I have read thru many post on several different websites and forums. Have not found my exact issue.
Car rode and drove like a dream.
Bought my 2004 XJ8, put it on the lift at work to install new brake pads. When I put the lift arms under the car I realized the driver front was almost an inch lower then right front.
Noticed the front tires with excessive wear, so I ordered new tires and upper control arms.
The air suspension "Too Low" warning came on a few days later. So I ordered an air compressor. That error popped up twice over a 3 day period.
To install the control arms, had to take the struts loose, that's when I noticed the left front had zero resistance to collapse it vs. the passenger strut was very strong.
Putting on the lift for the tires I noticed the height was the same as it was the first time I put the lift arms underneath.
Installed all of the new parts.
Sat her down, turned the key forward and heard the new compressor run and she lifted up, all 4 corners actually went up quite a bit.
Drove her home. The next day, she was still sitting kind of high, drove to the grocery store. About 3 or 4 miles from the house the front end started feeling funny and the Jag started riding hard and rough.
Get out at the parking lot, looked and the rear was sitting at a normal height, but both front struts apparently let her all the way down where the tires were way up un the fender wells.

Since then, I have checked every fuse and relay. I have let her sit over night with the battery unhooked. When K did that, as soon as I hooked it back up and started the car I heard the compressor quietly engage for a short bit. But the front end never pumped up.
Next I took her for a 30 minute drive including 10 miles of interstate (had rid that it would lower and raise on interstate and back to slower roads)

But none of this helped.

Need to get a front end alignment with the new control arms and tires, but can't do that with her sitting so low.

Any suggestions? My 6th cat, but my 1st 8 cyl,

Any help will be greatly appreciated!

 

You need a scan tool to read the codes from the Air Suspension Module. Troubleshooting without knowing what the module thinks is happening (reading its codes) is pure guesswork.

 

What year is your car? Early (2003 - 2004/5) have two front ride height sensors. From later MY the front is controlled by the one sensor on driver side. The air supply is shared to keep it level. So if one strut leaks air strut both sides drop.
You need to clear the codes to get air compressor back to normal.
Most likely a strut is leaking. That is what slammed it down. From your description it should be the left.
There is a check valve at he top the traps air pressure in strut. If right had pressure and left did not the left strut is the bad one.

 

The only error light or code on the speedo read out is that the Parking Brake has an issue.
The right front was fine and Left was the bad one.
I replaced the left one and it worked for about 12 hours.
I will check the build date. she is a 2004, but not certain if early or late model year.
I'll double check the air fittings... I am guessing this is a model where they share a sensor in front since they both went down together after installing the new strut.

I GREATLY Appreciate the info and suggestions so far, Thanks!!

 

When it was mentioned that the front struts could be tied together, it hit me... Frelmlikensuch an Idiot for not checking thus 1st thing!! .
The new strut, I trimmed the air line and used the new nut on the line.... The line had popped and andncaused both stuts to deflate, I slod it in and they started pumping up and she popped out again... Should have reused the factory one even if it wasn't as shiny as the new one...
Oh well, now I know what to fix... again, THANKS TO ALL!!!

 

Glad it was so simple. Plus easy to access.
You might check RMT for replacements. They stock the caps and olives. Seem to be very good quality, used many times and never an issue.
Check your (olive). It is a hillbilly rig anchor. But works better than it looks.