V6 Spark Plugs

[Bellajag]

Lesson learned. In June 2013 I had new plugs fitted to my 2.0 V6. The plugs that came out were the original factory ones! They were not causing a problem, I had new ones in because I'd had the car 3 years and didn't know if they had ever been changed. Since then it's had an intermittent misfire especially at low revs, say in fifth gear at 30 mph. On motorways it never missed a beat.
As the misfire was slowly getting worse I returned it to the garage and they found that one plug had been very hot and burnt away the electrode. They have now fitted platinum plugs and she is back to her old self.
Maybe lesson is not to fit cheaper ordinary plugs to these cars.

[J44EAG]

Spark plugs must be kept up to scratch with most modern cars that are fitted with individual plug on coils.

Plug misfires need attention immediately they occur. Failure to attend the matter will soon destroy any plug on coil which is fitted to a tired misfiring spark plug.

On V6 X-types and S-types, the three plugs buried under the inlet manifold tend to get neglected. To get to them the inlet manifold has to come off. That is work which can sometimes, whether deliberate or not, get ignored and those three plugs can end up becoming very high mileage before someone eventually gets around to changing them. In the intervening period those plugs begin to break down and then cause coil issues just mentioned.

It is well worth buying long life plugs to attempt to double the time between plug changes and inlet manifold removal. Labour tends to be rather more expensive than a few extra ponds spent on higher lifed plugs.

Mike.

[steve_m]

Reviving an old thread here.
Just had new plugs fitted as I don't know when they were last done (2004, 2.5 V6,115,000 miles) as part of a of a service.
Done less than 100 miles and I'm starting to get the same symptoms as posted here.
Didn't check the plugs myself as my guy did the work and the service kit came from a Jag independent and I'm sure that it said OEM ones were in the kit.
I'll have a check around for any obvious loose connections but is there anything else I should be looking at?

[J44EAG]

Go back to coils, Steve and replace as needed.

Mike

[steve_m]

Thanks.
Unfortunately I have to leave home at 0500!
Took it down the local garage but their code reader wouldn't delve deeply enough in to the system for a full diagnostic.
It came up with a throttle body problem and they found a service bulletin relating to DTC P1582 (Flight recorder) which comes up if any of the following conditions occur:-
1. Inertia switch activated
2. Throttle failure causes default limp home mode
3. Engine starts and stumbles
4. Engine fails to start
5. Engine stall

1, 3, 4and 5 don't seem to apply and as far as 2 goes it hasn't gone in to limp home mode and there are no warning lights.
It seems to stumble if trying to accelerate in too high a gear or when slowing down and then trying to pull away in too high a gear.
Constant speed or changing down and accelerating doesn't make it stumble.

Looks like I will be dragging the XJR-s out of the garage!
Which had a flat battery this morning!
'Cos I didn't shut the boot properly.

[steve_m]

If it was a coil pack playing up would that not generate it's own code?

[BrizzleJag]

For about the past fifteen years whenever I have replaced spark plugs I have always gone for Iridium, because (cribbed from the net)...
A lower voltage is required, this reduces load on a vehicle's ignition system (less strain = less chance of failure)
A larger gap can be supported without increasing load on the ignition system (Larger gap = larger spark = more efficient combustion)
A more precise spark every time, delivered in the correct position and with the correct timing (More efficient combustion)
Assuming a suitable Iridium plug is available, benefits you are most likely to see are:

Improved throttle response
Improved economy (though this depends largely on how much you enjoy the improved throttle response!)
Increased plug service life (Depending on design, an Iridium plug could last up to ten times the life of a standard plug with little reduction in efficiency over the plug's lifespan)
Increased engine power (Don't expect to double your horsepower but a 1 - 3% increase is possible)
Improved (reduced) emissions.

[steve_m]

Thanks for that but doesn't really help me.
If a coil was failing would it not show up it's own code?
What problems can you get with the throttle body that would throw up the code that was generated?
DTC P1582.