Last year I purchased my 2005 Jaguar XJR. It was purchased with 78,000 Miles but now has 80,000 Miles. (130,000kms).

I have had many Jags and currently have 4! But this one is very confusing. I got a professional device and its pulling 0-60mph the same as my dads 2004 XJ8. I have a measuring device!

My wife also has the 05 Super V8 and it's a lot faster. same engine and hers has done 140k Miles.

Well, I took it the my Jaguar Mechanic, he couldn't find a issue with a quick hour diagnosis. Absolutely no check engine lights. Runs smooth. But just lacking about 100hp!

He did a software update and it didnt fix anything. Very annoyed.

It was the same before I also modded. Not I done Mina Gallery Exhaust, Pulley, Intake but has made no difference. Still with those mods its 7-8 seconds to 60. Same as my dads XJ8!

I Dont know what to do. I am wondering is there a air leak? I'm not sure but has anyone had this issue?
Thanks for all your help!

 

Assumed the engine is mechanically (compression, valve clearance, timing, kats) and electrically (fuel pressure, ignition coils, spark plugs, etc.) OK, there may be a problem with the boost pressure or boost pressure control.

First of all, the boost pressure should be checked while driving. The ECU gets the boost pressure information from the MAP sensor, which can be read out. Additionally the boost pressure information of the MAP should be checked with a monometer. Depending on the results you have to investigate further. It may be that the boost pressure is not built up by the compressor, that it escapes through a leak or is incorrectly regulated.

Fritz

 

Thanks Fritz

 

If it were me, I think I would begin with a compression check.

 

Does that car have two fuel pumps (as per mine)? If so, maybe one isn't working right...

Another thing could be IAT2 (or the SC pump) - car will lack power if it signals too much heat in the SC cooling circuit (or pump doesn't work).

 

Choked catalytic convertors?

 

OBDll will flag low power issues. Suggest you have it scanned with JLR reader and post codes here

- What type of gas mileage are you seeing; normal driving? (and, assume you're using 93 RON)
- Later (X356, X358) SC cars are quicker, if you're comparing
- As noted, make sure your SC radiator and pump are clean and operational; air filter element fresh
- Check also for dragging caliper (this will show up in gas mileage as well)

 

Thanks everyone I will talk to my mechanic. This is a great forum.

Currently no codes. I do have a Autel $1500 code reader.

Thanks Karl

 

Not familiar with Autel, but make sure it has JLR package. Look for secondary codes (and, X350's generally have 'em)

Using reader, you should be able to ascertain boost pressure with live data (and view as graph in historical). Test it both fresh and after sitting idling for 10 minutes; post here

Ditto; log fuel pressure. Have you replaced the fuel filter?

Also, suggest do your acceleration comparisons with ~ 10 mph rolling start; DSC off

 

I had something similar on mine. No codes, revved OK but just didn't fly like an x350 XJR should.

Eventually it wouldn't rev over 4k, and made a weird almost rattle sound coming from somewhere near the supercharger. As a last ditch attempt to avoid refurbing the blower, we took a gamble on it being excess backpressure, ran it on open headers, and discovered the problem. The cats themselves looked OK but had obviously become clogged over the years (it had a few years of doing very low mileage before I bought it).

We put in 200cel sports cats and the car absolutely flies now...

 

Thanks for everyone's help! I got some checking to do.