VDJ79 Sub Tank Not Switching Over (5 Viewers)

[SneekyPete]

Hi Everyone,

I have a VDJ79 single cab which has started not switching over to the sub tank. The light on the dash changes over, but the solenoids don't change over and the engine never draws fuel from the sub.

I can't find any wiring diagrams anywhere on this vehicle. I've had the dash apart and it looks like the sub tank switch goes into the factory wiring loom so I'm guessing is factory Toyota.

I've chased the wiring back to where it goes between the top of the main tank and the underside of the body and it all looks good, I'm just not getting any power.

Can anyone point me in the right direction for where I should look? Is there a factory relay location that I should be checking?

Cheers,

Pete

 

[coldtaco]

Did you locate the switching relay? Find it then have someone push the button to switch and while they do that listen/feel for the switch to move. Most likely it’s the switching valve. Or unplug it and put 12v to each tab with and see it it moves. If it does then your problem is somewhere between the switching valve and the switch

 

[SneekyPete]

Did you locate the switching relay? Find it then have someone push the button to switch and while they do that listen/feel for the switch to move. Most likely it’s the switching valve. Or unplug it and put 12v to each tab with and see it it moves. If it does then your problem is somewhere between the switching valve and the switch

I've not been able to find the relay. I don't have any manuals for the vehicle so I'm unsure where the relay would be and chasing the wires from the switch isn't really an option as the 4 wires from the switch go into the wiring harness.

My only other option that I can see is to drop the main tank out and finish chasing the wires back from the solenoids into the cab/engine bay.

 

[scottmk1]

Hi SneekyPete, if you PM me you email address I'll send some wiring diagrams over.

 

[fl4031003]

I could use the wiring diagram too, please. Sending you a PM

 

[coldtaco]

The switching valve is near the front tank mounted on the inside of the frame. As to where specifically for your VDJ I don’t know since we don’t get those here yet, too new. Just follow the fuel lines from the engine back. I think there will be two, one for feed one for return.

 

[OGBeno]

Get a subscription to the Toyota OZ tech website and download whatever you want.

 

[rick_d]

Pete. Please post if you find the relay to complete this thread.

 

[rick_d]

there is a common relay 90987-02027 which updates to 90080-87026 in US. Four pin blue unit that may be in kick panel fuse box.

this is all a kind of guess.

 

[rick_d]

I replaced the relay in 2011 hzj79 single cab and this location for relay fixed the switching valve issue.

 

[John Young]

On a somewhat related issue, I've looked in the FSMs but cannot seem to find a comprehensive fuel diagram and I've got a bit of an issue with Golden Boy:

This is a photo after about 24 hours parked with a slightly nose up attitude. Drips appear to be coming from both sides of the rear tank.

Golden Boy is a 1991 HZJ75. The guys in Dubai swore they fixed the fuel switch system but now when I press for the sub tank the light in the little binnacle just flashes erratically. The front tank fuel gauge works to an extent--It shows a quarter tank when the front tank is completely full. I've been driving the truck quite a bit and had noticed that when the tail is lower than the nose it did drip just a little bit, but not as much as this. Yesterday I filled up the front tank to top (which I should not have done), figuring that the issue was only with the rear tank. The drips are definitely only from the rear tank and it seems to be dripping from both the right and the left side.

What I don't get is how the fuel is getting from the front tank to the rear tank. I think the rear tank should be pretty empty by now. I can't seem to find anything in either the 70 series body FSM or the engine FSM that is very useful. I get that the injection pump continually sends fuel back to the tank, but why is going to the back tank?

I've been meaning to dig into this, but I am leaving for a couple of months. I'm trying an experiment by putting the truck in a slightly nose down attitude to see if that makes a difference.

I'd really rather not fiddle with this before I leave. Thank goodness it is only diesel and not gas. I probably will go out and get a fuel siphon tomorrow and try to drain the rear tank at least.

I'd really appreciate any thoughts or advice the forum might have for me.

 

[coldtaco]

first off, you should have two tank switching valves, one for fuel to engine, one for fuel returning to the tank. When you are running off of the front tank, the fuel return should go to the front tank. If running off of the rear tank then the return should be to the rear tank. At least that is my understanding of how this works. When you remove the fuel caps is there pressure with both or one of them? Does the rear tank level indicate empty? I am guessing that one, the level gauge for the rear doesn't work right, and second, the return switching valve is not working and it is stuck with the return to the rear, therefore overflowing. Just a thought.

 

[John Young]

The good news is that the leak almost completely disappears if the truck is parked slightly nose down:

I'm just going to have to drop at least the rear tank. But I won't be able to do that for a couple of months. Sigh.

 

[SneekyPete]

Thanks everyone for your help. It was indeed just the relay that was no good. Replaced and now all is working correctly