Factory sub tank - sourcing and fitment discussion

[grinchy]

Question I have is did you verify that the senders read in a linear fashion? Meaning does (15+410)/2 = 212.5 ohm read on the gauge as half a tank?

No, the FSM only has test points for 15 ohm and 410 ohm (with a range on each). Most pots are linear.
The Combination Meter (dash cluster) is converting to 128 bits and reads in digital, so I think it must be quite linear to support that, but of course they have the detail and could build in compensation.

 

[NY2LA]

Thanks for the kind words. I made it more difficult than it had to be, but sometimes that’s the way of finding the way.

My dream is that one day someone distills this thread down into an ordering link, parts list, and instruction pamphlet. Meanwhile, I couldn't resist one last comparison...

 

[grinchy]

I am so impressed with this whole project. Thanks for bringing us along for the ride.

Electronics scare me, so I’m not entirely sure what magic happens in this circuit. Naive question - could this be adapted to read a LRA auxiliary tank fuel level?

<edit - uh-oh. and Yes*, see further post>

This could absolutely work with the LRA sender. We just need to know the full and empty resistance on that sender, and we can work out the resistor values to use in the circuit. <Edit: 0 to 90 ohm>

The toyota sender is 15 ohm (full) to 410 ohm (empty), the voltage across is decreases with fuel level. This isn't universal, and the integration of a 'reverse' sender that decreases resistance (increases voltage) would be more difficult, but I think also achievable.

I know from the LRA video that you can buy the toyota sender and use it with their float, so there are several viable solutions here.

Edit: one big difference is that while the gauge values could be combined, you can still 'run out of fuel' if there isn't any fuel in the main tank, so the circuit might need to be enhanced to make sure there is a visible notification when there are four gallons or something in the factory tank

 

[grinchy]

My dream is that one day someone distills this thread down into an ordering link, parts list, and instruction pamphlet.

And take all the fun out of it?

Actually parts list and instructions should be in the recent posts.

Finding a filler is the biggest challenge.

 

[grinchy]

I'll likely be digging in again with my LRA and charcoal canister as I'm not sure they have it configured just right. Having some problems fueling the main tank and I suspect an issue with the open vent and charcoal canister, particularly when mixed with many dusty miles off-road.

My recollection on the Aus side LRA video is they exclude the sub tank from the evap (they route the hose from purple to green back onto itself). Is it the same for the US tank or is there an evap Tee? I don't recall it but I didn't study too deep.

Can you post up the hose routing diagram for the LRA?

Is this correct?

Evap codes and LRA aux tank

For the third time in 3 weeks, with increasing frequency (twice in 2-3 days), I’ve had the following 5 codes thrown P043E, P043F, P2401, P2402, P2419. This is an ‘18 with 21k miles, so it shouldn’t be happening. It’s highly probable it’s related to the LRA aux tank, IMO. I hate to go to the...

forum.ih8mud.com

 

[grinchy]

Fuel gauge combining for the other non factory tanks:
*all disclaimers apply, I don't have one. This is outside the use instructions, etc and so on.*

Tank 2 - Some fuel tank you have with a sender. Note that the main issue here is that paralleling resistors can't increase the resistance, only decrease it, so if your tank is more volume percent than your sender's resistance / 395, results will be increasingly inaccurate.

Tank 1 - Factory Main tank (24.5g)
Tank 2 - 12.5g LRA (example only)
For 37gal, the LRA is 33.7% of volume. The stock gauge has 15 to 410 ohm sweep (395 ohm effective). 33.7% of 395 ohm is 133 ohm.
I don't know how to scale the resistance from 0 to 90 to 0 to 133 ohm, but we can solve an approximation. We can remove 90 ohm from the main tank sender resistance, and have the LRA tank represent 23% of the gauge sweep (though it is 34% of the volume).

Parallel resistor value for LRA Sender - None
Parallel resistor value for Main tank sender (assumes 15 to 410 sender) (320 ohm effective target) - 1450 ohm
LRA sender - 90 ohm sweep. Stock sender - 320 ohm sweep. total sender resistance is 410 ohm.

General solution
Replace your aftermarket tank sender with a Toyota 15 to 410 sender, or a sender with the resistance more than the percentage of volume is to 395 ohm (a 220 sender will work for a 24 gallon tank, for example, but not for a 40gal).

 

[Toyoland66]

IMHO I wouldn't combine the gauge if running the LRA tank. It makes sense for the OEM system since the function is automatic and behaves as a single large tank, the LRA on the other hand has to be manually switched to pump into the main. Running both on a single gauge presents the risk of running the main tank dry without the gauge reading empty.

 

[grinchy]

IMHO I wouldn't combine the gauge if running the LRA tank. It makes sense for the OEM system since the function is automatic and behaves as a single large tank, the LRA on the other hand has to be manually switched to pump into the main. Running both on a single gauge presents the risk of running the main tank dry without the gauge reading empty.

Yeah, probably want to add an LED somewhere on the factory sender side that turns on then the resistance on that sender increases to 390 or something. . . not particularly hard to do with a transistor, LED, a pot, and some balancing resistors.

