Hi all, I've recently replaced the alternator in my ute (XF with EFI 250) due to the existing one not charging the battery.

From the time I installed it it would periodically overcharge the battery, I only noticed it by seeing the voltmeter on the dash jump from %25 to maximum.

I also got a new battery because the old one was failing from the lack of charge from the previous alternator, and this one is boiling over from the overcharge level..

I can be on the highway with the engine at a steady ~2000RPM or have it idling out of gear or in gear and it can be charging normally with the voltmeter displaying a steady %50 and then it will very quickly go to maximum the gauge can display.

When this happens out of gear idling the engine speed decreases slightly and increased again after it returns to normal.

The weird thing is that it just seems to randomly happen for a few seconds or up to a minute, and can sometime occur several times in the space of half an hour.


If anyone can help i'd be great, by my thinking if it was the voltage regulators failing it wouldn't be happening with such random behavior?

Don't trust the guage, it's a guide. Get a multimeter on it to check.

Trouble is I can't replicate the conditions it occurs under because its so random.. It hasn't happened just after I've just started it, usually it starts happening a few minutes after. I'll give it a go though.

I meant to run a couple of wires into the cabin tonight so i can monitor it and record peak voltages on the multimeter while driving.

Hey,

Just like the last post get a multimeter and check the charge rate on the batteries, if that comes up ok could possibly be a dodgy regulator and yes i know its a new alternator. Also make sure your earth lead isnt loose on the battery and on the body as i had it happen to my old XF where my lights were going out randomly found the wire from battery to body loose. Hope that helps

Not 100% sure about the alternators on xf's but had this problem sereral times on my xe panno, turns out the 2 small colored wires plugging into the back of the alternator weren't plugged in properly. Try unplugging them and scrubbing the fk outta the clip and the back of the alt with degreaser then lightly tapping them back on with a screwdriver or pair of pliers. They should 'click' into place from memory..