looked at by a specialist I'm not too sure what to suggest.

I'm sure there will be someone on here before too long that knows a bit more about them than me.. have some more/better ideas!

cheers for your input matey

Theres a useful drawing in the handbook showing at what pedal positon kickdown ciomes in.you sure you aint got a heavy foot?You'll chew yer diffs and gearbox using the kickdown a lot.And kickdown changes down a gear not up!

im hundred percent certain if dont move the throttle at all just keep it in the same place and it just drops in and out of kickdown

anyone else like to advise please