1999 XJ 2.5TD charging problem

[M84AB1]

Hi guys,

I have been a long time reader of these forums but am first time poster.

As the title suggests I do have a charging issue with my car and was hoping that one of you fellow jeep owners can provide some insight.

Basically the problem I have is that the alternator only outputs 13-14 volts at higher RPM, at idle for instance it does not charge at all, the voltage sits at 12 volts or so. It behaves actually quite linearly, as the RPM go from 750 to 2500 so does the voltage from 12V to 14V.

I have tested the dashboard volts gauge and it is fairly accurate. Reads very closely to my Fluke digital multimeter, so it is definitely not the gauge that is faulty. Having said that, obviously I have tested the voltage at the battery as well as the Alternator B+ terminal with my Fluke.

I have contacted a local jeep wrecker here in Melbourne (Jeepers Beepers) and as I was calling around to see how much alternators go for. As I described my issue to the person on the phone, he straight away hinted towards the alternator itself.

He also quoted me $150 for a used alternator so before I go out and spend some of my hard earned I was hoping that somebody on here had a similar issue in the past and can provide some pointers.

[anthonygubbin]

I can not confirm if your VM has a battery temp sensor but if it does read the following linked thread. If the thread is relevant then I would start with the $1 mod first and go from there.


http://www.ausjeepoffroad.com/forum/...hlight=voltage

Regards A

[M84AB1]

Hi anthony,

According to the official service repair manual and associated electrical wiring my XJ turbo diesel should have a battery temperature sensor. However, upon removal of the battery itself, I can see the hole where the sensor is supposed to be, but there is no sensor!!!

Now I removed the battery tray to see if there was a connector underneath somewhere which would hint that the sensor was removed at some stage by the previous owner(s). But there was nothing. There is however a rather longish piece of wiring in wire loom that sits next to the battery but does not connect to anything. Maybe that is it.

In my service manual it is stated that a functioning battery temperature sensor should measure a resistance of between 9Kohm and 11Kohm. I then took a 10Kohm resistor and inserted it across the two terminals of that wire/connector that just sits there to see if it would do anything. Unfortunately it made no difference.

I was then thinking, maybe this version/year model does not come with battery temperature sensor and the reason why there is a cutout on the battery tray was because they use the same tray for all models irrespective of whether or not it has a battery temperature sensor.

[anthonygubbin]

I will try to remember to look at my diesel wreck and see if there is one on it. it is sounding like the missing sensor could be your problem. what you want to try is two 47k resistors sitting parallel which will give you around 14.2v at idle, providing your battery is in good cond.

regards a

[M84AB1]

Thanks mate that would really be great. At least it would help me establish whether or not my car is supposed to have a BTS.


I was also hoping that someone else with a functional XJ 2.5TD could take a look and report how his/her alternator behaves.

[Richard buttocks]

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

[amlav]

Have the battery load tested first . Had similar issues . Battery was at only
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.
Glow plugs drain around 25Amps from the battery when turn ignition on .
Replaced the battery and charging voltage shows ok . (around 13.6 to 14.2).
There is no battery temperature sensor on mine either .
The old battery was 4 years old .
Regards,
Andrei