Just thought after some of the things i have been through with my misfires that this post may help others diagnose or fix their misfires. As it seems to be common problem both on v6 and v8.*
Symptoms may include but not subject to Rough/ lumpy idle and or stutter / judder at certain speeds normally 45 or 55mph
Possible causes.
Mil light permanently on or flashing on and off

One thing to note a misfire can bring up a p0420 code which is catalyst running below efficiency.*

1.Chain tensioners failed and chain has jumped one tooth

Possible fix: upgraded chain cam kit generation 3 with metal tensioners.*

2. Coil or electrical plug on coil damaged or wet

Possible fix: replace coil or plug or *dry off all the water. Spray or smear silicone grease onto the electrical connectors and all around the coil pack. So it also seeps down the well. Vaseline the bonnet seal and the top of the coil pack and the rim of the rubber boot which pushes onto spark plug *

3. water in spark plug wells
See number 2.*

4. Oil in plug wells leaking cam cover gasket

Possible fix: replace cam cover gaskets and spark plug seals.*

5.Vacuum leak crack/ split hose or air filter box not sealed

Possible fix: make sure air filter is a good fit and the box is clipped on properly. Check and replace elbow hoses.*

6. spark plugs at end of life or fouled*

Possible fix: clean or replace plugs.*

This is only a quick guide and if anybody wants to amend or add this post feel free

Darren

 

Darren, way to go and a big thank you. We all should be paid a royalty for Jaguar re-enginnering.

 

Darren, I'm going to add my $0.02 as follows:

P0420 or P0430 - cataylist efficiency - doesn't necessarily have to be due to the tensioners failing - when your MIL is flashing - this means unburnt fuel is going through the combustion chamber, through the exhaust manifold and right through the cat converters - those converters are at least 600 degrees F at any given time and the unburnt fuel "burns" the metallic materials inside the converter.

Most likely cause for a P0420 and P0430 is a constant misfiring coil(s) - do not wait for a flashing MIL or worse yet, ignore a flashing MIL - unless you do like spending about $400+ for each converter replacement - one last thing - failing O2 sensors can also falsely flag a cataylist efficiency code, especially post cat converter O2 sensors.

If there is any evidence of oil or water in a spark plug well - the cause must be rectified before replacing a coil - other members have already chimed in regarding water penetration into the engine compartment and as far as oil - the cam cover and spark plug seals must be changed.

I want to go on the record and state vasoline is not going to protect a coil from oil/water penetration issues - that boot should be dry. Personally, I place a small amount of di-electric grease to the inside portion of the coil boot (spring) that connects to the top of the spark plug.

Again, my $0.02

 

That's 2 cents went a long way. Thanks abonano.

 

Big two cents lol. Every piece of info helps. Thanks Dude.

 

I've lost track of the number of times I've posted that flashing MIL = catalyst-damaging misfires.

Other thing to do is check LTFTs (see my sig) because misfire looks like an air leak. And lean codes tend to be the same. See thread in General Tech...