When I first bought the car it had a check engine light on saying something about the 3-4 shift having problems so I assumed one of the solenoids was bad but the car wasn't slipping but the rpms never really went higher than 2000 even at 90mph. Anyway so after almost a yr of driving I had the restricted performance light come on a few times so decided to change oil and might as well put new solenoids in while I was at it. Long story short replaced solenoids with some I found on Amazon and changed oil. Now the transmission is slipping when I accelerate fast if I go slow it's fine and the solenoid 3-4 code is gone. Does the transmission have to adapt first or is it the fluid is to high or low? Any ideas?

 

Definitely try to drive it around a bunch relatively gently and don't use sport mode. I don't have a definitive mileage number, but try to be gentle with it for around 500-1000 miles, then see if you still get slippage.

When I had the transmission in my S-Type R (same 6HP26 as in the XJ) swapped with a good used one, the mechatronics assembly was swapped over from my old one. The adaptations from the old mechantronics pack were all out of whack and giving the Jag any hard throttle would result in a massive amount of slip and a transmission fault, even with brand-new fluid in a known good low-mileage transmission.

I put about 500 miles on the car, doing gentle in town driving as well as 70 mph highway cruises, all never in sport mode and never any throttle application past 50%, and the transmission gradiually adapted and now it's been doing hard, solid pulls for nearly 10k miles since the swap!

Definitely drive your car gently, but miles and gentle treatment with plenty of opportunities for shifting sequentially through all 6 gears should give the mechatronics unit the chance to properly learn your transmission.

 

Probably the best thing to do is a CLEAR ADAPTATIONS and reconfigure TCM. (mechatronics)

Unfortunately it requires dealer level diagnostics equipment.

 

amazon solenoids are a no-go, solenoids weren't your problem in the first place.

3-4 shift is always a trans out job to fix, no amount of line pressure is going to fix a stator support that can't seal

 

Did you have your adaptions reset or did it just adapt on its own?

 

What's wrong with the Amazon solenoids?

 

Frankly, read what xalty wrote. He's spot on.

 

The shop who I had do the transmission swap had the adaptations cleared.

The transmission should adapt on it's own after some driving even without resetting adaptations, it may just take longer than if you did. Getting the adaptations back to where they need to be with new solenoids should at least give you a mostly drivable Jag again and buy you some time to explore your options for rebuilding or replacement if the 3-4 shift is still giving you issues.

 

After replacing the transmission fluid and cleaning off my old solenoids the 3-4shift code was gone but a new code came up saying that the torque converter solenoid was stuck closed so I went ahead and replaced all the solenoids with the ones I bought from an auto parts store online who obviously bought them from Amazon and had them shipped to my house. So now all the original codes are gone but I have a new code now showing P1605 (temporary) TRANSMISSION CONTROL MODULE CHECKSUM FAILURE not sure what or why any help would be appreciated.

 

In my case, clearing adaptations makes the gearbox shift very very hard. To make it very smooth again, you have to use the gearbox adaptation cycle (where you must drive exactly like SDD tells you).
Just waiting for the gearbox to adapt on its own, doesn't work.
As the gearbox adaptations sometimes drift over time, I had to re run the cycle every 5 years in average.
As result, you will not even notice the gearbox shifting.