Mine doesn't go past 3000/35000. I'm not racing. But it's probably why I'm not getting the 0-60 in 5.3 the X308 is supposed to get. Yes it's in sports mode.

 

The car has a rev limiter if you are in park or neutral, so about 3500 is about right if you are just punching it in park. Mine will shift at about 55-5800 when in gear.

 

If you mean that it won't exceed 3,500 rpm under full throttle acceleration, it is possible that the second fuel pump has failed. This kicks in at 3,500 rpm.

What happens when it gets to 3,500 rpm? Does it shift? Or does it bog down and stop accelerating?

 

I mean when on the freeway. It just stops accelerating. It doesn't die. It just stops accelerating.

 

Definitely sounds like a bad secondary fuel pump.

 

Not sure the exact shift point, but mine hovers around the red line marking on the gauge with wot (wide open throttle) - yours is definitely not working correctly.

 

Yes, afraid so.

 

Yes, afraid so.

 

What about the adjustment of your throttle cable? If it's adjusted wrong and allows to much slack, the butterfly valve of the throttle body will not open for 100%, even if you floor it.
If you got a OBD reader, you can assure that your throttle cable is adjusted right (reading = "100%" if floored for "throttle position sensor"). When idling without touching the pedal the reading should be "8-9%".

 

Here's a TSB concerning the limited throttle opening:

 

You have a point, although seems not in this case, its got all the hallmarks for a pump failure.

On the throttle cable, your info is not correct.
The cable should be tight at the TB, then back-off a 1/4 or 1/2 turn.
After that, the reading of the 'throttle position sensor' should read 90% (not 100%) when the accelerator pedal is pushed against the bump-stop under it.

If not, the bump stop (which is actually a kick-down switch on most, but not all models) can be turned (counter)clockwise to obtain the 90% reading.

Be careful though, if it is a switch, it got tiny wires under the carpet, which will break if you turn the switch.
You will need to peel back the carpet, disconnect the wires, turn to the desired position, and reconnect to check.

 

When I did my road trip last week I went 120 for about 30 seconds in my XJR. It struggled to get up to 120. I figured something had to be wrong. I can't believe a car made to go 150 would have trouble getting up to 120.

 

I just did a road test with a K&N air filter and imy XJR got up to 5000 RPM. I had a Wix air filter earlier. Yes I am being neurotic I admit it. . I had a Wix filter in my 350Z over a year ago and it was the most restrictive performance wise. I ordered an AC Delco paper filter. They were still decent performance wise in my 359Z but I am assuming because they are paper filters they are good at protecting the engine.

 

The idea that the tiny difference between air filters could make the difference between revving to 3500 and to 5000, and between 120mph and 155, is ludicrous - unless the old filter is really, really dirty.

Throwing parts at it will get you nowhere. What you need is diagnostic information. To that end, my suggestion would be to connect up a fuel pressure gauge with a hose long enough to see the gauge from inside the car. That's how I finally diagnosed an intermittent problem with my primary fuel pump - taking it for a drive and observing the pressure.

 

For what it's worth, my '03 had zero issues running to 6k rpm on a dyno (and I did adjust the throttle cable before hand to ensure I had full range). I have to concur to the fuel pump being the likely candidate at that cut off. Unless there's a restricted performance light being tripped but not showing on the dash (unlikely).

 

Just another thought:

A fault in the tranny to ECU communication could make it "think" it is in neutral and not allowing it to go over the 3K limit.

I doubt it is the fuel pump, XJ8's fun fine on one pump, the R only needs it when the boost kicks in, otherwise it is running at normal pressure just like a NA engine.
Vector

 

Vector, xj8's run fine on 1 pump because they only have 1 pump. Xjr has 2 pumps, and it needs 2 pumps. The op must have a fault, he's been told to check fuel pressure which is a good start if he has no codes.
if the ECU thought the tranny was in neutral and he was driving along he would get a gearbox fault.

I would check throttle cable as suggested as it's free. Check air filter. If there's no warning lights then he needs someone to look over it.

 

I had a problem with my XJR with no midrange power. When it hit 3K rpm, it would take off like a rocket.

Turned out the primary pump was weak, delivering enough fuel up to a certain point, but not enough at full demand. The driveability was horrible, but it never turned on a warning light.

 

Yes, I am well aware of the pump arrangement in the 8's and R's.

But, I could be wrong and you may be an "expert" in these matters, who knows?

Vector

 

no expert. Just saying si that the op isn't led down the wrong path.