LJ78 Charging Issue

prockport

New Member
Joined
Dec 23, 2020
Messages
4
Country Flag
united_states
I purchased an 1991 LJ78 Prado turbodiesel about two months ago. It was originally import from Australia. Long story short, the battery is going dead after about a days worth of driving and 5-7 starts.

I have replaced one of the two batteries. But both charge just fine when I put them on a trickle charger. So the problem appears to be in the charging system.

I have also had the vehicle with a mechanic who rebuilt the alternator and replaced several connectors in the charging system and returned it to me just two days ago telling me he had solved it. It died again last night.

Has anyone run into a similar situation? Or have experience with the LJ78 turbo diesel? Or this charging system?
 

Tractionman

Well-Known Member
Joined
Oct 11, 2013
Messages
1,045
Country Flag
england
It is generally considered good practice with twin battery systems, to replace both of the same make and capacity at the same time. This because if the 'old' battery has a fault, like dead cell/s, it will drag the new one down, and that could be what is happening in your case. Voltage is not everything when it comes to starting,
amps is what the engine needs to turn it, so although your old battery is showing ample volts, that is not the whole criteria. If this is the case with your old battery not having the 'grunt and is dragging your new one down, you may not have enough volts or amps available to start. Have you tried jump starting from another known good source, if it starts, that may give you the answer.
 

karl2000

Well-Known Member
Supporter
Joined
Apr 27, 2020
Messages
478
Country Flag
great_britain
Good advice from Tractionman.

Quick check, whats the voltage on your battery terminals when the engine is running?

Just to check I understand, are you saying that you drive it, start/stop it a few times, then immediately after that it refuses to start?

Or is there some time (overnight?) in between you using the truck and then failing to start? Just wondering if there could be a parasitic draw if it dies overnight.
 

prockport

New Member
Joined
Dec 23, 2020
Messages
4
Country Flag
united_states
Tractionman, I have jumped started the vehicle. that is always how I get home after it dies. But, when I have had to do that, the vehicle always barely has the power to run itself after that. No power to climb hills, headlights super dim like it is starving for power. Home is at the top of a hill and it barely makes it up the hill and when I have left it idling t open the garage, it will almost always stall.

Karl2000, no time overnight. It dies at the end of a day of driving.

Did a voltage check today. Both batteries were fully charged. Before starting, both were around 12.6 volts. Once I started it, the front battery dropped to 12.2 but the other one went to 14.55, I assume as it was receiving power from the alternator. I turned on lights, the heating fan and it dropped to 14.46.

When I turn the car off, the voltage reading front battery that had dropped to 12.2 will start slowly climbing and the one that was 14.55 will immediately drop to somewhere around 13.6 and slowly go down until the two are in equillibrium.

There is battery isolator in this vehicle, though I am not sure its purpose as I had thought the dual battery system in diesels was deliberately done in parallel for increased amperage. Pic attached.
 

Attachments

  • IMG_2721.JPG
    IMG_2721.JPG
    399.7 KB · Views: 11
Don't like the adverts?  Click here to remove them

karl2000

Well-Known Member
Supporter
Joined
Apr 27, 2020
Messages
478
Country Flag
great_britain
Thanks for that.

What's the history of it - especially around the alternator and battery isolator?

When did it last all work?
 

karl2000

Well-Known Member
Supporter
Joined
Apr 27, 2020
Messages
478
Country Flag
great_britain
Can you do us a better picture showing both batteries and their wiring? Which one goes to the starter?

Do you have an aux/leisure battery setup in there powering a fridge or something?
 

prockport

New Member
Joined
Dec 23, 2020
Messages
4
Country Flag
united_states
Thanks for that.

What's the history of it - especially around the alternator and battery isolator?

When did it last all work?


Not sure the history as I bought it this way about 2 months ago and the problem started immediately.

But I did have the alternator rebuilt as part of the last mechanics attempt to fix this issue.

I am pretty sure this vehicle doesn't need the isolator, it was added likely to run some accessories in the past. Looking on the parts list on megazip, it looks like it was originally wired in parallel.

It is generally considered good practice with twin battery systems, to replace both of the same make and capacity at the same time....
Tractionman does the scenario I described sound to you like it could still be a battery mismatch issue?
 

Tractionman

Well-Known Member
Joined
Oct 11, 2013
Messages
1,045
Country Flag
england
Hi mate, now other factors have come to light, I wouldn't think so. There is something more to this as more comes to light. Karl has asked some good questions.
The first picture looks nothing like my stock 78. Where you have what looks like an isolator and an inverter, there appears more room and standard wiring/ relays etc appear to be missing/different there.
Until seeing more, I can only speculate. As far as I know, lj78s came with the winter pack, i.e. twin batteries,
heated filter housing etc. Some 70 series only came with one battery and owners converted to 2.
The position of that one battery looks wrong compared to mine, can't see 2nd one, or where wiring goes.
The isolator has main and auxillary connections, maybe someone has one battery for starting and one aux.for camp accessories, fridge, extra lighting, and/or through what I think looks like an inverter to supply 12v converted to 240v for mains power in camp, If I am thinking as Karl, maybe this is wired wrong, your aux battery is being charged and the main starter battery is not, so once you use a full charge there, it wont start until you re recharge again. There could be a change over switch, maybe in the rear if used for camping.As your mechanic has been trying to sort I would think he has more idea what is going on here. IMHO, inherited electrical mods, are a PITA unless fully documented/explained how they work, and personally with those problems I would have it all out and revert to stock, which works from the factory.
All of the above suggestions/solutions are in the main, based on assumptions with info seen/supplied, and my limited knowledge.
We may get a bigger picture with any more pictures of battery wiring and info supplied. Cheers.
 

Tractionman

Well-Known Member
Joined
Oct 11, 2013
Messages
1,045
Country Flag
england
You are right there, never seen one.
In that case then, is that where your power drain is. If that anti rust box of tricks is drawing power to electrically charge the metal, to 'prevent' rust, whatever amount that power draw is, its coming from your battery/s. Assuming that its on 24/7, otherwise there would be no point in having an on/off power supply to something like that, whenever your 78 is parked, the device is still drawing power from the battery/s with no charge until lc is running again. With that running and power draw every time it's started, and if there is that possibility of wiring to each battery wrong, that could be your problem.
All possibilities, but no concrete evidence. Could you disconnect that to check maybe ?
 
Top