I've got a couple of weeks left on my warranty and thought I would get some opinions from the group. At constant throttle, steady grade and steady speed, the RPMs seem to move slightly up and down with a frequency of about one complete cycle per second. Same thing happens with cruise control. This happens often in 6th (top) gear on a slight grade. I would have assumed that the torque converter would be locked and therefore there would be no "slip" or hunting at constant road speed.

Another weird thing is that at constant speed, if I give the car a little gas to accelerate, the revs instantly rise as the car accelerates, the same way any non-locked torque converter would do. *However*, less than a second later the revs drop about 100RPM as if the torque converter was locking up (Why wasn't it locked up already at steady cruise?). The car continues to accelerate smoothly the whole time. If it weren't for my opened up exhaust, my ears would never have clued into the strange behavior.

The 6HP26 tranny is supposed to be able to lockup the torque converter in all gears, but from the above two examples it doesn't seem to lockup at all or it seems to glide in and out of lockup according to some algorithm that I can't figure out. Any thoughts? FYI -- my tranny seems quite normal in every measurable sense -- good fuel economy, no CELs, good full-throttle shifting (same as another XJR I drove a while back), good smoothness, etc.

Thanks,
Mike
'04 XJR

Mike

 

Modern gearboxes like yours do have torque converter locks to save the last 100th of a gram of fuel on cruise, but they are controlled by the electronics so can switch in and out as the box controller thinks necessary.
From what you say about 6th gear and going up hill, the box controller is switching out the lock to maintain speed instead of changing a gear. From the other things you say, all seems OK. You could try a fluid change too.

 

Good point, but the hill/grade I'm talking about is very, very mild. There's no way the engine was anywhere close to having to struggle to maintain vehicle speed. I've driven the same road in cars with 1/3rd the horsepower and the torque converter stays 100% locked and the RPMs are as steady as a rock. In fact, of the dozens of rental cars that I drive, once you get the tranny into top gear, you can feel the converter lock. Once it locks, road speed and engine RPM are move together with none of the yo-yo that my XJR experiences, even on slight hills.

I'm probably paranoid. But in my defense, expiring warranties do that to people.

Mike

 

Does it do this all the time, or only when cold?

 

It does it all the time. It's a good question. Automatics don't usually lockup the torque converter unless the tranny fluid is warm enough. In my case it doesn't seem to matter.

Mike

 

The 04 is known for the torque converter. I would take it to a dealership ASAP to get it documented so they have more time to fix it. I have the same issue. When my car is cold it doesn't happen, but it also doesn't shift into 6 at lower speeds (50mph). Once the car reaches operating temp it starts and ussually stop about 15 mins after that in the cold. Curious it it will be the same in warmer weather. It also feels like it's the same pedal position. If I lightly press the pedal more it will stop or release the pedal it will stop.

 

Yep, the TC is a possible problem, but the TCM can be given a coded re-flash at a dealer, which is supposed to deal with the problem. If it's this issue, when warm it shouldn't do it.

 

I have read that the 2004 XJ's have torque converter problems - what about the 2006's? Same X350 platform, sounds like the same transmission. Just want to know what I can expect from my car's transmission.

John

 

I have only read about it on 04 in this forum. The possible cause that I have heard of are TC, Flushing the Trans and TCM reflash. If I had a warranty,I would try and get all three done. I'm going to try everything besides the TC and use the ZF moddifier since I do get the noise between shifts.

 

Take a look at this thread. It may give you some help.

https://www.jaguarforums.com/forum/s...ad.php?t=23158

The dealer I use was stumped; and refashed the TCM three times before I provided him with info that I got from other members here. The torque converter was the issue.

GET IT DOCUMENTED!!!

 

So its new torque converter time, maybe.

I am really surprised a company like ZF can let things like this through; selling their products to car manufacturers is their bread and butter, and I would certainly not want to get a bad reputation if I was their managing director.

 

You folks were right. The dealer says that I need a software upgrade... for $140!!! It's not critical that I get it. Still, a software bug to me is a manufacturing defect that should be fixed for free. I confirmed with Jaguar Canada that the software upgrade is not covered under the Select warranty, only the base 4yr warranty.

Thanks again to all that chimed in.

Mike

 

A very modern torque converter clutch has a "modulated" action; some of the time it will be going in and out, driven by the operating program. It is intended to do this to...
Save some gasolene/diesel.
Reduce torsional vibrations.
In over-run to keep the engine revolving while fuel over-run shut-off is in operation.

I don't personally agree with this idea, but it's designed that way. End of...

Leedsman.

 

You're right. This behaviour is described in -- of all places -- the owners manual. I didn't find any mention of it in the service manual or anywhere else. Slipping the lockup clutch seems pointless.

Mike