After driving for the past week I've noticed the tachometer creeps at highway rpm. At 70mph it will start about 2400, 20-30 mins later it's slightly above 2500. Maybe 2550, 2600 with no change in speed.
Is this normal? After reading about the coolant gauge being an idiot light this makes me wonder how reliable the tach actually is.

This leads me to another question. What is your rpm at 70? 2400 seems high to me coming from my corvette which pulled about 17-1800 at 70.

Thanks!

 

Is that in fifth gear and non-sport mode?

It might be that your torque converter is slipping once the transmission fluid is hot.

70mph would be somewhere south of 2200 rpm.

 

I didn't get any books with the car. Just to confirm normal mode (non-sport) is button pressed in red light out? This is how I normally drive. At speed the button doesn't affect RPM but when stopped the button definitely works. I can hear and feel a slight change in gears.

Carfax indicates the car was serviced regularly. There is no easy way to check the tranny fluid that I can see. Is there?

 

Sadly no, if you look in the HOW-TO's at the top of this section you'll find this

https://www.jaguarforums.com/forum/x...-cd-faq-54942/

I know (without perfect pitch) it's hard to say but do you think the revs are actually creeping up or the gauge is wrong?
I can't find a wiring diagram for the gauge but guess it is driven by the main cluster from CAN signals from the ECM.

 

No I'm not sure. To my ears the RPM doesn't seem to have changed. What I read about the coolant gauge not being a true gauge made me question the reliability (truthiness? truthability? LOL) of the tach.
It seems like the older Jags use VDO?

 

The engine temperature gauge is deliberately spoofed to stop owners panicking when it strays off the middle position. Not a good idea but there you go.
The tacho, though, should be spot on.

 

Correct. The tach is a stepper motor gauge driven by speed data from the ECM. Unlike the coolant gauge, it should be accurate.

I suggest getting an inexexpensive OBDII reader with real time data monitoring capability (search 'ELM327' on ebay for units under $20) and use it to independently monitor the RPMs. Download and install the free software in the attachment to this message if you get the PC version, or download the app 'Torque' if you get the bluetooth version for an Android phone. You will then quickly see if the gauge itself is a problem or not.

 

You can rely on the 'other' Steve to come up with a simple solution.

 

Ok, thanks guys. Will do!

 

FYI, a 1999 XJR would have Mercedes built W5A580 transmission and not the ZF transmission. It is a much better transmission.

The fluid level on a W5A580 can be checked in the normal manner with a dipstick, although the dipstick is not supplied and must be purchased in the aftermarket.

Red light on = sport mode on, and the drivers handbook is available as a download, likely linked in the FAQ's for this section.

 

OK, I commandeered a small OBD2 scanner and have a P1797
I found on this site JagRepair.com - Jaguar Repair Information Resource Seems like P1797 will set limp home mode? I don't have that though. Other than seemingly high rpm it seems fine. How to trouble shoot CAN/ECM corrupt messages?