Hi everyone,

When I am driving and I put my foot down, it doesn't drop into a lower gear and take off. It does accelerate quite quickly mind you, just not with that awesome overdrive thing kicking in.

Now, when I have cruise control engaged and I press the Set/+ button and hold it, it does drop down into a lower gear and take off like a shot.

I've also noticed the throttle pedal is a bit stiff to operate.

Is any of this familiar to any of you? Is there some adjustment I can make or does it sound like a more serious problem?

Thanks,

Pete.

 

There's a throttle cable adjustment procedure somewhere in the files or x308 forum, your cable could be corroded/gummed up inside causing the stiff pedal feel, there is also a kickdown button under the pedal which gets depressed when flooring it which should send a signal for the trans to shift down ASAP if possible.

 

Nilanium,

I never noticed anything under the throttle before. I just had a look. There is a flattened, threaded object sticking out from the floorboard, but no switch. I'm gonna go and take a picture of it and post it. Gimme 5 minutes...lol.

 

so, does this look normal?

 

I just looked on the Jag parts database. I found the kickdown switch. Whaddya know? It is missing from my Jaaaaagggg.

This will not do at all!

Thanks Nilanium.

Pete.

 

Maybe not, the earlier XJ8's were delivered with a stop, not a switch.
From your picture it looks to me you are missing the stop, its not the switch.
I might be wrong here though, you can check if there is a connector hidden under the carpet.

 

Hey Eric,

What's not the switch? The threaded post? Does your VDP have a switch?

I don't understand. What is the purpose of the "stop"? Did this stop mount on the threaded post that currently exists? If a kickdown switch was not provided in the earlier XJ8's, how did the kickdown function get activated? Did it get activated at all?

I checked the travel of the throttle pedal. It does not go down as far as the threaded post. There is a gap of about 3/4". Also, I pulled the carpet away to look for a connector. There isn't one. Roughly where was the connector located? Perhaps I was looking in the wrong place.

On the parts database, there is a kickdown switch, PN: LJC6570AA, listed for my VIN, from VIN 853936. Also, the parts database does list a "Switch mounting stud" I presume the mounting stud provides the negative terminal of the switch. The wire coming from the switch must connect to the wiring harness somewhere. Activating (closing) the switch must ground a 12V signal line to activate the kickdown. If not for the fact that the switch needs to be adjusted and must engage only at the correct moment, any momentary switch could provide the function; even one mounted on the steering wheel.

Now, even though the switch is listed on the parts database, they are just not available anywhere any longer. Maybe in some junk yard, somewhere...

Anyone got one to sell to me?

 

Sorry, I was a bit in a hurry in the last post.

What you see is the threaded stud, which is used for adjustment (will get back to that).

On that stud, there is either the kick down switch (with 2 wires), or just a stop (without wires).

There is some confusion on which model years / models have the stop, and which the switch.
I have tried to find this info myself, but even Jaguar instruction manuals are not clear on this.

My guess is 1998 XJ8 models, maybe into 1999 XJ8 models as well.
An other theory might be that the AJ26 engine had the stop, the later AJ27 had the switch.
On the XJR I am even less sure, maybe the same, maybe those were supplied with switches from the beginning.
Again, mostly speculation from my side.
One thing I know for sure though, my 1998 XJ8 VDP has the stop, and does the kick-down as it is supposed to do.

You will have to pull the carpet up around the stud, if you pull it from under the center consul, you can create some leeway, but it remains tight.
The switch has a relative short wire, but of course that cable could be anywhere by now.
Maybe someone with a switch knows where it comes from, I guess from the pedal are but I am not sure.

Then on the adjustment:
The common advice is to adjust the cable at the throttle body, but that is only half of the story.
You actually will first need to give the cable a certain amount of slack.
Then you will need to adjust that stop / switch in such way (turning in or out on the stud), that the TB valve opens 90 percent while the accelerator pedal just touches the stop / switch.
You can check this with any OBD2 software like Torque Pro.
There are some other conditions while doing this, like a cold engine, there is a Jaguar instruction sheet, I will look that up and post later.

So in your case, it might very well be that your cable is far too tight, hence the gap while fully pushed.

 

This is an extract from the manual, it is for the XJR with a switch, but I used the same procedure for my XJ8 with a stop.

Jaguar Workshop Manuals > XJR (X308) V8-4.0L SC (AJ26) (1998) > Transmission and Drivetrain > Automatic Transmission/Transaxle > Downshift Switch, A/T > Component Information > Adjustments

So first set the cable free play at the TB,
Then measure the TB valve opening with OBD2 software,
Aim for 90% when pushed against the stop / switch.
I did all with a cold engine.

Note: If you will need to use the switch, disconnect the connector every time you need to turn it to adjust.
The wires are very fragile.

 

To me, this sounds like your throttle cable needs to be adjusted. You do this from on the throttle body (under the hood, near the windshield in the middle), your butterfly valve should fully open when you floor the pedal (with battery on, but engine off!!!)

 

This is not correct, the TB valve setting is 90% with cold engine.

 

@Imanonamas - pop the hood and reset your throttle cable, then see if it kicks down. Your car could have the stop, not the switch and this is the fastest way to find out. Also, if there isn't a loom tucked away, then it's likely it's a stop your missing, not a switch.

If the throttle pedal travel can be monitored with OBDII scanner then the job is easy. I set mine as close to the 100% and got a restricted performance, so the Jaguar setup is the correct way.

 

I set mine by eye (without checking obdii) when I got the car 6 years ago and tried for 100% open, been driving fine like that ever since.

 

If you did it on a cold engine, then the valve will not open more than ~90 degree anyway (Remember, the valve is operated by a stepper motor, the cable is not directly connected to the valve).
That's probably why you set it right.
Just be sure there is a fraction of play on the cable, too tight is also not good.

 

Hi guys,

Thanks for the replies. I shall adjust the cable in a few days when I have some time off. Interestingly, I floored it this afternoon while driving home. It did kickdown into a lower gear. I pushed the pedal down as hard as I could. I do think it might be the cable tightness.

Just to clarify, the purpose of the switch is just to make kickdown occur earlier. Right?

I'll keep you all updated.

Thanks again.

 

If equipped, it's to put the car into wot mode (wide open throttle) that basically tells the computer to utilize 100 maximum performance in the engine + transmission.

It should trigger at the end of pedal travel, so not any earlier.

 

Doesmthat count for the older TBs as well? Coz mine hass motor, cable and vacume box...

 

In my case, AJ26 engine, 4L, yes, no more than 92% on the readout (cold).

 

AJ26 here too... So okay. Means you have the vacume pot too (the black little cylinder on top)

 

Yes.