My 99 XJ8 Sport is very reluctant when it comes to kick-downs.
When flooring it right from the start the car is very fast.
But when driving at any speed and then flooring it there seldom is a kickdown (downshift).

That behaviour almost got me in trouble when I passed a truck last week on a small two-laned road.
I was lucky enough and got past the truck right before the opposing traffic.
But that incident made me think...
What's wrong with the kickdown in my car?

That might be a very dumb question, but on my 99 XJ there is no kickdown switch underneath the pedal.
Just a black plastic pedal stop knob.
Shouldn't there be a switch?
Do I have another problem or is that the way the Jags behave?

Your input is very much appreciated!

David

 

David, give it a push with your hand and a straight arm, it should click on and off. If it doesn't it might need adjustment or replacing. The "stop knob" should be the actual switch.

 

Sean,

it definitely is just a piece of plastic!

I had removed it for closer inspection a while ago.

No switch, no cables, no electronics in it.
Just a plastic pedal stop knob, really!!!

+ I couldn't find any cables near that place where a switch could have been plugged in.

Strange, isn't it?



P.S.
Non-supercharged 4.0 V8 AJ27 engine, MY 1999

 

The kick-down switch has 2 parts, the upper black plastic knob and the bottom part which is the electrical switch.
To adjust it correctly you need an OBD2 reader that display throttle opening %
Push on the gas pedal until it make light contact with the knob ( light meaning that the switch do no "click"
In this position throttle opening should be 90%
If not screw the knob in if the reading was less than 90% and unscrew it if the reading was more than 90%

 

PUT THE SWITCH IN SPORT MODE!!!!!!

Check the throttle cable adjustment.

bob gauff

 

Okay, there is obviously something not right...

I have an OBD-II reader.
WOT was about 83% (if I remember correctly).
(With no pressure on the pedal it still was 4% or so. Cable had slack though.)
I checked the pedal stop (that was when I found out that there is NO switch) and screwed the "stop knob" fully in.
WOT now was about 89%.
I adjusted the throttle cable until the OBD read 99% @ WOT.
So far so good... Test drive ...
After engine warmed up I got a high idle (around 1500rpms).
So I adjusted the cable again (a few revolutions back) until idle was fine again.
WOT (per OBD-reading) now: 92%.
I'm not able to get more throttle opening per adjusting the cable. That will only increase the idle rpms.
And my "idle" throttle opening is around 4-5 percent (throttle cable completely released)!
Idle RPMs are around 600.

Another problem which is possibly somehow connected with the pedal/switch/throttle-cable problem...

I have the newer style throttle body with no vacuum unit on top.
Sean wrote that probably my ECU is mapped for the older style throttle body.

I appreciate any thoughts!

David

P.S.
I'm heading for the garage to take a picture of my no kickdown-switch-stop-knob...
Will post picture...

 

Pictures...

 

Interesting- My XJ8 doesn't have that knob but does have the screw sticking out. That normally stops the pedal but if I push it hard it slips over that and boy does that car go like a scalded cat!! I reckon you check this thread out though David: https://www.jaguarforums.com/forum/s...t=38663&page=3
Go to page 3 for our engines.

I did this job on mine and it made the difference, and the kick down was a little more responsive. I know you say you adjusted it already but there are many Qs & As related to the adjustment.

Hope This Helps!
S.

 

Okay, interesting. So your car has no kickdown switch as well.
How does it behave when you floor it (in "normal" not in S-mode).
Does it downshift?

 

After tightening the accelerator cable the car is more responsive in normal and will downshift normally i.e. if I slow for a corner or come to a hill. If I floor it, it moves, and I mean moves fast.

As I mentioned earlier if I push the pedal right down (so it pops over the screw sticking out) it goes fast. I don't floor the car often these days (Can't afford to with these fuel prices) and certainly don't push it past the screw as I figured out that that stop is there for a reason.

There probably is a kick down switch somewhere but it is most likely hidden in the throttle body or somewhere in the pedal box.

 

The ZF 5HP24 gearbox DOES NOT use a kick down switch. The Mercedes W5A580 DOES use a kick down switch.

The 2000 to 2002 XKR used the W5A580 trans.

bob gauff

 

Thank you Bob for that clarification!

So it's true - everyday you learn something new.

 

Interesting info... thanks.

 

I get a strange effect from my kick down, a really bad delay, and almost like a stall, the car bogs down, there is a second or so of a delay, then it drops a gear and takes off. anybody else had this?

 

I would venture its not the switch that is the source of that problem, but more likely throttle body and/or air/fuel delivery inconsistency or even spark. Lots of places to get into, but a good tuneup with new plugs (maybe even ignition coils), air flow sensor and throttle body cleaning, new air filter, fuel filter, vacuum leak investigation and correction, fuel additive to clean the injectors, etc.

 

Thanks, that sounds like a good weekends work.