I have had the car eight months after defecting to MB for a few years. Now back in UK for reirement bought 2003 4.2 V8 probably the best engine Jaguar has ever made.Having had eight other XJs over the years since 1974 Series 1 drives just like my C5 Corvette when it was on Eagle run flats and worse than when I put Avon tyres on it. Really that hard. All I get is I think its a bit hard but not too bad. I changed all four tyres to Bridgestone P6 cos they were the quetest tyre here in the UK no better. Anyone any suggestions.

 

Look up some prior posts regarding suspension height (measured from centre of wheel hub to wheel arch) and check yours.
Sounds like your air suspension( if it hasn't been replaced with a coil over system) is probably in an error state and maxed out at full height.

If however your car has had aftermarket coil over suspension fitted, then you might be investigating what type has been installed and explore alternative options.

 

I see you previously had an X350 XJ6, and some basic air suspension knowledge.

I wonder if the air springs/dampers were changed at some stage and possibly with the Sport ones (Red Dot) instead of Comfort (Green Dot). Unfortunately the dots are hard to see with the units in place, and there's not always much choice in current spares offerings.

I would describe my X358 XJ6 as "harsh, harsher" after the air springs were replaced (with OEM).

 

I have been reading this forum for many years and over that time there have been
similar complaints from owners.
Often they will; say "I am not sure if it is real or not" etc. and usually it was real.
I suggest therefore that you do a search on this forum also using Google for
info re your problem.
Others will correct me if I am wrong but if your suspension is hard that means that
5 volts is applied to some or all solenoids at the top of the struts.
I recently had the idea of switching that off by pulling out the connectors on the top
and then DRIVING it !
I suggested this to one owner but never got a reply!
If you try this idea please post results

 

According to Don's summary from the sticky's, no signal is “firm”, “soft” is 5 volt 400Hz PWM (which is not just 5v).

I'm not sure how this relates to "Sport" or "Comfort" air springs.

 

It should be the same for both versions. The only difference between "Sport" and "Comfort" is the air volume of the air bladder:


Best regards,
Thomas

 

From the ECATS summary, the setting is always "firm" below ~25mph (40kph). Therefore if the OP (or me) considers the ride harsh below this speed (and I do) then ECATS is not a factor.
OTOH, Comfort or Sport air springs is always true. Although I have no idea what difference to expect.

There's really no way to tell when ECATS "kicks in", in my blissfull ignorance.

 

What I do not understand is why Jag wanted a harsh ride below 25MPH!

 

To shake The Queen awake when She arrived at a Do?