Hello gents,
Without fail I have another issue on the XJR. Thursday morning while on route to work I stepped on the gas to overtake a car upon slowing down I noticed a very rough idle. No mil light until I stepped on it again but flashing. Let off The gas and eased why easy to work. The mil light finally stayed on when I arrived to work. Got codes p300, p304, p305, I forget from memory the last 2 codes but they're exceeds emissions and potential catalytic converter damage. Usual codes I expect from a misfire.

The spark plugs are only 2 years old, ngk, and the coils are less than a year old, airtex wells. I went ahead and replaced the spark plugs and switched coil 5 to 3 and coil 4 to 2. Also there was quite a bit of oil in spark plug well number 7 and a little in number 5. See pics below.
Turned the car on and still getting a misfire. I'm now getting the same codes minus the p304. I'm ordering valve cover and plug well gaskets to fix the oil issue.
Can the oil in well 7 be bad enough to cause a misfire even with a new spark plug? Can oil toast a good coil? Am I looking at a stuck fuel injector? Or should I be looking at something else?

Not gonna lie gents its been ongoing issues with this car the past 2 years. With it being my daily driver I'm losing the jaguar spirit. I'm spending more weekends under it than in it. Ok, now that I have vented let me know your thoughts.
Thanks in advance!

plugs from top to bottom: 2,4,6,8 and 1,3,5 and 7
Oil in well 7
Plug 7
Plug 5

 

Hi BlackKat,

There's not really anything unusual about misfires with oil on the spark plug threads because the threads are the ground path for the spark circuit (via the engine head/block and engine ground strap). The oil adds considerable resistance to the electrical circuit, leading to misfires, especially under load.

I'm guessing the other codes you received may have been along the lines of P1313, P1314 or P1316, which indicate multiple misfire events or misfires severe enough to cause damage to the catalytic converters. Here's some info from the Diagnostic Trouble Codes Summaries Manual:



You can download the manual here:

X350 DTC Summaries Manual

Replacing the cam cover & spark plug tube gaskets should solve the problem. You probably could have just cleaned the threads on your old plugs, but even with new plugs you should also clean the threads in the cylinder head. A bottle brush wetted with throttle cleaner works well, but if you don't have a suitable bottle brush you can wrap a cloth around a wooden dowel and wet it with throttle cleaner.

Cheers,

Don

 

Flashing MIL = severe misfires causing catalyst damage

Avoid that - cats are costly!

Yes oil can damage coils.

 

Thanks for the replies gentlemen.
I rechecked codes today and here is what I have after the plug replacement and coil switch.
p304, p305 and p1316.
The part that worries me is p304 which corresponds to cylinder 4 which is on bank 2. All the plug wells in bank 2 were clean and free from oil. I had switched coils 5 with 3 and 4 with 2 yet I'm still getting codes for cylinder 5 and 4. I can understand cylinder 5 since it has some oil but not cylinder 4. Plug well 7 head the most oil but no codes for cylinder 7. Maybe I'm over stressing myself.
Anyways I ordered a cam cover gasket, plug well seals and a new coil which should arrive in a couple of days.
Let me know your thougts.
Thanks again guys!

 

It wouldn’t hurt to replace the PCV valve if you haven’t done so recently. I had random misfires recently documented in this thread:

https://www.jaguarforums.com/forum/x...unning-193855/

Though the coils and plugs were due to be changed, replacing the PCV valve took away most of the misfires except one, which was the problem coil. Also, have you read your fuel trims out of curiosity?

 

***Edit***
Pictures didnt load on mobile. The oil on the spark plugs is also a likely canidate. If that doesnt solve the misfire consider looking at your cats.
***Edit***


Just delt with the same on my 05 Super V8. below 4k rpm It would pull hard as hell. Above 4k it would misfire and pre-detonate so hard I could hear it inside of the cabin, and then shut down the whole bank (bank2) of cylinders. The cause?

The cat was clogged. Seriously. Gutted it for temporary use and the car has GOBS of power that I never knew it had when I purchased it a few thousand miles ago.

I did everything. I am a Jaguar certified mechanic and it was driving me up the wall til I remembered an older XJR I had that did the same thing. I took the cat off (my car isnt rusty so no broken studs but have a shop do it as youll HAVE to heat the exhaust flange nuts and the squeeze clamp) and then removed the 02 sensors and filled it with water from a hose. basically NOTHING was flowing through it.

I replaced all the plugs with new NGK plugs, New OEM coils, a new MAF, did an induction cleaning and ran BG solution through the fuel injectors which does a great job fixing lean conditions. Nothing helped til I gutted that cat. Will be doing a full exhaust now with 200cel magnaflow cats.

Before I purchased the car it had a failed Intercooler pump and a failed MAF which wasnt addressed for nearly two years!!! that is why my cat clogged, car had lean codes prior to my purchase and a failed MAF code (the guy put a cheap aftermarket MAF on it)

Not saying 100% your cats are clogged.. but.. something to consider. Good luck.

 

Sorry for the delay in reply gang. I replaced the valve cover gaskets along with the rubber grommets for the valve cover bolts. FYI the gasket and grommets came together as a kit from not RockAuto good price however it was short 4 grommets. No worries I reused 4 old ones that were still good. Plugged everything back up and still misfire codes p0304 and p0305. I replaced coil #5 which was previously coil #3 ( I switched them last time) with the new coil. Voila fixed. So it was never coil #5 nor coil #4 but coil #3 and/or cobination of valve cover gasket seals.
P.S I also did a compression test on that bank while I was at it, checked out to be consistant.