In my 2003 XJR it seems it does not go 0-60 in the 5.3 seconds I see listed for 0-60 time. The supercharger doesn't seem to kick in until I am going 30 MPH. When going up hills or when I am on the freeway I definitely feel it. I have a 2004 Nissan 350Z that is listed as 0-60 in 5.6 seconds and the 350Z feels faster than the XJR. I just put a new Wix air filter in the XJR as well as changed the transmission fluid and put BG44K fuel injector cleaner in the tank. Any thoughts?

 

Is there a sport mode button?

 

I get the same symptom a lot of the time. The problem is traction. Flooring it from the lights results in wheel spin, and the ECU cuts the power in response. Do you see the traction control light flashing on the dash?

You might need better tires. What are they?

 

The reason I asked about sport mode is the XKR will not start in 1st gear unless the sport mode is on. I'm not sure if the XJR is the same.

 

Yes, the XJR is the same.

 

Yes. I always leave it in sport mode.

 

As it's a mechanical device, if it's working, it should be working all the time, and if it's not, it wouldn't be. Doesn't mean it might not be working but poorly, if there are seals or such gone awry. You could pull the belt off and test to see if it feels any different, that would at least give an indication that there might be something wrong with it. You should certainly feel it get up and go from a standstill if you hit the gas, well before you get to 30.

 

Also listen for the intercooler pump in the right front under the filter with the ignition on, and see if the the heat exchangers feel cool.

 

Couple of things, the supercharger "works" anytime the engine spins, period. However it does have a "bypass" which could get hung up allowing some of the boost to not be used. Normally if it was something that adverse you'd get a "restricted performance" light. I'd do a proper cleaning on the MAF sensor, check that the bypass is able to open and close properly and see if there are any pending codes. Turn the key to "run" and squeeze the hose coming off the intercooler pump to make sure You feel flow. The car will also build more power on cooler days as opposed to warmer days or less after continuous hard runs.

 

Light throttle and not very steep ... do you hear pinging?

Exactly what used to happened to me just before both fuel
pumps bit the dust. It must have been running on one
pump while the other was already dead.

 

I would expect a Nissan 350Z to feel faster than the Jag, on account of the dreadful road and engine noise, harsh ride, and uncomfortable seats.

 

It was the Throttle Body. The original one was no longer working. I had a rebuilt one installed and it drives like a totally different car now. Now I know what 370 HP feels like.