1999 XJ 2.5TD charging problem

[Richard buttocks]

yeah, dont do that.
Thats the worst advice ive seen on here in a while.

As for no charge rate being under 13.6v, i guess you've never worked on late model cars that can drop the "charge rate" to battery voltage if the load on the battery is very low.
And please go find me a 2.4 diesel hilux that charges at idle...


Where are you located m84ab1?

[M84AB1]

Thanks for your input guys. According to my service repair manual, the actual alternator output voltage is "externally" controlled, by the ECU (Engine Control Unit) to be precise. So it is definitely more sophisticated than one of my older cars that I used to have that would constantly put out 14.2V no matter what. This is what says in the manual under Operation (see attachment)

I am located in Melbourne!

[Richard buttocks]

Originally Posted by M84AB1

Thanks for your input guys. According to my service repair manual, the actual alternator output voltage is "externally" controlled, by the ECU (Engine Control Unit) to be precise. So it is definitely more sophisticated than one of my older cars that I used to have that would constantly put out 14.2V no matter what. This is what says in the manual under Operation (see attachment)

I am located in Melbourne!

petrol xj's are also computer controlled.
maybe a good idea to get an auto elec to test the alternator of you are that worried about it.

[M84AB1]

What is an auto elec?

Here is what I am thinking, if an alternator was to fail (worn brushes, bad diode, bad regulator), it would either produce no voltage at all (worn brushes) or too little/high of a voltage (diodes or regulator).

I therefore think

1. The PCM is programmed in such a way to intelligently determine when to engage the 2nd rotor and start generation. This would be the best case scenario as it would imply that the car operates as intended and perhaps my battery has lost its ability to store charge and depletes within a few days

2. Perhaps some condition within the alternator is no longer how it should be and the PCM is "misjudging" when to energize the second rotor

3. Worn (on their way out) brushes that somehow require higher RPM to make contact. i am guessing here

Richard, the fact that you made me aware of Hilux models that also do not generate a voltage/charge current at idle is somewhat good news id say. This is why I still think that the best way to know for sure is to either try another alternator (which I do not have) or have someone with the same car, state how their car behaves.

[Richard buttocks]

Auto electrician?

Second rotor?
Umm what?

[Richard buttocks]

Sometimes, when only 1 diode fails
We see a charge rate that is slightly low and with higher rpm it gets slightly better
Can be confusing at times.

[M84AB1]

Sometimes, when only 1 diode fails
We see a charge rate that is slightly low and with higher rpm it gets slightly better
Can be confusing at times.

All good mate, I know my electrics/electronics.

Yeah that could definitely be the case too. If 1 or two diodes were faulty the average rectified voltage would drop which then like you said could "offset" the trigger point of the PCM Voltage control circuit.

Too bad that these alternators, according to the manual are not serviceable. Was pretty easy repairing my old alternator when the brushes went.