my 1997 xj6 was due to have spark plugs changed so I went out and got Bosch IR fuzion plugs because I know this car only likes iridium plugs. So when I took the cover off and took the coils out I noticed oil in the spark plug holes. Some more than others but still I knew that wasn't right. The plugs were the original Champion plugs but I assumed these would be better. Now when I drive the car it miss fires under heavy acceleration. Not all the time, but it does do it at random times. I had the valve cover gasket changed about 1 year ago but I do notice oil leaking from the front of the cover (toward ther hood hinge) What could be the problem be with the car? It never did that before the plug change. Any ideas?

 

You have the cylinder 5 and 6 coil connectors in the correct spot, right? The wire with the yellow band is #6.

 

Hi Boeingtravel95,

Ross' suggestion seems like the most likely problem and hopefully it will be that simple. But the oil in the spark plug wells indicates that the plug boss seals are failing and need to be replaced. Were they replaced at the same time as the cam cover gasket?

There has been some discussion recently in another thread about oil in the plug wells causing misfires, either due to contaminants in the oil presenting a lower-resistance path to ground for the voltage from the coil, or the oil insulating the plug ground path to the cylinder head and causing the coil to arc.

What did you do about the oil in the wells before changing the plugs? Did it drain into the cylinders as each plug was removed, or did you suction or wick the oil out before removing the plugs? One possibility is that if the oil in the wells was allowed to drain down through the threaded plug holes, then the oil on the plug threads may be interfering with the ground path to the cylinder head.

No offense intended, but did you check the gaps on the new plugs before installing them?

Also, are you certain that the original Champion RC12YCC plugs were iridium? I thought I recalled that the CC had something to do with extra copper, and the electrode was probably conventional nickel alloy. I don't know if the Bosch plugs have anything to do with your issue, but there has been a lot of debate about whether other brands of plugs are better than Champion. Owners who have used plugs other than Champions have reported mixed results. Bryan N of the Jag-Lovers forum once did an 11,000 mile comparison of OE Champion RC9YC plugs with the NGK equivalent in his XJ40:

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Nothing against NGKs - they are the correct OE plugs for X308s and X350s, as well as our BMW, but where Jaguar recommended Champions, the empirical data may suggest that it's prudent to use them.

Cheers,

Don

 

Jaguar or any other company doesn't recommend any one plug because of any exhaustive research that shows they work better then another, more then likely a business partnership and $$ decision. I'v been running NGK Iridium plugs in my 97 for four years, no problems what so ever.

 

JT- You are probably right in general, but there are a number of posters on this and another forums who have reported success getting the idle to their satisfaction only with the specific plug Don recommended. So, maybe there is some subtle difference? Or- Even if it is all in their head, don't blow it for them!

 

People are under the impression only "copper" will work, all NGK plugs are "copper core" no plug can use copper as an electrode as it will have a very short life span exposed to the combustion process.

http://www.ngksparkplugs.com/pdf/dyk_5points.pdf

 

I'd pull the coils and see if the wells are full of oil, if so you need to stop that and make sure the coils are not trying to fire through that. The oil will capillary wick up the inside of the boot and make the coils work harder/hotter which will result in fouled coils.

 

I'm sure you're correct that Jaguar did not exhaustively test lots of spark plugs and choose the Champion over all the rest. But I'm equally confident that they designed and exhaustively tested the AJ16 engine using Champion plugs, which may be far more significant.

As far as I know, from at least as far back as the original XK engine that W.M. Heynes began designing shortly after WWII, Jaguar specified Champion plugs. The Champion brand goes all the way back to 1908 (the company was renamed AC in 1909), so Champion plugs were standard on many, many brands of motor vehicles.

Whether Jaguar's relationship with Champion was based strictly on marketing, economies of scale (bulk purchasing power), the convenience for dealers to stock only one brand of plug and for Jaguar to specifiy only one gap range, or the simple fact that in those days spark plug options were limited, Jaguar engines were probably exclusively designed and developed using Champion plugs until the introduction of the AJ-V8 and its Denso engine management system, at which time Jaguar switched to NGK plugs, which were no doubt the ones Denso used in developing and exhaustively testing their EMS.

Whether brands other than Champion will perform better in an AJ16 I can't say, but there are enough variables in plug design to say with certainty that not all plugs will perform equally well. See this document from NGK that spells out many of the design and performance considerations:

http://www.ngksparkplugs.com/docs/te...plications.pdf

Regarding electrode material, one thing to note if you use a more modern plug is that the resistivity/conductivity of Platinum and Iridium differ from that of conventional nickel alloys, so the manufacturer may recommend a gap that differs from the one specified by Jaguar for the original Champion plug.

So one way of looking at this issue is to ask, "Is it better to use the plug used in the design and testing of the engine, or to use a plug designed for aftermarket use in a lot of different engines...?"

