In summary :
2000MY XJ8 4.0
Car starts / runs OK from cold in morning.
Same after work 7-8 hours later.
Same after brief stops (5-10 mins say).
If the car is left for about an hour after a run (after a shopping trip say), it starts but with CEL and Restricted Performance message. Engine is rough like its not firing on all 8. The following morning it starts / runs fine but with CEL and RP message. This goes away after about a minutes driving and all is well.
Then the cycle begins over again the following day. I did in the past get this but only once every 6 weeks or so, but now its every day.
Have cleaned TB / coil connections, cleaned MAF connector and TB itself, to no avail. It has newish plugs/ air filter / oil / fuel filter / upper tensioners etc.
The air intake / breather hose show no signs of cracks.
I am waiting for a scanner I've ordered so I can hopefully pull some codes but I wonder if anyone here has had a similar scenario. The RP/CEL only seem to occur after a specific time at rest after a run - I am thinking of coil failure but why only after a hours rest or so ?
Also, if it is coil related has anyone had experience with the Lucas units that many of the Jaguar outlets are now selling ?
Thanks
AndyP

 

Without the OBD codes pretty hard to help, Still, I would run a small bottle of Gumout's best or Lucas's best cleaner through in a tank of gas (petrol).

Betting on oxygen sensors.

 

Check your MAF and any leaks in that line up to the throttle body. There is a seal right after the MAF into that intake tube that I had a leak in. Tape it up and see if that solves it.

 

Thanks to both for replies.
Tried taping air intake by the MAF (I did a hard reset via the battery first) but no luck. I cleaned the MAF wires prior to this also.

While in RP mode the exhaust does smell a little of fuel , which may point to failing coil or O2 sensors I suppose, but my scanner hasn't turned up yet thanks to our postal service (double the cost, half the service). I will have to wait till then as at the moment theres not much else I can do. My MOT is looming soon so I need a fix as it will probably fail on emmisions at the moment!

Regarding the O2 sensors, I assume the upper (upstream) two would be suspect in this scenario...? (grazed knuckles for my grateful indie)....
I'm also wondering about the fuel pump as it has started humming at times....
The thing thats perplexing me is the timing that the RP kicks in, logic leads me to think it may be temperature related somewhere along the line.
I hate bloody electrics, call me outdated but it seems the more sophistication is built into these cars the more likely they are to fail. The last car I had with this many headaches was a 1973 TR6, but with the British Leyland / Lucas (the "prince of darkness") combination unreliability was a given, and owners were disappointed if their cars actually ran well for more than 5 minutes.
Whatever the outcome I'm sure to be a lot poorer by the end of it !

Regards
AndyP

 

Have you checked your Throttle Position Sensor connection (see red circle)? That is what ultimately was my problem with your symptoms. It never threw any codes either, so was hard to diagnose.


Maybe try just unplugging it, spray with WD-40, then re-plug it back in and see if there is any difference. If there is, then definitely do the repair on the plug. After cleaning it and re-plugging, I'd sometimes get a week or two before it returned, but it always returned till I fixed it.

https://www.jaguarforums.com/forum/x...asy-fix-82342/

 

Thanks supersport, yes I did unplug the connector in question (among others) and give it a good spray with contact cleaner, but to no avail. The contacts seemed as new but I suppose you never know .
Hopefully my scanner will turn up monday and I can get some codes (or not).

Many Thanks
AndyP

 

I'm sorry that didn't work. Mine never looked dirty either, it just made the contacts work again for a moment. I usually try the easy stuff first, sorry this one didn't help.

If you find the source of the problem, please post back for future readers.

 

Well I got my scanner today.
With the engine cold and no CEL, I got the following stored codes :

P0308 Cylinder #8 misfire
P1316 Injector Circuit / IDM codes detected
P0356 Coil F circuit malfunction
P0358 Coil H circuit malfunction

Regarding the last 2 codes, I've looked up the V8 cylinder numbering and there seems to be 2 systems :
http://jagrepair.com/images/AutoRepa..._numbering.pdf

Anyway I am looking at bank 2 (UK passenger side) coils yes ?
If so thats better because I don't have to remove the air intake for access ! The coil packs on this bank all seem a bit rusty indicating water damage.
Should I just replace all 4, or have the circuit tested first ? I have a small multimeter but how do I go about testing? (I'm a complete novice at electrics btw...).

[amendment]
In fact thinking about it the coils got swapped around a couple of weeks ago as I removed them all to clean the connectors, so would it be logical to assume the 3rd code was generated first with bad coil on "F", then got swapped to "H" generating 4th code later...?
Regards
AndyP

 

I believe that would be coils 6 and 8, which are number 2 and 4 on the LH side from front to back. I would pull those four coils out, check them out, pull the boots off and clean them up and stretch the little springs in there to make good contact. Then try putting them back in positions 5 and 7, reset the cdes, and see if the codes move.

 

Thanks JimmyL.
To update this thread :

Codes cleared.
Car left for 1 1/2 hours after run.

Restarted - CEL and RP messgages.
Code P0358 thrown (Coil H malfunction - cylinder #8).

Cleared code.

Swapped Coil H and Coil E around.
Restarted - CEL and RP messgages.
Code P0355 (Coil E malfunction - cylinder #5)
Code P1316 (Injector / IDM codes detected)
Code P0305 - cylinder #5 misfire

From this it seems pretty conclusive that the coil is defective.
I will be ordering new coils ASAP , probably the whole bank of 4, with the others to follow shortly.
Without my cheap scanner I would no doubt have had to pay out on 1/2 hours labour at the garage - so its more than paid for itself already !
Thanks to all who chimed in, I will report after new coils fitted.

AndyP

 

Good job on finding it! Keeping a 13 year old car running without your own scanner is a financial risk.

I would save the money and just replace one coil. At least on the older Jaguar coils, the replacements are reported to be much less reliable. And there do not seem to be a whole lot of X-308 coil failures.