Smog is due for the XJ8 in 10 days, and yesterday a rough idle and P0357 showed up. <sigh>
I pulled the ignition covers, started the engine and wiggled the wires to make sure there was not a wiring issue. No issues were observed. A side question, are the brass inserts supposed to stay in the head? On our car, none of the bolts came out, i ended up pulling the cover and inserts off, and only three bolt holes were intact.

I pulled the spark plug, it is a Bosch FR7DPP30X, gap is 0.040". There is oil in the plug well, so i presume i will have to change camshaft cover gaskets. Tensioners need to be done, so I will do that them.

My questions are:
What plug should be in the car? MY 1999 138k miles
Does anyone have any long term experience with the lower cost coils that are available? I was originally thinking about replacing just the one coil, but if i am doing the plugs, i could do the coils at the same time.

 

Hi studeb,

It is very likely that the oil in the spark plug well has contributed to failure of the ignition coil in cylinder B3. The spark plug thread-to-cylinder head thread is the ground path for spark, and if oil has seeped down those threads it can add considerable resistance to the ground path, which causes the coil to overheat and fail.

Since you probably don't have time to replace your camshaft cover gaskets before you have to get the car through emissions, it might help to remove all of the spark plugs and clean their threads, and clean the oil out of the spark plug wells. There are a number of ways to do this, but an easy method is to wrap the corner of a paper towel into a small wad around the end of a long flat-tipped screwdriver. Insert the screwdriver tip/wad down into the plug tube while holding the opposite corner of the paper towel with your other hand. Twist the screwdriver to swab the oil out of the tube. Just pull up on the corner of the paper towel in your hand to retrieve it. Repeat as necessary. Once you've swabbed out as much oil as you can, flush the plug wells with zero-residue electronic contact cleaner to flush any remaining oil from the plug threads in the cylinder head. It won't hurt if some of the cleaner drips into the cylinders. It's flammable and will combust with the air-fuel mix when you start the engine. If you happen to have a long-handled bottle brush small enough to fit down into the spark plug threads in the head, running it down the threads wetted with electronic cleaner will improve the cleaning process.

According to the Vehicle Specification Booklet, which you can download at the link below, the correct spark plug for your 1999 4.0L is Jaguar part number AJ8 4575 (iridium). The actual manufacturer is NGK and the part number is 7866 / IFR5N10. This is the Laser Iridium spark plug. It is possible that your car was originally equipped with the Laser Platinum plug, 2647 / PFR5G-11, but Jaguar changed its spec to the iridiums by the time this spec book was published in 2003. The iridium plugs last longer but performance should be the same with the platinum plugs.

Jaguar Vehicle Specification Booklet 1997-2003

I don't have any experience with the cheap coils, but since the original Denso coils have become difficult to find I have used the NGK coils from Rock Auto with great success. I think they run about $65 each plus tax and shipping. But be sure you get the correct coil for your engine - there are 2-pin and 4-pin ignition coils depending on year & engine.

Replacing the one coil and cleaning the spark plugs and tubes, clearing the codes, then driving the car for a few days to reset the diagnostic readiness monitors may get you through emissions. Then you can plan on replacing the cam cover gaskets, plugs, etc. later.

Cheers,

Don

 

Hi Don,

Thanks for the reply. That booklet is very informative, and will be useful.
Coil and plugs have been ordered, ill clean all the plug bores while i am there. The next item up is the changing the driveshaft carrier bearing and flex disks. I will do the gaskets when i renew the timing chains/tensioners this summer.

 

Today's update:
New plugs arrived, NGK 7866. I swapped them out. I did bank 2 first, plug 1 was dry, 2 had a bit of oil, 3 and 4 had more. I noticed that the oil fill cap is above #3, thought that maybe it is not the camshaft gasket because #1 was dry. Did bank 1, and found the same pattern, 1 cleanest, and 4 was filled with oil, probably up to top of plug. So both gaskets need to be done. I cleaned them all, and torqued them to spec. The last person who was there put them close to 90lbs of torque. I have attached a shot of the plugs, bank 1 on top, 2 on the bottom, 1 to 4 is L to R. You can see the amount of oil in the well for plug 1-4. They are pretty badly fouled, i think its oil. There i no screen for the full load breather, should there be one? When i got the car i cleaned out the part load fitting, it, it was blocked. However i did not clear the line out. Do they get clogged? Air filter needs to be replaced as it has taken up a fair bit of oil.too.


Bank 1 top, 1-4 l -r