Does anyone know when you actually need to change the spark plugs? What is the tailtell signs when they should be changed?
I now have 97K miles on my car and did an oil change today. I couldnt find a single oil leak, drip, weep or anything wrong. I have never had a light come on the dash except for the parking brake fault (which I work on and off for about 5 minutes and it finally sends the fault away for long periods of time). I just wonder if I need to change the plugs at this point. The car isnt as smooth as it once was but runs smooth once totally warmed up. Im used to my V12 and W-12 engines so a V8 just wont ever be as smooth. Anyway, I was thinking about changing my plugs on my 07 XJR. Is it a hard job and what does it entail? Please advise what I should do, leave it alone until I get a poor running car or is the slight idle at start up a sign of needing to replace the plugs? Please advise.

 

Hi Collector1,

According to the Service Schedule at the link below, the spark plugs in a V8 should be changed no later than 100K miles:

2006 MY Vehicle Maintenance Checklist (miles) : JagDocs, The Source for Jaguar Documentation!

I personally would recommend using the original equipment NGK plugs to ensure proper performance, operating temperature and operating life. For our '04 XJR the OE plugs were NGK IFR5N10 Laser Iridiums.

Replacing the plugs is relatively easy with the exception of the #8 cylinder, where the clearance is tight. The plastic coil covers can be carefully pried out until the snaps release, then you have to carefully work them up past the oil dipstick tube and other obstructions.

The coils are each affixed with a single hex-head screw (8mm?). Take care when disconnecting the coils' electrical connectors since the connectors and wiring insulation harden and become brittle over time. Once the connector is free, just twist the coil as you pull it up off the plug.

To remove the spark plugs use a standard spark plug socket (I think it's a 5/8 in. size), an extension about 10 or 12 inches long, and a 3/8 in. ratchet. It can help to turn the plug very slightly clockwise to break any corrosion, then reverse the ratchet to twist the plug out counter-clockwise.

For the #8 cylinder, which is the rear right cylinder when facing the front of the engine, pulling the coil out will require some twisting and contorting and a little rubbing on the box that surrounds the brake master cylinder. To remove the plug, add a flexible joint or "universal joint" between the socket and extension and use an extension long enough to get your ratchet above the brake master cylinder box for better clearance while twisting the plug out.

Cheers,

Don

 

So, if I wanted to do it myself, how hard would it be? Do I have to replace the boots like most Fords? What does entail?

 

Same engine as some other jag models and there's a post with pics somewhere but it's not very hard if you have the various tools already mentioned. (Don't even start if not.)

 

There is a plastic door/cover in the side of the brake reservoir compartment, on my 2005 XJR, that allows you to go thru that compartment to get at the spark plug more easily.

 

I was disappointed to learn that our '04 XJR doesn't have that access door, but it wasn't too difficult to get at cylinder #8 with a flex joint.

 

Before changing them have a look at (long term) fuel trims in case you've some data to help you see something else may need doing. Hot engine, at idle then rev to about 2500. (You can always look again after changing.)

 

Quote by Don B "I personally would recommend using the original equipment NGK plugs to ensure proper performance, operating temperature and operating life. For our '04 XJR the OE plugs were NGK IFR5N10 Laser Iridiums."

I made the mistake of using plugs that Autozone recommended which were not the original. My fuel consumption worsened significantly. So I changed my plugs twice in a week. I now have the originals as Don B stated.