over volting issues

[abens21]

hi i have a 1997 legnum v6tt and i have been having issues like driving back from cairns the lights were coming on then the alternator shat it and battery exploded managed to get towed back to the sunshine coast broke down in Gladstone 500km away got the alternator rebuilt and put it all back in and was putting out 18v at idle and new battery and smoking so i stopped and put a second hand one in and doing the exactly the same thing had them both tested and putting out 14.5 v on the test bench so i was wondering if anyone has any ideas to what it could be thanks so much

[wintertidenz]

So the alternator is showing 14.5v on the bench, but 18v in the car?

[abens21]

yes both of them say 14.5 on bench and in the car go crazy

[wintertidenz]

I'd check all the fuses, especially the big ones for the alternator.

It could also be an ECU issue, but check fuses first.

[abens21]

yeah checked all fuses car starts and runs fine and drives ok with alternator out no issues but as soon as it in over volts yeah im a bit worried as it died on me doing 100 down the highway and locked up and threw me off the road because alt died and batterey exploded replaced all the alt fuses with everthing on puts ut 13.5 volts all off goes to 18 and reving it about 18.5 so yeah goes crazy

[swinks]

voltage regulator faulty ?

[Davezj]

i would have gone for the voltage regulator as well.
i believe it sits on the back of the alterantor, so i would have assumed that it would have replaced with alternator.

the test to say if it definitely the alternator/regulator would be to disconnect the alterator from the battery then start the car and the battery voltage should be 11V-12V ish and going down slowly as the engine uses up the available current in the battery.
just make sure everything else electrical is turned off in the car as you do this.
if you do test this and get the result i metion above, then it can only be the alternator or the voltage regulator. if you have seen the alternator running at 14.5V then you can draw you own conclusion that it is the voltage regulator.

big ICE installs can do some odd things to the electrical system of the car when you do it wrong.
maybe you have something on the car that damages the voltage regulator almost instantly when you fit a new alternator, and then after that, you are just killing the battery with 18.5V

[abens21]

yeah got a new everything new reg and everything um even got another alternator out of another legnum and tested before install in the car 14.5 at idle and in mine 18 if i turn everything on like lights ac and that goes down to 14 and i took them both in to a shop after being in car and they both still do 14.5 on the machine they basically saidd cut the computer wires the 2 end ones on the wiring and yeah give that ago i didnt really want to cut yet just looking to see if anyone had this issue car is completly standard everything jdm head unit nothing has been changed

[exevoowner]

Check all earthing cables and cables to alternator also main cable to starter if there is a short anywere will cause regulator to put out more than needed i had this and was only found after close inspection of cables

[abens21]

yeah checked everything could find issue, spoke to a auto eleckie and they said to unhook computer control wire and done that and volts 13.5-14.5 and works fine no issues he thinks may be a computer issue or some as computer trying to over volt

[Davezj]

there is a earth wire that sometimes gets missed off when putting stuff back together.

there should a braided earth wire between the accelerator cable mounting point on the plenum chanmber and the fire wall/bulkhead. this needs to be connected as it is the main earth from engine to chassis.
i am not sure it would make this particular issue occur if it is not connected but it is comon for this cable to get missed off. worth checking.

[swinks]

there should a braided earth wire between the accelerator cable mounting point on the plenum chanmber and the fire wall/bulkhead. this needs to be connected as it is the main earth from engine to chassis.

I thought that battery earth cable is bolted to chassis, just below fuse box :)

[Davezj]

yes the battery GND is connected to the chassis at that point, but the engine earth wire is the braided one at the back of the engine. which is also the earth path for alternate, i believe it is the only factory fitted earth strap to the engine from the chassis.
many people have got earthing kits fitted which add extra earth paths back to the battery from the engine and other body panels, but the factory earth for the engine is only one.

[Z-Kev]

if the computer wire is disconnected and the voltage stays at 13.5-14.5, try a quick reloom, just that one wire , if the problem is still there its your ecu , if it goes it is a looming issue

[swinks]

but the factory earth for the engine is only one.

