2006 XK8 finally arrived Monday evening. Drove it around town and on the highway for over an hour getting to know my new friend. Was low on fuel so filled up with Sunoco 93.

Did not drive it Tuesday.

Wednesday morning took it to work. At the first traffic light started rough idling and the Restricted Performance (amber) lit up. #disappointing. Shortly after the Check Engine blinked a few times and went out. Drove a little while, pulled over, restarted and all was well for the rest of the trip in.

Driving home the rough idle and amber warning started again. And now check engine stays lit. A few miles down the road and I got the red Coolant Low indicator. Pulled over and checked the reservoir. It was full. Drove home with all of the above lit, anxiously watching the temp gauge.

Assuming these are unrelated. From reading the forum sounds like I have a stuck or failed float in the coolant system. Have not read any codes yet. Could my choice in fuel be related to the rough running?

 

Could be lots of things but I'd start with suspecting bad power (or ground) and that is often a failing / flattish battery.

 

You're gonna need an OBDII code reader. There is a wide variety and a lot of posts on here about this. It is essential and not expensive. The low coolant could be due to a stuck float, also check the wire connection to the sensor on the bottom and make sure the sensor is seated in the bottom of the reservoir. It just snaps in (sensor).

 

I have to agree with JAGV8. The cat doesn't like any kind of electrical loss. It does all kinds of crazy things.
First your choice of fuel is fine it isn't causing problems.
Second if the check engine light is on get the codes read and post as soon as you can. Most auto parts stores will scan for you. Ignore their diagnosis and post the actual numbers.
Third since your problem takes a little while to manifest itself I would remove and clean the battery connections. Wouldn't hurt to have the battery load tested. I would also check the bulkhead connector under the bonnet. It is a connection for the cables from the boot to bring power to the engine compartment. Remove, clean and tighten the connections.
Last I would take a look at the ground connection that runs from the engine/transmission on the passenger side to the frame. Make sure it is clean and tight.
I really think a loose connection is causing a heat build up and increasing the amp draw away from the battery. Once battery voltage starts dropping the computer modules start going crazy.

 

+1 on battery

If it is more than a couple years old just replace it and see what clears up. Odds are good that will make a world of difference.

 

besides rebooting the windows is there anything else I have to be concerned about with swapping the battery?

 

Not really. Worst case, the battery is out hours and it's the equivalent of a hard reset. That just zeroizes learning modules/ecu---not necessarily a bad thing.

I'd pull the codes before putting any money anywhere but you really can't go wrong with a new battery.

 

So I poked around the engine compartment for 3-4 min before I realized the battery was in the trunk. unfortunately no dates on the battery as far as I could tell. I'll pull it tomorrow and get it checked. No obvious issues. Terminals were clean. Connections seemed solid. Battery is not new, but didn't seem particularly old either.
Wasn't able to make much from the battery label

 

Follow the thick braided strap. Many have reported contact issues with frayed ends that caused problems. You can search for more details.

Best.

 

A Rolls-Royce battery

There looks to be a date code stamped on the terminal but I can't make it out. Usually week or month # and last 2 digits of year. Can you decipher it?

However, a proper load test will confirm its condition.

Mike

 

Good eyes Mike! Date code 4606 on the negative terminal. Couldn't find confirmation on a Rolls battery, but on a BMW battery that would mean it was manufactured in week 46 of 2006. Hard to believe that battery is over 10 years old!

Car was manufactured Feb 2005. Wonder why it would have a late 2006 vintage battery? In any case I suppose I should start with a new one and see how things act after that. Thanks all.

 

New battery. Same issues. Going to have to get those codes.

While I was in there replacing the battery I noticed these wiring harnesses not plugged into anything. Anybody have any idea what they are (circled in purple).
That's the positive battery cable at the top of the pic

 

Battery is definitely RR part #:
https://rolls-royce.7zap.com/en/roll...0-usa/61/1607/
Other than the label, it's doubtless the same as that supplied to us lesser mortals - although if it's done 10 years... Anyway, one thing to cross off since you've replaced it. You do need to get the codes out to get you pointed in the right direction.

