hi Guys, I am new to XJR ownership but own a number of Jaguars, an early series one XJ12 and I have just finished restoring a 1962 3.8 e type FHC. Anyway, I am pretty practical but have not trained or have much experience of ECU controlled vehicles. I have just bought myself a 1999 XJR with just 77,000 miles on and a good and extensive service history. When I collected the car, I was not wowed with the performance and felt that perhaps either it was not performing as it should or I had overestimated the allure of the XJR. Anyway, I got home ok, and used it for a couple of days, then I decided to see whether the cruise control worked. Big mistake as all my problems then started. I turned on the master control, then hit the set on the steering wheel and ping! up came a message saying engine failsafe mode ( I think ) . Damn . I thought that was it and I would not be getting home. Anyway I had to stop the engine as I was at my destination and did not want to turn right around. When I restarted it the warning had gone and the Jag drove as it had before. However when I got home I went to open the boot. Nothing, went inside the car, dead. All electrics had dumped and the instruments were sort of on reading half, i.e they had not returned to zero. I was advised to take both battery leads off and leave it for an hour. This I did and when I recoupled the battery , hey presto I had a working car again for a while. I was immediately aware of the fact that it seemed a lot quicker. Anyway, after doing some steady motorway work, the throttle response seemed odd. It changed its characteristics at least 3 or 4 times during the journey and when I stopped the car, it was dead again. Did the same battery trick and this time it revved at 1200 rpm and would not slow down.


I realise this is sounding like an earth problem so have checked the battery voltage and this is 12.4v when engine off and 14v plus when running. I have the same readings at the terminal through the second bulkhead above the servo. That is as far as I have got . I had read it could be a bad earth on the ECU , but so far have gone no further. where is the ECU by the way? Anyway, if some kind soul could give me some pointers I would be very grateful indeed. Also, is it worth me buying a code reader off E Bay, if so which do you all recommend? hope to get some intel soon, thx Andrew

 

First, 12.4 V is not really enough. Try charging the battery and see if you can get it higher. A lot of odd electrical occurrences are just due to a weak battery.

There are many connections to both the + and - side. A major ground is from the back of engine to the frame. Also look at the + to the major fuse pack in the boot. Several members have reported a bad crimp to the battery cables.

 

I would suspect that a majority of the active members on this forum have a code reader. If you have an Android phone you need to explore the TORQUE app that is a free download. You would need to add an OBD to Bluetooth converter available on eBay or elsewhere for $10 and you have a full feature reader. iPhones do not work with TOQUE.

Or you could read through this thread on forum member's feedback on code readers:

https://www.jaguarforums.com/forum/g...oved-**-33347/

 

I've had several brands and several different systems for OBD. I have VCDS for Volkswagen's brands of cars. My snap on MT2500 is extremely robust for many different makes and models.

The easiest one I keep around to let people borrow, keep in the car on trips, etc; is an AutoXRay EZScan 5000 that I picked up real cheap at $100.

I definitely recommend owning some sort of OBD2 scanner, whether it's TORQUE, a dedicated simple pocket reader or something else. I actually prefer scan tools to do active monitoring rather than just simple code reading, but buy a cheap code reader and if you find you need more used ones sell fast and you wont be out much!

 

Does the extensive service history give you the age of the battery? Sounds like you need a new one.

 

I use an Ultragauge scan tool, mounted on a small bracket that slips into the gap under the center panel. It is useful for temp., fuel trims as well as read and clear engine codes. $70 online last I checked.

 

Couple things

As others say, the base problem of all the wild symptoms may be the battery.

Once you sort that situation, the cruise fault you reported may be unrelated to the battery - the most common cause of the symptoms you indicate are a bad microswitch that is located on the back of the brake pedal.

For scan tool & code reading, a couple more suggestions. I'm a Mac user, so am using a wifi OBD2 dongle (Apple doesn't like Bluetooth). I bought a cheapo clone off eBay & have paired it to both OBD Auto Doctor(bought the full license) and Movi Pro (trial only) - both are good & present all the data needed in all the cars/trucks driven by the extended family 95+% of the time. The dongle I got is capable of being read by my machine in the house from over 50 metres away - helpful only in that it is more comfortable to run it from there, on a large screen (great for the scope functions) than while sitting in the drivers seat. I'm thinking of spending the extra dollars to get a true ELM327 (latest version 2.1) as the cheapos have less functionality as they are basically clones of the 1st gen ELM327 &, as many have reported, can be flaky & short lived (I still have more functionality with my this setup that cost <$50 CAD all in, than my hand held Innova scan tool at almost $200)

 

Thank you for the replies and ideas. I will check out OBD readers but I use an IPhone so that limits my options.

