www.jec.org.uk

I,m changing spark plugs on my 96 celebration 4.0 AJ16.
Current plug fitted is as specified by manual Champion RC9YCC.
David Marks confirmed he uses these as service replacements.

However - on Jag lovers forum (mostly USA imputs) it said this plug has been superceded by RC12YCC - a hotter plug.
I have not seen any instruction confirming this. Has anyone?
Also has anyone used the equivalent new IRIDIUM type plug offered by most leading brands , if so what heat range and did it make any improvements?

appreciate any comments

Brian 696
96 Celebration 4.0

Hi Brian,

I have some rough running problems on my 1996 XJR. This was made worse (I think) when I switched from RC9YCC to the colder BKR7E. I have got some NGK BKR5E which are equivalent to the Champion RC12's, so I shall let you know what difference it makes.

To be honest, unless you're experiencing some rough running, I would stick with the RC9's.

Regards, Jonathan.

update on AJ16 4.0 spark plugs

Fitted Bosch FR78X super4 plugs bought at Halfords for £2.28 each.

Confirmed as suitable by champion & bosch x/reference charts.
Did 1200 miles around UK over 18 days.
450 motorway miles on outward trip returned 30.2mpg at average speed of 70.4mph.
Overall mpg for full trip was 24.7mpg including ten days in Cornwall (all hills and rain)
Generally happy with new plugs and no problems running. No adjustment required and expected life is 36K miles.
Sounds good to me

BC
4.0 celebration

Brian,

Good to hear your views on the plugs.

As a matter of interest, was that 30.2 mpg a genuine figure based on tank brim to brim actual fuel used or was it a figure from a trip computer?

Paul

hi paul
MPG figure came from trip computor - not an actual fuel bought/used calculation.
However, generally I felt the figure was reasonably accurate against what I spent on fuel.

BC