The unused plugs in the trunk were for transit purposes, AFAIK.

M

P.S. I'd grab the 1¢ before anyone else spots it...

 

Haha I did grab it. It was a 1987. Decided to leave it there for the next guy... Or me in another 10 years.

 

Thanks to the good folks at autozone I now have codes:

Where to begin....

 

Could be wiring, bad injector, etc. Fix it soon or you may also need a cat conv - P1316 is severe misfires!

 

From reading first post, I would say a coil or two are failing. Numbers 6 and 8 tend to go easiest, with aging plugs. Dunno why. but seems you now confirmed this. Best is to change plugs, and the 2 coils. But use only Jag OEM coils. The cheap ones are crap. And hope not too much raw fuel dumped into one of the cats. That flashing check engine, means they are in danger. Dont drive! If a cat is damaged, it will trip a code P0420 or P0430.

 

also for those trunk plugs. The 2 wire one is a battery kill when in shipping. Un-installed at dealer. The 3 wire is for adding an optional trunk mount accessory 12 volt port. One wire will make it always live. The other, when a relay is installed in missing socket in trunk fuse box, will make it switched. Last wire is ground. there is also another of these behind the glove box, for a port in there

 

I finally got my hands dirty. Pulled all 4 coils on the left bank. Could find nothing unusual (oil or water in or around the coils or plugs). I did not pull the plugs. I did swap all 4 coils (2,4,6,8 went to 8,6,4,2). Once again I got maybe 10 min of good driving before the misfires started. Checked codes and it still showed exactly the same. Though I should note I had not cleared them. I did not see any new codes, say in 2 or 4.

Attached is a pic of what was the #8 coil. It was slightly different from the rest in that it had a reddish appearance. Any clue there?

Lastly, one more pattern I've noticed. From a cold start I get the misfires almost immediately. However once I've driven it up to operating temp, then let it rest for maybe 10-15 min, I get any where from 15-30 min of clean driving before the misfires and restricted performance begin.

thanks
The one from #8 on the left. #6 on right. #8 is where the codes are pointing
2006 XK8 4.2 65k mi

 

Hey Hi.. Been reading a little of this. I'm a fairly new member. Joined when I bought a Jag back about 6 months ago... Already,,, me and mine,,, have been thru a LOT and I find this site invaluable. If it weren't for it,,, I wouldn't have been able to buy or afford this car.

This might be my first time commenting and offing a suggestion, but here goes. When I got mine I was getting codes for misfire too. I replaced battery as well. Helped with LOTS of things but not misfire codes. I purchased a couple of new-ish coils, changed plugs, swapped fuel injectors and replaced a couple of those as well. All I can afford is used stuff right now. Still, nothing ever really did it and, spotty, here and there, I continued to get misfire codes. They suck. Here's what I did that completely ended that for me. (see pic) I promise I'm not promoting or advertising anything, lol

Maybe it seems ghetto but ONE THIN WRAP with this, from bottom of the coil almost to the top of the coil post, worked. I stress one thin wrap because if your spark plug hole is like mine, more than one thin wrap will prevent the coil from fitting back in properly/easily. MORE, a good blob of di-electric grease in the spark plug end of the coil. I've never had a misfire or that bouncing idle again.

What I noticed when I was testing for spark and trying to figure out my misfires was that,,, the way the coils are made, with even the slightest damage, misalignment of boot, scratches on coil stem, anything, even just with age - spark was jumping out of the coil all over the place. At that seam, out of the rubber boot on the side (which I think has to do with the red you mentioned), scratches on the hard plastic stem. What a mess and strange design. The silicon wrap was a shot in the dark 'cover all' (literally) and it worked, di-electric was a bonus.

Hope that helps.