Dead battery/duff alternator? XJ8 3.2 Sport 2001

[jagian]

Has anyone experienced starting problems after the car has sat on the drive/not moved for 2 days/nights? The first time it happened the NU/RAC guy said it just needs a good run as the voltage had not dropped disasterously. However a few nights later it happened again and the next NU/RAC guy said dead battery. So £90 less and a new battery later guess what happened this morning after the car had not moved for 2 days/nights? Yep couldn't even open the door without the key.
The car was already booked into my local Jag Dealer's this Thursday (9th Feb)for n/s bottom bushes to be replaced (see "Knocking from rear" thread)but their Service Dept are slightly puzzled as the battery is charging OK and the alternator also seems to be working efficiently (according to NU/RAC guy).

[eldudereno]

As with any car, you've got to look for current drains. I'm no Jag expert but the first thing I'd look for is sticking light switches, especially those in the boot or under the bonnet.

[jonywishbone]

I did this on an old xjs so please check that disconnecting the battery will not need anything resetting such as the abs first. If you can disconnect ok then try this. With +ve terminal only connected connect an ammeter (small multimeter will have this function somewhereon it) say cabable of going up to 10amps between negative terminal wire and battery negative. Make sure all doors lights etc are off. Read the amps it shouldbe something like 0.1 for alarm system and clock etc. From your discharge rate of 2 days you need something like 2-3amps to flatten the battery so you will soon see if something is wrong. If you see a big current then pull the fuses one by one till you see the amps drop. This is then the problem circuit. FWIW on the old xjs it was the boot light so we just left it off. Before that I was reading 10amps until I discovered we'd left the headlights on, we did it on a Paris street and the french thought we were mad ..hours of endless fun though

[jagian]

Had a long chat with main dealer's chief tech guy. He is saying much the same as you.He has also warned me that if they try to find errant circuit it is very labour intensive/time consuming and I may have to remortgage my home.
As a D.I.Y fix he suggests I disconnect the negative battery lead - leave for at least 15 mins and reconnect which should ensure a clean re-boot of all the computer systems. I have also disconnected the car-phone module in the boot as that sometimes causes current drain. They monitored the close down procedure when the ignition is switched off and as each module died the current decreased until everything had closed down then suddenly spiked as a circuit started to draw current again. As there are fuse boxes all over the car finding this circuit is going to take some time.
Thanks for your input - any other suggestions will be gratefully received.

>> Edited by jagian on Saturday 11th February 12:15

[DTYPE]

I have seen a very similar problem on a 2001 XJ8 3.2, battery drain was being caused by a PAS pipe which runs from the rack to the cooler, it runs along the front subframe near to the back of the altenator, this pipe can move up and just touch/rub the back of the altenator. The altenator will function perfectly but once the engine is turned off current will drain down through the metal pipe. All that was needed to cure the problem was a cable tie to secure the pipe to the front subframe. Their was actually a recal from Jaguar about the pipe touching the altenator, worst case senario was that pipe fractures spaying hot PAS oil over back of altenator resulting in a possible fire! Many cars had the recal done (which was to secure hose as described or replace if badly worn) but as is normal many have not. May be worth a quick look, removing the air box lid should give you enough room to see clearly.

[jagian]

Thanks DTYPE this sounds promising. At least it is easy to check whether the recall was ever done.Funnily enough I have just read about this recall from the Fire hazard viewpoint on another forum thread.

jagian