Thread: Electrical woes '96 Disco V8

Al, did You check all ground lines?
In TDI Discos the (-) goes from the battery direct in the chassis, and there is another cable between startes and chassis. Sometimes I hear that mechanics put a direct line between them, and then alternator, tacho and/or temp gauge electrical gremlins dissapear...

Good luck
Regards

Thanks very much for your help, it got me thinking so measured between the alternator and the battery earth and found +.5 volts the differance.
I put a earth strap between them.
still did not fix it, so started mucking around with the alternator. The new reg was differant from the old and i could not fit the capacitor next to the reg. so i did not put it in when i changed all those months ago.
I thought that it may have been built in.
So i thought i will just try and make the capacitor fit in. A bit of twisting made it fit
and when put back together the problem was cured!!!!!!
But...... I dont know what caused it in the first place as both alternators had capacitors. Also i swapped out regs and capacitors to start with and tested ok then. I really dont care now as it is working. Thank you, German Gruner for your reply as it helped get on the right track.

Oh i forgot i think maybe the problem may have been a faulty capicitor as the are used to smooth out ac ripple in this application as that which may come from an alternator. when load is switched in or out it may start voltage occillation up or down, so the signal going to the cpu causes the excitation voltage to swing like pushing a child on a swing, until it fails. I assume that the signal from the alternator needs to be a fairly pure dc voltage. This would explain the intermintant action of the tachometer. Then the failure of the voltage control would make sense. But i still cannot work out why i did not pick this up earlier.

Far out ..Man

That's a lot of thought that's gone into the solutions

Personally tho ... Using a Alternator that came off a motor that been crushed by a tree would not have been my choice

Mike

Some thoughts...

If you were having such dramatic variation in voltage, it suggests to me that the regulator is NQR. You can have two problems at once, but it's usually a case of one before the other, possibly causing the other.

The entire electical system should run off the alternator, not the battery. With everything on you should still have a voltage at the battery HIGHER than the float voltage of the battery without engine running.

The tach signal is not rectified. It comes off one of the field coils only.

Originally Posted by MacMan

Some thoughts...

If you were having such dramatic variation in voltage, it suggests to me that the regulator is NQR. You can have two problems at once, but it's usually a case of one before the other, possibly causing the other.

The entire electical system should run off the alternator, not the battery. With everything on you should still have a voltage at the battery HIGHER than the float voltage of the battery without engine running.

The tach signal is not rectified. It comes off one of the field coils only.

Hello
I wish i had better electrical diagrams at the time to help me work out how the reg works and other stuff. I have now reread my last post and understand maybe i did not explain my self well. " I was thinking that maybe because the voltage was fluctuating so much it was upsetting the electronics supplying the regulator." Now that you have told me that the Tacho is not rectified. I wonder whether the absence of a capacitor allowed a rogue AC ripple to overlay what should have been a clean variable AC signal.

It still appears to be fixed as i am running 600 watts of headlights (have a lot of wildlife where i live, wombats, roos and cattle) as well as all other circuits without missing a beat! I am very happy is an understatement!!!!!!
p.s I changed out the regulator fairly early on in the problems with a new one ordered thru the local auto elec. At this stage i still have in service. So i thought i had cured the issue of the reg. I still really do not know what caused it nor can i really say with a definitave answer how i fixed it other than about 90% sure it was the capacitor help cure the issue
Cheers alturbo68

Originally Posted by mike 90 RR

Far out ..Man

That's a lot of thought that's gone into the solutions

Personally tho ... Using a Alternator that came off a motor that been crushed by a tree would not have been my choice

Mike

hi
I will post a photo of the wreck soon, I hit the tree really hard and the airbags failed to go off, the srs light was up on the dash for about 2 weeks before and i thought "I must find out what that means". Well i did and it meant "the airbags aint gunna work" lol!!!! .
So lesson learnt there! Seriously though i was fortunate that the motor was still able to run, and i drove it up onto a trailer. That motor is the new heart in my current disco. All the chassis is pushed sideways and broke an engine mount.
If i hit that tree in a Holden "common dore", a Fraud "falcon" or other such car, i would be pretty messed up.

The Disco's are pretty strong and i am happy to own one
Cheers alturbo68

"That which can be done with fewer assumptions is done in vain with more."

I think you've over thought all of this.

You are overlooking the fact that your battery is the biggest and best capacitor that can be had, so to me it points the finger back at the alternator. Just because it's a different one does not mean that it is bad. Yhe only way you can test it is to take it to an auto electrician and have them spin it up on a growler. Until you KNOW that it is capable of delivering adequate voltage and current you're making a very large assumption that I would not be making.