My 86 XJS V12 with 50k miles is running rough. Usually i change out spark plugs when a car is running rough, cause it's easy. However, I'm learning that nothing is easy with a Jag. What does it take to change the plugs and plug wires?

Thx

 

Opinions/advice will vary. Here's mine:

Remove the cap and wires entirely. Remove cruise control bellows. Remove the throttle pedestal. Remove the 4 compressor mounting bolts to it can be tipped upward.

Now you can reach all of the plugs and can blow out (or vacuum out) all the garbage that falls into the spark plug holes when you take them out....and the extra room means less chance of cross-threading the new ones.

It'll take an afternoon. Don't rush. The car will fight you.

Cheers
DD

PS-if you have the time, money, and enthusiasm, go ahead a replace fuel hoses, cap/rotor/wires, and make up a new injector harness while you're at it. Might as well set the throttle blades, replace the plastic throttle bushings and synchronize the linkage, too. IOW, do it all at once and be done with it. You'll be set for years.

 

He had to ask about the difficulty of plug changing, I think all those other things are WAY out of his league.... One wonders why they buy a car like this then....

 

Anyone who is an experienced veteran was once an uncertain first-timer. A V12 Jag does make the learning curve pretty steep, though.

Cheers
DD

 

Hey Ukat - consider keeping your smart *** comments to yourself. I quick look at your posts shows you are much more likely to make negative remarks then provide any helpful info (with the exception of the trans drum post).

You could learn something from Doug, his comments are helpful and informative, which is what these forums are all about.

 

Just spotted this. I too, pretty much learn something from Doug every time he takes the trouble to answer a question.

Keep up good work Doug we all appreciate it.

 

I appreciate the nice comments, guys.

Many many years ago I was a nervous first-time Jag owner with NO answers and MANY questions. I try to remember that.

Cheers
DD

 

I found this a couple of yrs ago when I did mine,it was helpful for a rookie Jag owner.Hope it works I'm stupid with this computer(and other )stuff
Les 88 1/2XJ-S
file:///C:/Documents%20and%20Setting...0the%20Vee.htm

 

Hey sacrider if it doesn't work you can google "accessing the vee" and you will find it
Les

 

Hey Les, you have posted a link to your hard-drive, and....that....don't.... work.

If you want to share the file, send me a PM and maybe we can get together to get it into the FAQ.

Cheers,

 

We all have to start learning somewhere. With me it was motorcycles in the days when their reliability could not be taken for granted, (Yes,they were British bikes !!). Then I got into cars and straightaway it was a Jaguar XK engine in a Mark 2 I had to attend to. A pretty steep learning curve there !! However, a V12 - whow, if you learn on these everything else will seem easy-peasy.

 

Thanks NoSox - looks like a good article. Here's a link to the article:
http://neptune.spacebears.com/cars/stories/vee.html

I've got to put the spark plug project on hold for the moment, first I need to track down a coolant leak. See my separate post for that.

 

I was forced to do exactly what Doug said when I discovered a large rat's nest on top of the distributor cap.
In addition to removing all the fecal material and rat urine, I decided to do all the plugs, wires, cap and rotor. It was a real PITA, but a great learning experience nonetheless. I am not a mechanic, but the V12 makes everything else seem like a walk in the park. This is the reason why Jag mechanics are so expensive...

BTW, I read Kirby's fix on the flawed Marelli rotor and will be going back in there soon. Good luck to you!

 

bought new plugs the other week for mine, glad I came across this. great information here. going to try the Bosch Platinum +4, has anyone tried them,

 

its not that bad, the worst in my opinion is removing the throttle tower.

Be sure to gap all of those plugs and keep the valley clean!

 

After reading these posts, I had to ask. My dealership stated that I had non spec plugs on my XK8's engine. I asked them to return those they found installed when they were replaced but haven't seen them yet. Can anyone tell me what this is all about? What's unique about the spark plugs in my car? Any harm done or what issues come about with these non specs installed?

 

You might want to stick with the OEM standard. I know my AJ6 does not like anything other than the standard RC9YC. YMMV

Cheers,

Allan

 

Stick with the plugs the ignition system was designed around. The high priced iridium plugs installed by the previous owner on my 4.0 AJ16 caused misfires and check engine light to come on. I pulled the plugs, went back to the $2.00 champions, and have not had a misfire since.

 

IMHO, on a V12....considering the amount of labor involved.....I'd be reluctant to experiment and whould go with whatever choice stands the highest chance of success and least chance of problems. In other words, as specified by Jaguar

On the old straight-6 Jags, where you can replace a set of plugs in 15 minutes and whistle while doing so, it isn't too painful if an experiment doesn't pan out.

That said.....

Over the years I've never noticed an iota of difference by experimenting with different brands of plugs. Until, that is, a few months ago....and even that's a bit uncertain.

I have used both standard-grade Champions and NGK Iridiums in my XJR with good results. I did do battle with a misfire mystery (long long frustrating story) where the fix was replacing a set of Champions (only a few months old and appearing to be in perfect condition) with a set of NGKs.

(Or was it the other way around? gah....I've confused myself now!)

Anyhow, the mystery misfire went away. Whether it was truly an issue with the *brand* of spark plug or some other fluke, I can't really say.


Cheers
DD

 

I agree with the recommendation of using the regular spark plugs. The fancier ones do not work well with this engine, and as was posted, may lead to misfires because the engine is expecting one thing, and it's being given another. The best thing you can often do to keep it running good is stick with original specification parts. Often, not always.

On a scale of 1 to 10, with 1 being easy and 10 being most difficult, I'd say that changing the spark plugs is about a 3, maybe a 4. The first time you do it, it is going to feel frustrating, especially if you are used to American or Japanese cars where the spark plugs are often right there available for easy access. Take your time, understand how and why things were assembled the way they were, realize that most of this car was assembled by hand, and you'll see that the next time you do it, it might only take you an hour or so.

If I may also add to Doug's instructions. If you should find yourself changing the rotor and distributor cap (and I think you should, you're there already), make sure you give your distributor some lubrication. A few drops of oil in the center hole of the rotor shaft should suffice, if it's not stuck. The rotor shaft should move freely about 10 degrees counter-clockwise, and then SPRING back to position. If not, you may have some additional work on the distributor.

And in case you're wondering what a 10 difficulty job might be, I'd say it's probably changing the timing chain tensioner or crankshaft seal. Maybe the sump gasket?