Cheers,

Don

 

If anyone thinks Champions of today are made anywhere near the way they were in years past they are sadly mistaken. Run what you like. I used to take my Bonneville and start it cold and watch it lump around on idle with champions in it, let it warm up and it was no better, change out to a set of NGK B7ES and BAM smooth, perfect idle. Not a "today's" Champion fan by any stretch and if you want my honest opinion I feel they make a perfectly good fishing weight. I run NGK Iridium in my TR-6, XJS V-12 and my X-300, never had a hic-cup one on any of them. I think people who have had issues with other plugs and then corrected with ole school Champions fixed a connection or got the gap or coil connection right on change out. Through personal experience I really don't think it was the plugs fault but something corrected in the swap out. Not here to start a "plug war" just giving my observations. Most guys I knew in Brit Bike circles wouldn't run modern Champions....at least not for long!

 

No one should ever set a plug gap to the cars specs but to the plug manufactures spec for that car. My TR-6 gap is different then that specified by Triumph for their recommended plug vs the iridium. I can also "extend" the gap while running the electronic ignition vice the points.

 

I can't understand why so many folks think today's Champion plugs are somehow not as good as they were in the past. If anything, given advancements in materials technology and manufacturing processes and the pressures of global competition, they're probably better than ever. For many years Champion was an independent Fortune 500 company but is now owned by Federal-Mogul, one of the largest automotive OEMs that supplies original equipment parts to automakers around the world.

If Champion plugs appear as original equipment to a lesser degree than in the past, I would argue that it has less to do with any decline in Champion quality and more to do with some of these factors: Champion's ability to remain independent for so long as automakers established their own plug factories, the ascendancy of Asian automakers, and the asendancy of engine management systems made by companies that either make their own plugs or have longstanding relationships with plug makers other than Champion. Think of these EMS makers/automakers and their plug associations: Bosch (Bosch), Denso (Denso/NGK), GM (GM/Delphi/AC Delco (the AC stands for Albert Champion, by the way)), Hitachi (Hitachi), Ford (Ford/Autolite/Motorcraft), Chrysler (Champion/Mopar), Honda (Denso/NGK) and Toyota (Denso/NGK).

Chrysler, Hyundai and Kia are still factory-installing Champion plugs in some of their engines, and it is likely that some of the automaker-branded plugs are actually made by Champion. Champions are also run in a lot of racing cars and boats.

In the mid-2000s, Ford had problems with two-piece Motorcraft plugs that carboned up and siezed. Once the Motorcraft plugs were removed (with great difficulty), most mechanics installed a superior one-piece plug made by Champion...

In this day and age when plug makers need to be able to offer plugs for as many aftermarket applications as possible, it is even likely that some NGK, Bosch, Motorcraft and AC Delco plugs are made by Champion, and vice versa.

For the record, in the '90s I bought into the marketing hype for pricey Bosch four-electrode platinums and tried them in our '88. I could discern no improvement in the way the engine ran, and if anything, it seemed as though it didn't want to rev quite as freely in the upper rpms. On the next plug change I went back to plain old Champions and all was well again. For the past 17 years, Champions are the only plug I've used in our '93, and I've never had a single plug-related issue. The current set is just a few years old and works just as well as the sets I bought in the '90s.

I have no association with Champion and I'm certainly not claiming there isn't a plug by another maker that will work better in either the AJ6 or AJ16. But just because the Champions are older tech and less expensive doesn't mean they won't work perfectly well, if not better, than most other plugs, given that they were the plugs the Jaguar engineers used when developing and tuning the engines.

Apologies to Boeingtravel95 for the digression in his thread!

Cheers,

Don

 

Well said Don B.

It's my understanding that the switch to platinum plugs from copper was primarily due to demand for less maintenance, not specifically because they were "better" plugs. Now modern iridium/unobtainium plugs with pinpoint electrodes are a different matter. With how cramped modern engine bays are it's a very good idea to have very long life plugs. But our X300's are about as easy a plug change as you could ask for, short of a lawn mower perhaps.

I'm sticking with Champions.

 

FTR, over the course of years and 130k miles I used both Champs and NGKs in my X300/XJR. Never noticed any difference in behavior whatsoever.

As to misfire problems.....

FWIW......

I had more than my share of misfire episodes with the XJR, almost always down to faulty coils (I could write a book). I did do battle with a mystery misfire, though, that had me pulling my hair for 2-3 months. Ross might remember my trials and tribulations.

The gruesome details are not important at this point. But, on pure whimsy (or was it misery-driven desperation?) I tried a new set of plugs. Naturally I had inspected the plugs early on and, being only a few months old, I didn't expect to see a problem and wasn't disappointed. However, a new set of plugs totally cured the problem. There was some sort of invisible fault....or perhaps just the fiddle factor at play.

Cheers
DD

 

Doug. You are a "Sage" I had that problem some time back and followed your advice and fixed the problem. As for the oil problem the seals need to be replaced before replacing the ignition coils.
Thanks again Doug

 

Hi Boeing, Take a close look at your plugs again. A hairline crack in the porcelain nose will cause the arc to track to earth before it jumps the plug gap.

 

Hi Take a look at this TSB from Jaguar re: Spark Plugs

http://www.jagrepair.com/images/TSB/...6%20Engine.pdf

 

Thanks! Nothing like a little documentation!

 

And TSB at the link below shows that the new, hotter plug mentioned in the TSB BigBossRadio linked to, part number EBC 8143, is, in fact...

Champion RC12YCC

http://www.jagrepair.com/images/TSB/...rivability.pdf