Dave, look at electric wiring manual, chapter 3-21 onwards ;)
That earth cable you mentioned is not the only one.
There is one going from underneath cooling thermostat housing to chassis under fuse box ;)

[Nick Mann]

Yep, I agree. The braided one that attaches to the throttle cable mount at the plenum is the second engine to earth path. The earth strap from the battery to the chassis continues on from the chassis to the bellhousing.

[Davezj]

Really, thanks for the info this is a new one on me.
I must check mine, I believe that the only connection from battery chassis to engine on my car is the the after market earthing kit that was fitted by the previous owner.
Maybe he removed the old earthing wires from my car.

Where dose the original wire attach to on the bell housing?
So I can check mine.

[Nick Mann]

At the top. Slightly forwards of middle. It is the cable with a black cover and a yellow stripe.

[Davezj]

I will have a look for it.
I have other earth wires going to the engine and gear box. But I will for completeness.

Thank for the info nick.

[abens21]

where would i get another ecu from? lol would wiring in a aftermarket stero in cause this issues as well

[wintertidenz]

I'd remove the stereo and see if it helps. Otherwise there are some ECUs around the place for sale.

[Davezj]

i checked my car i can't seem to find the factor eathing cable to the bell housing so mine must have been removed when the aftermarket earthing kit was fitted, probably due to the after market stuff being red and the factory one being black.

[Mr.Salas]

Hey guys,

I know that this thread is old, but i am having a semi same problem. My alternator was working fine until one of the pins in the voltage regulator connector broke due to rust. So I removed the alternator and send it to a repair shop to replace the voltage regulator. After I received the alternator back and installed it, it came to my notice that when the car is cold the voltage would be 14.4V and when the car gets warmed up it drops to 12.5V. So I when to the repair shop again to replace the "faulty regulator" and after installing the alternator back in the car and tested it. Well the alternator voltage and behavior stayed the same 14.4V when colt and 12.5V when warm. So, when I went to the repair shop, the owner told me that this isnt the first time they have experience this with a mitsubishi alternator. He said that the aftermarket LM314 voltage regulators for some reason isnt compatible with the ECU of the car and that I should buy a original voltage regulator from Mitsubishi. So, I went to the mitsubishi dealer and requested a quote for the voltage regulator.. well very expensive my friends USD350 for the regulator only.

So, my conclusion is that the aftermarket voltage regulators aren't compatible with our ECU's for some reason.

I was looking at the wiring diagram and I think im going to do some test, such as cutting the wires from the ECU to the voltage regulator or cutting the battery voltage sensing wire that goes from the alternator to the regulator.

Lets see how things go, if this will help because, when I turn on my AC and the lights the voltage drops to 11.7Volts, which is below battery voltage , big NO NO.

Will update you guys later.


So the moral is : when ur alternator dies, just buy a used or new one.!!

[swinks]

Voltage 13.7v to 14.4v when idle on hot engine is within norm brackets. Anything lower than 13.2v idle hot engine means something is wrong.

[Mr.Salas]

Thanks for the Info Swinks.

Well I did some cutting and measurements.
From what I can conclude is that the aftermarket voltage regulator are not compatible with our ecu. I think this would be due to the IC used(different factor) on the voltage regulator.
So, what I did was cut the voltage regulator Enable cable (black/red) cable. By cutting this cable the alternator will work OK, lets put it that way. It is not a perfect fix, but it will work until I buy another alternator.
Voltage during idle is 14.4 V, with lights on it will stay at 14.4V, but when the lights are on and you put ur AC also on, voltage will drop to 12.7 V. With brake paddle pressed, voltage drops to 12.2 Volts. It is still above battery voltage, but as soon you press a little gas, you will get 14 volts again.

By cutting both ECU cables, the voltage will be 14.4 V, but with lights and AC on it will drop to 11.7 volts.
So, in any case someone gets this problem just cut the black cable labeled as "voltage regulator enabler" on the ECU pinout chart.