re: 2004 XJ8 It feels like a lean condition while in cruse mode only, usually
in high gear between 1800 - 2200 rpm
It has a very definite surging to it, it doesn't do it while accelerating hard
up through the gears or if you just hit a lower gear while in a passing
situation.
The car runs great otherwise, the car has 86K miles.
Is there a part that needs replacing at this mileage or is the computer
programed from the factory this way for emissions and fuel economy ?
The fuel economy is excellent and cars runs great, what gives ??
Thanks for any input ..

 

Sounds not quite right. Maybe watch fuel trims via OBD and see what they do.

 

torque converter locking and unlocking?
it's been a known issue with this transmission.

You can search this forum, there are some useful threads.

 

Rosskuhns,
I just had the trans rebuilt, and am very confident with who did it but I
am new to the XJ8 world so maybe this could be the case even after a
rebuild.
It just really feels like the motor is leaning out, is normal to get 26-28 mpg
highway.
Jag V8 (above) said ( Maybe watch fuel trims via OBD and see what they do)
Is that done on a chassis dyno or in the shop, parked with motor running hooked
up to a laptop or a Jag diagnostic machine ?
Thanks ..

 

Was the TC new or rebuilt or did they do anything to it?

The TC clutch lining is a well known failure and your decription matches it very well. Generally this failure will not set an error code.
.
.
.

 

tbird6,
Good question, I just looked at the invoice for the trans rebuild, all it said
was replace trans.
I will call the shop and ask them.
I also did a search on this forum and found a ton of posts with the same issue.
The most informative was this one by (oldmots)
(Working on the engine to solve the cold surging will not help, it is the TCM and/or the torque converter. There is a CODED reflash for the TCM that the dealer can install. It has to be coded from Jaguar to the dealer before it will download. If this reflash does not work, the TC replacement is the only fix. This appears to only affect ZF 6hp26 in the 03 XK range and the 04 XJ range. The XK got the 4.2 and 6 speed 1 year before the XJ and it is the 1st year models that have the problem)
I will report back after learn more ..
Thanks

 

Update --
Trans did get new rebuilt converter, so I'm going to schedule a "re-flash"
I'll let you know how it works out ..

 

good, that is exactly the thread that I was thinking about!

 

OH HAPPY DAY ! The gremlins have left, the transmission is now in perfect
running condition.
I got the computer reflash/update done on Thursday, the shop that did the recent
trans rebuild was able to handle the computer update too.
They hooked up the cars computer to the Jag factory headquarters
and started the update, they found old problems and fixed them, they
said the car was 2 update's behind ??
I guess that means we need to periodically ck with Jag to see if there are
any new update we could take advantage of ..
The new reflash fixed the problem with the torque convertor locking up at
the wrong times. ($130)
The tech guy said it wasn't a patch that they did, the master Jag computer
can communicate directly with the trans program and give it a whole new
trans program & they did the same with the motor, since they are interactive.
Thanks to russkuhns for steering me in the right direction
Later,
Joe