I had parked my 1990 XJS for approximately 6months. I drove it just a few times before deciding to start driving it regularly. The first day I drove the car I noticed it was not shifting out of 1st gear until the rpm was at 6000. I thoughrt at first the transmission fluid was low. Checked and it was fine. The vacuum line was dry rotted so I replaced it. No change. I have also changed out the governor and modular. Still no change. Does anyone know what I need to check or what I am missing? Thank you.

 

Which model do you have?

 

Going out on limb, and based on a few things you mentioned.

I will assume a V12 with the TH400 transmission.

The dry rotted vac line has me strongly suspect the o/ring seal on the pick up spout of the transmission filter.

The trans pan will need to come off, and that filter AND the o/ring replaced.

They do this with age and lack of use, and the trans pump will suck air in lieu of fluid, and the trans will misbehave..

OR

The trans kickdown switch, mounted in the throttle cable AT the capstan, has shorted, and thus holding the innards of the trans in "kick down" mode.

Unplug one of the wires at that switch and try it out.

 

Thank you so much for this information. I will check both of these out. I have been at a total loss on this.

Sincerely
Cindy

 

Unplug the kick down switch. Behind the 2 long throttle arms, a tiny white box with 2 wires, unplug them. It will shift to all gears but will not downshift when you punch the accelerator.
I need a new kick down switch but don't know where to get it.

 

Thank you for the information. I have replaced the kick down switch and still no change. It is a mystery. Working on the other suggestions given.
I was able to find the switch at a transmission shop.

Thanks
Cindy

 

The kickdown solenoid could be jammed in the kickdown position. I have a feeling it cannot be accessed except by a gearbox internal way. It might be worth a) applying 12 volts directly into the switch and listening to hear a click/and or quickly applying 12 v on and off if no click to see if it can unjam; and b) warming up the box and then quickly going from drive to reverse few times to see if that unjams it/and holding the box in 1 on the stick and driving the car flat out, the box will change up to second regardless of the stick position at about 5000 revs. (60 mph).
If it is a jammed solenoid, all these things might unjam it. Worth a try before the box is examined inside.

 

Thanks Cindy, I will find local transmission shop. I assumed it would have to be a Jag part order. Thanks again.
Did you try unplugging both wires ?