I had read about faulty brake switches but events rather over took the original issue. What should the battery be at rest then? Over 13v?

 

Battery voltage "at rest" is a very poor indicator of battery condition UNLESS it is below 12 volts, in which case you can say definitively that the battery is either discharged or bad. A quick easy test is to turn on the headlamps on high beams (key on, not running), and see if youstill have 12.2 or so volts. Better still is to check the voltage at the battery while cranking, in which case a voltage above 11.0 or so is good.

Charging a battery only fixes a discharged condition. It does not do anything for a failed or failing battery.

 

The battery should be at least 12.6/ 12.7 volts at rest, and 14.4 with the engine running.


On my 98 XJR I had the same cruise control problem.
It was a broken vacuum line just in front of the centre of the bulkhead.

 

A lead acid battery's voltage is highly dependent on temperature, age and to some extent, on construction chemistry. Exact voltages vary!

 

. . . yes but if you see something approaching 10v while cranking the electronics will not even start the car.

These cars are perfectly capable of spinning the engine without the ability to start because of the voltage to the electronics.

 

ok well consensus seems to be that the problem is battery voltage related, or at least I need to eliminate that as a cause. I remain to be convinced as I find it hard, not doubting anyone, to believe that 0.3v or so will make that much difference to the ECU performance. Where is the ECU on a 99 XJR, does anyone know? I will also try to climb underneath and check some earths. I imagine the ECU earth is right next to where it is located.
Reference the battery, I think I should be able to tell the date from a serial number on the side. Will report back

 

These Jaguars are EXTREMELY SENSITVE to voltage, if the battery is not 100% you will drive yourself bat crap crazy chasing all the random non starting, warning messages, and electrical glitches that can arise.


If the voltage drops below what the ECU needs, it has a brain fart, and makes things up.


There are multiple ECU s all over the car, see the electrical guide for exact placements.


If it were me, I would start with having the battery checked, then clean all the earths and power connections including the two in front of the spare wheel.

 

being a bit of a suspicious so and so, I am reluctant to speak too soon, BUT.......I may have sorted it thanks to you guys.


I checked out the battery, 12.4 v but called Bosch who told me it was a 2005 battery. Well I just bit the bullet and bought a new battery, Bosch again, probably stupidly but I thought I would go for a well known brand. I have just covered best part of 50 miles and nothing untoward happened. The high revs reverted back to normal, the central locking worked, the throttle response seemed fine. The only possible glitch was that the filler cap did not open until I locked the car and opened it again. But so far I am delighted.


anyway, providing this is cured I can now concentrate on a few other bits, rattles in the doors and a squeak under the dash top in the middle.


many thanks for the help, and fingers crossed its sorted

 

I am trying to get the hang of this forums engineering but here is a photo of the offending Lady. Back in my good books.

 

Very nice ride, and doesn't it feel good to have all of those weird issues resolved by something as simple as a new battery!!

 

She does look nice and clean.


Just hope she behaves herself for a little while.


As the lid of my toolbox says, " If its got t*ts or wheels, at some point it WILL give you grief "

 

I agree with the statement that .3 volts should not affect the ECU, but I have a theory about the X-308 battery sensitivity. That is that the average battery voltage is not the problem as much as it is that failing filter capacitors in the modules makes them sensitive to voltage spikes in the supply. A failing battery has higher impedence and will therefore not suppress the naturally occurring ripple and spikes from the alternator. I have not yet put a scope n an old battery, but I will someday to check this out.

 

interesting theory which is slightly beyond my knowledge of battery technology but sounds perfectly feasible. I guess simplistically I compare it to a home pc or laptop. I know that if I were to mess around with the voltage supply to that I am sure the computer would have a brain freak in much the same way as if you switched the power on and off momentarily ( assuming that you were running it on mains only) which would simulate bad earth on the car . Anyway, when I saw the battery was 10 years old it was a bit of no brainer to go with the advice here. Long gone are the days when a battery was ok if it would crank the motor!!