XK 5.0 Ltr miss fire

[Sev90]

I'm starting to loose faith with my 2010 XK which I brought 6 months ago as I seem to be plagued by a recurring issue with a misfire and reduced performance message.

The dealer I purchased it from gave a 3 month warranty and used a local garage to do all their warranty work I thought it was a safe bet. When the problem first happened they had the car checked it out deleted the faults and returned it saying "It seem ok" I will add that even thou it was misfiring and running rough when I booked it in by time I took it to the garage it was running perfect again. So weeks went by with no problem but I hardly drove it in that time then we set of on 300 mile round trip to Norfolk got there no problem set off home and the misfire is back, pulled up plugged in the Topdom cleared the faults and away we go only for it to return 20 mins later. Stopped at a service station contemplating the AA to start it up and drive 120 miles home with no problem. Booked it back in at the garage to be told there's nothing wrong so left it with them for a few days to run about in till the fault reappeared which it didn't all they manage to do was send it back looking like the back of a farmers landrover so it won't be going back to that place again.

After a few weeks it reappeared the dealer now long past my warranty period suggested a local Jag specialist to do a diagnostic check which they said showed, coil pack 2 faulty and injector 6 faulty and a quote for £1100 to sort. the dealer suggest I return the car so their in house mechanic can do the work and threw in a new set of plugs and it wouldn't cost me. Great we finally sorted but no a week later and it's miss firing again and I had only drove a few miles. I've contacted the mechanic  who said he will have a talk with his boss as he wants the car right but I think the boss is losing interest as I've had the car 6 month and it's looking like an expensive job.

Has anyone had similar misfire problems or any idea as I now own a very pretty ornament on the front which I just don't trust to drive anymore.

Pete.

[N6 JMX]

Hi Peter, when a misfire occurs there should normally be stored codes (DTC) that can be read by a suitable OBD code reader - diagnostic system. Ideally, this should either be the Jaguar Diagnostics or the Auto Logic system. These codes are key to fault finding on a Modern XK.

If the fault is intermittent and one coil pack and injector has already been replaced, there could well be a waterfall effect for other coil packs and / or injectors - they are all of the same vintage of course. As an aside, if your mechanic is not familiar with Jaguar's numbering, he may well have replaced the incorrect offending parts in the wrong location. The following info is from the Workshop Manual:

References to Bank-1 and Bank-2: References to Bank-1 and Bank-2 are made with regard to the engine. When viewed from the flywheel the right-hand bank will be Bank-1 and the left-hand bank will be Bank-2.

Cylinder numbering: The cylinders in each bank are numbered from 1 to 4, with number 1 at the front. Comment: from this, which is cylinder number 2 or 6? Requires additional definition

In other words, have the correct parts been replaced in the correct locations?

Another possible cause of a misfire is a vacuum leak, which can be notoriously difficult to locate, but a smoke test of the pipework could show up a possible leak for investigation.

Hope this helps with the fault finding.

N6 JMX

[Sev90]

Hi Jim

The cylinder numbering I find very confusing but the diagram I have shows bank-1 (driver side) front cly to be number-1 then working backwards 3-5-7 . then bank-2 (passenger) starts with number-2 at the front and 4-6-8 as you work back. With you mentioning mixing the clys up I have pulled off the plastic cover and looked down towards the coil packs and the second one back from the front bank-2 appears to have a shiny new black coil pack where as the rest are all dusty grey but according to the diagram I'm looking at should be number 4 not number 2 this leads me to question which cly has the new injector that was suppose to be cly 6. Looks like it's time to give up on the dealer sorting it and crack on with replacing the lot at my own expense not what I purchased it for as my original plan was a X100 but decide against another long term project car in favour of a car to drive. Now that seems to have come back to slap me a good un around the chops.

Pete.  

[Jaguar Owners Club]

Many years back a lot of mechanics were caught out by the firing order on the XJ6 engine.
Bizarre as it was, the number 1 cylinder was at the back of the engine and the cylinders then ran to number 6 cylinder being at the front of the engine.

Urban myth is that the original blueprints were upside down when the engine was manufactured - how true that is I'm not sure but it did cause many problems for years to come.

So, quite possibly the incorrect cylinder location could be a possibility - easily diagnosed by swapping components from the affected cylinder to another one and see if the fault replicates there - this also proves it to be either an injector or ignition fault rather than being the cylinder at fault (e.g. compression, etc)
Also if the misfire is current when testing an infra-red temperature gauge can read temperatures on each cylinder and the one(s) that are reading lower temperature are possibly the location of the misfiring cylinder