2003 XJR ( x308)

After reading a zillion posts on spark plugs I realized that the posts are even more opinionated than the answers on the what oil to use threads. Also many of the posts are 9 or 10 years old and as we know technology changes with time. So keeping it simple...............
1, Anyone know what the original plugs that came new with the car were ?
2. I'm going to use Iridium plugs... choice is between Denso or NKG.....any experience with either ? ( leaning toward NKG BKR6EGP or Denso IQ 20TT..comments ?
3, the discussions on gap are endless.....again what is the correct gap.

The car ( near mint) has 44000 miles on it and has become "grumpy" when starting cold ( misfires).. Once warm it runs like the rocket ship that it has always been.
Jaguar TSB recommends plug replacement on a SC car at 60k miles so I;m getting closer to plug change time anyway.

All replies appreciated

 

The correct spark plug for the X308 supercharged is C2A1535, which is an NGK Iridium design. The original spark plugs had part number AJ84575.

The cross reference NGK part number is IFR5N10 and should come pre-gapped at .040 inches.

 

Many thanks !!!!! You cut right through the BS , Guys like you are what makes this site so valuable ,,Thanks again

 

FYI: The reason you see all the BS is because people don't want to buy the direct part and pay $13 a plug ... even more for Jaguar retail. They buy cross reference -- or the NGK plug and battle over the gap size. The correct part is ready to go.

Also -- some engines just run better with the plug design made at the time of production. Newer is not always better.

Both of my 02's have original plugs. 42K and 75k ... runs fine ... that's not to say you don't have a problem with yours. Make sure to check in all the wells and go over the coils for any oil or moisture.

 

This is the X308 spark plug "evolution" extracted from the NGK (UK) website (NGK Partfinder for Cars & Light Commercial Vehicles). The extensions "13E" and "11E" mean preset gaps of 1.3 mm and 1.1 mm respectively. For the last spark plug in the table, the "10" at the end means 1.0 mm gap.

 

So you can see the confusion !

The gap changed over time -- as did the heat range. When you add in the other cars with simular engines .. everybody is always saying. Why pay X when I can get "Y" for much less.


Nice to have them all together MS

 

See post #5 for Jag gap specs throughout the x308 years https://www.jaguarforums.com/forum/x...8/#post1773939

Think I got NGK Iridiums, came out of the box at .04 and I carefully gapped them to .05 inch. Seems to work fine as far as I can tell... Forget what my old ones measured out to.

 

post #2 tells all you need to know for SC

 

Post #2 has it for me, too.

Great plugs. Be very very gentle with the centre electrode. Meant to be sharp, for good reason.

 

Agree .. that's why I tell everybody to get the correct number in post #2 and you don't have to play with them ... if you order the NGK cross number the gap is different.

 

ok I have some NGK IFR5N10 plugs in my 2002 xjr and getting fouled plugs on 1 and 4. got on several sites including ebay and pulled up NGK IFR5N10 and they claim these plugs are
not compatible with my car...any comments or what is the correct answer?
also these plugs only have about 25-30k on them what is the best way to clean them, I have a sand blaster, would that be too aggressive?

 

I just into plugs as well today and couldnt find a confirmation on the NGK IFR5N10. Doesnt mean they couldnt work, but I didnt see why to buy them.
Instead I ordered the NGK IFR6E11.

link to NGK part finder
https://ngksparkplugs.com/en/part-finder

link to Autozone part finder
https://www.autozone.com/external-engine/spark-plug

I am not an expert on cleaning spark plugs. I would replace if they werent working properly, even if it is just after 30K. Especially if you are not sure you have the right plugs to begin with. But as said....not an expert

 

The AJ26 SC uses PFR6G-13E plugs and AJ27 SC (year 2000 on) uses PFR5G-11E plugs. IFR5N10 is same as PFR5G, except that it has iridium electrodes for longer life, so it is also a correct plug for AJ27.

The actual change to the spark plugs between AJ26 and AJ27 was their heat rating. PFR5 (or IFR5) are somewhat "hotter" than the PFR6 of AJ26. Hotter plugs have higher resistance to fouling as they more efficiently burn-off any combustion residue on their electrodes. So, the heat range (that controls the fouling) of the plugs has already been increased on AJ27 by the factory to what is required (suitable) and should not be the reason for the fouling of plugs 1 and 4 on your engine. I would check the compression to see if it is perhaps lower on these cylinders. If the compression is good, I would replace the 1 & 4 ignition coils.

As for the cleaning, sand blasting may damage the ceramic insulators. It is sufficient just to wash them with some solvent and wire brush the electrodes.

 

Hi powellwm,

Did you notice any oil in the spark plug wells of cylinders 1 and 4 or on the spark plug threads? Leaking spark plug tube seals can allow oil to leak into the wells and to seep down the plug threads, inhibiting the ground path for spark and leading to plug fouling.

Take great care when cleaning any precious-metal spark plug. The iridium electrodes on your IFR plugs are very small and easily damaged, which is why NGK states that the gap is set at the factory and that under normal circumstances it should not be adjusted.

Cheers,

Don