subtank wiring oem 100 series style.

[semlin]

i'll try this over here since it crosses over to an 80 series pretty closely. looking for comments and answers to the questions below (if you have the patience to read)

i have been researching how to wire and plumb a subtank in the factory manner for a 100. that means the dash subtank switch toggles between tanks. there is no transfer between tanks. my understanding is some 80 gasser subtanks were also wired this way along with many diesels.

below is my plan to do this "near oem". with a couple of connector changes this would also work on an 80 since the harness point i am tapping in is in the same location.

for a 100 series going full oem is impossible or at least impractical unless your harness/ecu is subtank ready. the oem install includes separate relays in the rear quarter panel for the sub fuel pump and the solenoid that are controlled by the ecu. in fact, there may even be a separate fuel control computer for some models although it shows up in the 1999 uzj oz epc as "not applicable".

anyway, here is the swap plan

1. disconnect the main fuel line and return line from the main tank behind the tank. these parts are fully compatible with the subtank harness. you join the subtank line assembly in series into these parts.

2. install the oem fuel line-solenoid 77720-60070 for 100 series subtank vehicles. this is a "t" solenoid that switches line flow between the two tanks, apparently on the return line.

3. install the oem y pipe for subtank vehicles on other line (appears to be main fuel line) 77205-6A060

4. connect everything either with proper factory lines or flexible fuel line.

4. install the oem 100 series subtank stub wiring harness 82414-60010. this will reach from the subtank fuelpump/sender and the solenoid up into the rear quarter panel. in the oem configuration it would connect there to a relay for the solenoid and a relay for the sub tank fuel pump. for reasons explained below i think neither is needed.

5. make up a harness that interrupts the main fuel tank stub harness at the connector under the driver's side passenger door sill and also connects to the sub tank sub harness and the subtank dash switch.

to do this you need

-harness wire
-male and female connectors to match the main tank harness stub plug
-connector to match the subtank harness stub plug
-connector for subtank switch
-a single pole double throw (spdt) relay (oem part suggestion welcomed)

the harness is then rigged as follows

-12v power for both pumps comes from main tank fuel pump relay at all times so the ecu does not know of the existence of the second tank. this power goes to the spdt relay which is controlled by the subtank switch. think of it as a parasitic system.

the subtank switch operates the relay which toggles the factory main fuel tank harness from the ecu side to feed either tank, so it switches three things
a) main tank fuel pump and subtank fuel pump
b) fuel line solenoid position "main" or "sub"
c) fuel line sender wires from main and sub

this will mean pressing the subtank button switches tanks and switches the dash fuel gauge to the active tank.

This leaves a few unknowns

-do i need a momentary overlap of power from both fuel pumps when switching? it looks as if the factory system has an open y where the fuel lines join. as long as the power switch is instantaneous i think that the fuel pressure regulator and the volume of fuel in the fuel filter will cover for me.

-do i need a separate power source and relay for the fuel line solenoid or can i piggy back it off the fuel pump relay using just one spdt relay? the factory setup includes a small efi style relay for the subtank fuel pump (oem parts are 90987-02004/85999-12050) and a larger relay for the solenoid 28380-50020. i do not need these to control these devices. i also assume i do not need these for voltage drop since the main tank fuel pump is powered from engine bay to middle of the rear by a 14 gauge wire (i will use 12 gauge wire to run power down to the subtank stub harness). however, perhaps i should find a separate power source for the solenoid and rig two spdt relays from the subtank switch.

-in the oem setup the oz websites indicate the ecu will redirect the return line fuel on shut off to the subtank so it gets the dregs and does not become completely empty. i will lose this function. not sure how important it is to tank function. i cannot figure out how to wire something that temporarily switches to the subtank position (if necessary) then switches back.

-there is probably a function that auto-switches tank if you ignore the "e" light and empty a tank. i think i can live without this.

-i need a dash light that tells me when the subtank is live and the fuel gauge is reading the subtank sender. first step is to look and see if there is an unused light position in the instrument panel, hopefully near the fuel gauge. if not, then the easiest solution is likely drilling the sub switch for a light .

 

[george_tlc]

Seems like a lot of work versus a transfer pump

cheers,
george.

 

[semlin]

that's very debatable as i've seen the wiring splices for a transfer pump plus on a 100 if you go with a transfer pump you will be rigging two switches in the dash.

 

[george_tlc]

If done by someone with reasonable wiring skills, a transfer pump setup is quite simple. On my 80 the transfer stop automatically when the subtank is empty. Factory 80 subtank installed with my own little control circuit/module that takes the factory subtank switch as control.

If you have your monkey wiring things up, then he'll have even more chance of making a mess with dual pumps, relays, switches, harness splicing etc

Anyhow, I can't see the value in doubling up all the fuel pump/return hoses etc etc. If one is really worried about the one high pressure fuel pump failing out in the sticks, just take along a spare.

I've had my transfer pump based subtank installed in our 80 for at least 12 years now and it works well and reliably with minimum fuss. Given the subtank size, I didn't even bother with a gauge since I just transfer the lot when down around 1/4 full on the main.

cheers,
george.

 

[semlin]

If done by someone with reasonable wiring skills, a transfer pump setup is quite simple. On my 80 the transfer stop automatically when the subtank is empty. Factory 80 subtank installed with my own little control circuit/module that takes the factory subtank switch as control.

