The ol 2004 xjr is up to about 85k miles now. i baught it at 68k and the mpg seems to have dropped a bit. I used to average 26-27 mpg hwy (even averaged 30mpg from dallas,tx to shreveport, la once@ about 68mph on cruise) its down to no better than 23mpg. I think its probably time for new plugs. Does anyone have any reccomendations for a certain brand of plugs? and any experineces with K&N air filters? i used a K&n on my old 92 camaro and experienced quite a noticeable increase in power "feel"...ofcourse that camaro didnt have a big supercharger so idk if a K&N would make a big improvemnet...what do you think?

 

I have an 04 XJ8 4.2
When I bought it 2 years ago I went through everything and replaced lots of sensors including O2,s also had custom 200 cel cats fitted and performance tune she goes very good it

I also went K&N filter panel and these plugs Brisk Silver Racing Spark Plug | Brisk USA
Been using them in 3 jags now plus my bikes and anything I own with a combustion engine

Very happy with them they rate them at 60,000 k change intervals that plenty long for me

 

I changed my original plugs in my 2005 XJR from NGK iridium to Bosch iridium at 100,000 miles. With the original plugs I was getting around 22 mpg around town and as much as 27-28 mpg on long trips (400 miles). With the Bosch my around town mpg dropped to around 14 mpg. Changed back to the NGK iridium and I am averaging around 19 around town now in cold weather. I use 93 octane from Shell whenever possible.

 

You may know this already however there is a panel in the brake fluid "box" opposite the rear left plug that you need to move in order to get the coil and plug out. If you are going to do them yourself.

 

The factory filter is about as efficient as it gets. An aftermarket unit would be searching for the few crumbs Jag left on the table. Install a K&N if you like the cleanable aspect, not because of a performance boost.

 

Hi Catsgame,

The Original Equipment plugs in our '04 XJR were NGK IFR5N10 Laser Iridium, and I didn't feel any need to second-guess the engine designers. The specified torque for the plugs is 27 Nm/10 lb-ft.

Regarding K&N filters, you might notice a very slight increase in responsiveness (and induction noise), but my personal opinion is that since an air filter that can allow more air flow can also allow more dust and grit to pass into the engine, I'm willing to sacrifice that small performance difference for the sake of longevity for my street cars. For a race car whose engine is rebuilt on a regular basis, I'd want all the air I could get.

If you're really interested in air intake mods, check out caldoofy's very attractive air intake pipe that replaces the stock plastic pipe with all its Helmholtz resonating chambers designed to reduce induction noise:

https://www.jaguarforums.com/forum/s...it-strs-83960/


Cheers,

Don

 

Woah: 60 Million Mile Plugs! The really HAVE improved since I replaced mine last fall. Must get a set of those, LOL!

 

Writing posts on my phone without glasses is difficult at the best of times but as you can see I am from Australia and meant to say 60.000ks intervals on the brisk silver plugs change