As long as ive had my 2001 xj8 ive always noticed this little black plastic knob screwed in under my gas pedal and me being the curious one i unscrewed the knob and took a drive. its like the knob was put there to keep me from reaching a higher gear. im not the biggest car guy obviously but why would this knob be there? Is this doing my engine harm reaching this next gear? With the knob there it seems like its acting as a governor of some kind to keep me from reaching that higher gear. anybody with some insight on this?

 

I assume you mean lower gear.

There are 2 versions of the rubber knob. One has a switch incorporated for the kickdown and the other is just a throttle stop. DO NOT remove it. Even if it is just a throttle stop the adjustment is critical for proper operation of the engine. The WDS has a throttle setup program that outlines and graphs the throttle opening against the stop. If you have messed with the stop you need to take the car to the dealer to have it adjusted properly.

 

What if you bought the car to find the throttle cable was loose? After adjustment, the throttle still has movement after the stop, I have to believe that the software has enough play to make up for the throttle body to be fully expressed.

Not exactly hypothetical, that is what just happened to me. I was searching for something else but found this thread and it intrigued me. I just bought my xj8 and the throttle was very loose to cover up an exhaust leak. I fixed it and re-adjusted the throttle cable and there is still about 15 degrees of movement in the throttle linkage.

I do agree with you that there is a limit, but I would guess that the plastic stop in the floorboard is an idiot-proof safeguard to not overload the ignition software.

 

The gearbox 'kickdown switch' is there to assist in acceleration at full throttle. As stated previousely, it is adjusted with the aid of PDU or WDS while watching the TPS and adjusting it at a certain point for correct transmission operation. If you keep jacking with it you will loose the throttle/gearshift relationship.

bob gauff

 

Sorry for the mis information. I thought I was on the X300 forum and I looked at the 4HP24 and NOT the 5HP24. There is no kickdown for the XJ8 ZF gearbox, It is a throttle stop!!!

My Bad!!

bob gauff