If you have your monkey wiring things up, then he'll have even more chance of making a mess with dual pumps, relays, switches, harness splicing etc

Anyhow, I can't see the value in doubling up all the fuel pump/return hoses etc etc. If one is really worried about the one high pressure fuel pump failing out in the sticks, just take along a spare.

I've had my transfer pump based subtank installed in our 80 for at least 12 years now and it works well and reliably with minimum fuss. Given the subtank size, I didn't even bother with a gauge since I just transfer the lot when down around 1/4 full on the main.

cheers,
george.

i have no issue with a transfer system, but i don't agree it is simpler or better than what i am describing for a 100. as i see it, the wiring and plumbing is not more complex. it is just a different way to go. if i am missing something technically i am all ears.

an oem 100 subtank is already plumbed with its own fuel pump, and with its own main line and return line. all i am adding is the "t" for both lines into the main line system, and an equivalent "t" on the wiring to select tanks.

there is also a minor advantage in what i am proposing. it can be done with a single dash switch on a 100 instead of two. if i use a transfer system i will need a switch to control the transfer pump and a switch to toggle the fuel gauge.

 

[george_tlc]

Well, have fun with it. I guess you should move this thread back to the 100 series then j/k

Maybe someone else that has done a dual high pressure fuel pump setup can offer some suggestions, though I think most folk in the 80 forum that have done subtanks have gone with the factory 80 scheme of a transfer pump.

cheers,
george.

 

[semlin]

I think most folk in the 80 forum that have done subtanks have gone with the factory 80 scheme of a transfer pump.

i have done some reading on oz forums and there were 80s that came with the tank selection system. according to posts there it is seemingly random which system is used. it may be there are port or dealer installed tanks there that create confusion.

 

[george_tlc]

No - in Oz there are no "port install" options. The diesel 80's definitely had a dual tank suck/return scheme, but that works easily since the fuel pump is NOT in the tank. So, they had a solenoid that switched the suck and return lines from the main to the sub.

I've not heard of a petrol based 80 subtank system that was NOT transfer pump based stock from toyota. AFAIK ALL petrol 80's in oz had the subtank - since the assumption was that a) the average aussie can deal with the dual filler and the subtank switch and b) you would be dead in the oz bush if relying only on the piddly stock fuel tank capacity

cheers,
george.

 

[semlin]

No - in Oz there are no "port install" options. The diesel 80's definitely had a dual tank suck/return scheme, but that works easily since the fuel pump is NOT in the tank. So, they had a solenoid that switched the suck and return lines from the main to the sub.

I've not heard of a petrol based 80 subtank system that was NOT transfer pump based stock from toyota. AFAIK ALL petrol 80's in oz had the subtank - since the assumption was that a) the average aussie can deal with the dual filler and the subtank switch and b) you would be dead in the oz bush if relying only on the piddly stock fuel tank capacity

cheers,
george.

i have no idea other than i have read otherwise. i did try going over the epcs. numerous 80s and 70s have t solenoids and single external fuel pumps but that could indicate either set up. i have yet to find one with its own fuel pump in the subtank which is what the 100 has.

 

[george_tlc]

I'll just say that the Gregory's (Australian after market manual) ONLY shows a subtank transfer pump scheme. When I did my subtank install, talking to an 80's guru in oz, ONLY the transfer pump scheme was mentioned for 80's. Also, the US 80's have the harness in place for the subtank, it is only a transfer scheme.

I would say it is highly likely that the reports you've read about a suck/return from main or subtank is DIESEL specific.

So, until proven otherwise - photos and/or a toyota manual saying otherwise, I don't think any petrol 80's had a dual suck/return scheme from the factory.

cheers,
george.

 

[Tapage]

I wonder if you could make your life easier using an external inline pump .. since in 80 diesel the IP it's who suck diesel from main or sub tank as solenoid just change between 'em ..

and on a note I don't know any gasser 80 with factory sub tank that use the same system as we ( I ) have in our TD 80 ..

 

[semlin]

not proof, but the discussion i was referencing. looks like early poverty pack fj80s had switchable tanks, and then there is a guy claiming it is very inconsistent on all models but he may be talking about aftermarket installs.

http://www.4wdaction.com.au/forum/viewtopic.php?f=7&t=18030

 

[george_tlc]

Bunch of opinions by a mob of yobbo aussies and a mix of diesel talk thrown in for good luck. All the talk of using "whatever was in the parts bin" sounds like a load of b/s.

Show me a factory manual that describes anything but a transfer scheme from the subtank to main and then I'll believe. Specifically for a petrol 80 with fuel injection.

cheers,
george.

 

[semlin]

I wonder if you could make your life easier using an external inline pump .. since in 80 diesel the IP it's who suck diesel from main or sub tank as solenoid just change between 'em ..

and on a note I don't know any gasser 80 with factory sub tank that use the same system as we ( I ) have in our TD 80 ..

i am going to stick with the fuel pumps that are installed with both tanks. i know those will generate the correct fuel flow rate and they will respond to the ecu flow rate adjustments.

 

[86tuning]

i am going to stick with the fuel pumps that are installed with both tanks. i know those will generate the correct fuel flow rate and they will respond to the ecu flow rate adjustments.

You can use that fuel pump to transfer fuel to the main tank still. It will work fine for that.

 

[MoCoNative]

Semlin, did you ever do this. I'm liking this plan myself, got my eye on a 105 tank with internal pump.