I have noticed a very consistent and distracting characteristic of my XK8's transmission and wondered if anyone else has experienced anything similar?
First, my entire valve pack was completely rebuilt a couple of years ago and fluids are fresh as well. There was a significant thread I made on my transmission woes but happy to say that since I found the actual issue with my transmission, the car has been pretty much bulletproof ever since - except for this one thing.

So, over the last couple of months, I have been having fun building my own exhaust system for the car. It has been a great learning experience and although I do not consider it finished just yet, I am pretty happy with the results so far. I will be making a separate post on all of that once I am completely finished with the project. I think you will all find it very entertaining. Since I did this in stages, there were times when the engine was pretty loud and as I built the various bits going backwards, the car got progressively quieter. When it was loud, it amplified an issue I have noticed for almost the entirety of my ownership and now that I could clearly hear - as well as feel - the issue, I wanted to investigate further - starting with the past experiences of others. Even more obvious as I have been driving using the J-Gate shifter more routinely - which I absolutely love BTW.

The issue is most prominent in 3rd gear, but I think it does it in 4th as well but nothing in 1st, 2nd, 5th and 6th.
The issue is not throttle dependent and happens whether I have my foot into the throttle or not.
The issue us that as the car climbs through RPM's through the gears, it gets to third, begins to rise normally and then - for lack of a better term - hangs in the RPM range before finally climbing to the shift point. Sometimes it feels like the RPM's actually drop off a little before a recovery to the climb. I know the first instinct is that this sounds like worn clutch components, but it does it like this even with only the slightest amount of throttle and believe me, I have put serious boots to this car over my ownership and it makes no difference in this effect. If I had worn clutch packs, I would suspect that by now, 3rd and 4th gear would have completely disappeared on me. No debris in the fluid when I changed it either.

Since my car is a 2003 - first year of many things on the subsequent years, I am wondering if this may have been some sort of tech bulletin that required an ECM update to resolve? To my knowledge, this ECM has never seen any factory updates to the firmware and I always wondered what they fixed in the ECM over the years of the 6-speed auto?
Anyone else out there experience anything similar that makes you scratch your head?
Outside of that - everything else is working nominally

Looking forward to hearing the experiences on this issue. Not even a big concern but it would be cool to learn if this is a common issue and has a resolution?

 

You may want to consider having the ZF 6HP26 Transmission Adaptations Drive Cycle procedure performed on your car (assuming you can find a Jaguar-familiar shop that still has the hardware / software / experienced technicians to successfully achieve it). Google the Technical Service Bulletin JTB00145 to read all about it. This procedure immediately resolved the rough shift issues my wife complained about in July 2013. When she complained the same rough shifts had returned in April 2016, having the procedure performed a second time immediately resolved the issues once again....

 

To my knowledge, this is why folks mention "powertrain". The transmission and engine are working together as a system. When you speed up and go through the gears, the ECU backs the throttle a bit to ease the wear on the transmission clutches and make the transition smoother. This is of course only possible with drive-by-wire instead of a direct pedal-to-throttle cable.

Before applying Jon's advice, you could do the $0 reset of the throttle sensor. Start by adjusting the slack in the cable (check the "bin" where the brake booster is), then, key on, engine off, slowly press the gas pedal to the floor (all the way, including the WOT switch if there is one) and then release several times in a row. It is supposed to teach the ECU the real range of values the sensor can actually produce, and adjust the opening of the throttle plate accordingly. This can be monitored over OBDII (throttle %, etc.). Some report seeing 100% throttle only after these adjustments have been made (free power and all that). Hopefully, this procedure will help. Or not and then you can do the re-set of the adaptations as Jon describes.

Best of luck, keep us posted.

 

Thanks to you both.
I have the JLR software and had previously reset adaptations numerous times when working on other issues
I was also privy to the throttle position and adjusted my cables to achieve 100% opening - done through visual in the JLR software.
That's not to say that over time - and various things changing with the cars age etc. that a new reset won't be beneficial so I will go ahead and do the reset and let the forum know if I notice a difference.
Thanks again for applying some knowledge

 

If you have SDD, you could try your hand at graphing some of the many data points available over CAN. Engine RPM, vehicle speed, maybe torque or even clutch slippage. You might see dips in these graphs to confirm your experience.

 

I don't know if my "problem" is the same as yours but sometimes when I gently accelerate the car will keep the revs a bit higher when it could change up. It will change up eventually though just seems to not want to change up so quickly. I think this is just because I am going up hill and I am in sport mode. But it gets to about 3000rpm and then changes up. It's stuff like this that makes me wish Jaguar had a manual option for these cars. Much more simple. Mine is also a 2003 model. I am wandering if I reset the adaptations it might help as it has likely never been done. I have heard that if you hold the two battery leads together for 20 seconds it resets the adaptations, is this true?

 

Holding the two disconnected battery leads together is called a hard reset and is known to resolve some electrical issues in these cars, but unfortunately that will not accomplish the ZF transmission adaptations procedure as described in the TSB....

 

While we are checking things, don't forget to have a look at fuel trims. Trims higher than, say, 5% have a noticeable effect on throttle response. Codes only trigger at 25%, so there is a big range where drivability is impacted, but no codes show up. Remember, trims are a function of load and rpm, so you need to capture the trims as the conditions you describe are happening. I am sure SDD can do that, but the record function in Torque Pro is probably the quickest way to check on this (eyes on the road and all that). Would not hurt to record fuel pressure either. FWIW, the air flow meter for our later XK8s seem to be on the cheaper end, so throwing in a new one is an option.

If you have more time, record individual wheel speed during these test to eliminate the possibility of a loose ABS reluctor ring. Driver rear seem to be "special" to determine road speed.

Best of luck, keep us posted.