1999 XJ 2.5TD charging problem

[M84AB1]

Originally Posted by Richard buttocks

What is the exact voltage at idle and at say 1500rpm?

At idle (750RPM), the voltage is around 12V. At 1250RPM Voltage is about 13V, anything above 1500RPM Voltage is close to 14V

70% from rated cca and charging voltage was showing sometimes only 12.2 v.
Trying to start the car after a week or two of not been used the multimeter was showing only 10.3 V with key on ignition without even cranking it and therefore no chance of turning over.

Yeah so basically what happened to me. I started noticing that my car took longer to start. It would crank longer than usual. Normally the car starts almost instantaneously. So I started suspecting the battery. Towards the end of the week it barely turned over and once I turned it off, there was no turning it on.

I took the battery out, tested it with a battery tester (100A load) and it was showing bad. Charged it over night with a trickle charger and it appeared to be back to normal. 12.75V and it passed the battery load test. I put it back in the car and within 3 days or so, it appeared to be struggling again until eventually it depleted. At that point I started to think, perhaps these cars are designed so not to engage the alternator at idle and my battery has just lost its ability to hold enough charge. How else could it deplete within a short time period and no I have nothing drawing current.

So now I got a fairly newish battery from my brother, put that in and the issue is still there, no charging voltage higher than about 12V at idle, but anything higher than 1500RPM sits at close to 14V.

There is no battery temperature sensor on mine either

ok, so wonder if we can then assume that the XJs diesel do not have a battery temperature sensor. This is contradicting though to my service repair manual for a 1999 XJ 2.5TD. It even has electrical wiring diagram, see attachment.

[Richard buttocks]

About voltages arent going to help me diagnose your fault.

[M84AB1]

About voltages arent going to help me diagnose your fault.

Hi Richard,

how precise do you want to go? Not even sure what difference it makes whether the idle voltage is 12.2 or 12.1 or 12.0 volts.

At idle voltage is approximately 12 volts, sometimes less depending on the state of the battery.

At 1250RPM the voltage is very close if not exactly 13V and anything above 1500RPM it is very close to 13.8 volts, definitely not 14V or over.

[Richard buttocks]

It matters alot
About 12 could be 11.7 or 12.3
Big difference.

Is the voltage exactly the same at the alternator power terminal?

[M84AB1]

Yeah sure I see.

At idle it can range anywhere between 11.8 and 12.4, depending on the battery state and what is being drawn from it (ignition system..etc), of course I have no accessories on or lights when I do the testing.

At 1250 it moves up to 13 volts and anything above 1500 sits around 13.7-13.9 volts

yeah, the voltage is almost exactly the same as the alternator terminal as it is at the battery. Id imagine there would be small losses as the current supply/demand goes up due to the resistance of the wire. But I guess the question for me is, are these cars supposed to ouput a voltage larger than 13V at idle, or not. Thats why it would be good to have someone with another 2.5TD to confirm or someone who has experience with it.

[Richard buttocks]

Ok well you either have a diode issue with the alternator or most probably its just the fact its an older diesel.
Early hilux's etc are exactly the same.

[amlav]

Battery should be load tested after at least 8 to 12 hours of charging finished and sitting at ambient temperature .
Sometimes there is only a surface charge on the internal plates and it can be misleading .
No charging voltage should be under 13.6 - 13.8 Volts . (even on idle)
Never the less you could have problems with the alternator brushes/diodes/connections .
There would be an easy test to check alternator .
Fire up the car and remove very briefly the positive cable from battery.
If car keeps running than more likely alternator is ok.
Regards,
Andrei