Or even better, when the main tank drops to a certain voltage (or increases to a certain resistance), turn on the LRA relay and transfer in fuel . . . <edit - like this - replace the 'sensor' with your fuel sender resistance, and adjust the sensitivity to profit Amazon product ASIN B01N7B8VP5>
<there are many, some for $5 each or so, just search around>

 

[afgman786]

It’s sexy?

View attachment 2615874

All this hard work you've done and you didn't bother snipping the ends of the zip ties to make it look complete before sharing the photo.

Freaking awesome job!

 

[grinchy]

All this hard work you've done and you didn't bother snipping the ends of the zip ties to make it look complete before sharing the photo.

Trailer harness still in process, not related to subtank.
But I will admit that In general, I don’t care about unsnipped cable ties .

 

[grinchy]

All this hard work you've done and you didn't bother snipping the ends of the zip ties to make it look complete before sharing the photo.

Freaking awesome job!

Looks like I was serious as a heart attack earlier. Sorry, read this message wrong.

It’s done when I say it’s done

 

[afgman786]

Looks like I was serious as a heart attack earlier. Sorry, read this message wrong.

It’s done when I say it’s done

Come on, you didn't realize all the sarcasm in my message? Lol

If no one can see the zip ties they aren't there.. so I get it.

 

[grinchy]

Took an embarrassingly long time to build a resistor network.
R1 843 ohm
R2 201 ohm
Close enough

 

[grinchy]

An immense # of resistors was $5
Included 200 ohm, had to roll the 850 from a 510 and 330 ohm in series.

MCIGICM 30 Values 1% Resistor Assortment, 600pcs 0 Ohm-1M Ohm 1/4W Metal Film Resistors Assortment: Amazon.com: Industrial & Scientific

MCIGICM 30 Values 1% Resistor Assortment, 600pcs 0 Ohm-1M Ohm 1/4W Metal Film Resistors Assortment: Amazon.com: Industrial & Scientific

www.amazon.com

 

[grinchy]

So I built my circuit with the parallel resistors flipped. Doh! After fixing that, it went together ok. Plenty of space in the kick so it doesn’t have to be small.

real world data:
Sub tank was at 411 ohm (empty)
The fuel gauge was past full before adding the resistors. I didn’t get a reading on the main tank resistance.
I put in 14.1 gallons. The reading with 22.5 gallons or so in the tanks was 3/4 after putting in the resistors. It should be 5/8 or so with 22.5 gallons.
After adding 14.1 gallons (both tanks full) the reading is well past Full.
It’s better than before, but still 1/8 tank off perfect . . .

 

[Toyoland66]

Your success has me rethinking how I will do mine, I was planning on running a switch to switch between senders. But, just like the automatic simplicity of the fuel system I think that your solution for the gauge is the way to go. I’m gonna wait till my parts show up so I can confirm the resistance of the senders, but my plan now is to parallel each sender with a 400 ohm resister and then run the two in series. Alternately, have you seen the fuel sender converters that are programmable? That could be another option if the gauge doesn’t read accurately enough.

this is the one I was looking at it’s just hard to know how reliable it would be:

MeterMatch Fuel Gauge Interface Module

Tanks, Inc. manufactures fuel system components and polyethylene, steel and stainless steel gas tanks for street rods and special interest vehicles.

www.tanksinc.com

knowing that your gauge still reads full even though your senders are sending ~29 ohms is reassuring, because you know that your resistance with both tanks at empty is even closer to the factory spec.

 

[grinchy]

Your success has me rethinking how I will do mine, I was planning on running a switch to switch between senders. But, just like the automatic simplicity of the fuel system I think that your solution for the gauge is the way to go. I’m gonna wait till my parts show up so I can confirm the resistance of the senders, but my plan now is to parallel each sender with a 400 ohm resister and then run the two in series. Alternately, have you seen the fuel sender converters that are programmable? That could be another option if the gauge doesn’t read accurately enough.

this is the one I was looking at it’s just hard to know how reliable it would be:

MeterMatch Fuel Gauge Interface Module

Tanks, Inc. manufactures fuel system components and polyethylene, steel and stainless steel gas tanks for street rods and special interest vehicles.

www.tanksinc.com

knowing that your gauge still reads full even though your senders are sending ~29 ohms is reassuring, because you know that your resistance with both tanks at empty is even closer to the factory spec.

I did do some searching for a converter, but I couldn’t get it to be very linear with the volume mismatch going straight series and only having four or five set points. And it was $70+.
I think your series plan sounds pretty good and will likely work perfect. Particularly since you can after the fact identify actual volumes at each gauge point and keep that handy if you ever need to do a range evaluation.
I plan to run it down to 1/2, do a fill, and then again from 1/4,.I’m also considering Measuring resinstance at those points and then I can rebuild the resistors network and have it measure perfect.
it is surprisingly easy to pull the kick and undo The two bolts on the body connectors to get to the main tank pins.

my one regret with the resistors is I didn’t put them on disconnects, so I have to rebuild the whole thing to change resistance.

 

[grinchy]

I finally found a resource on the evap system in the 200 series. Sadly it’s a 90 minute video. . . It does have a few excellent nuggets in it, and I’m pretty hopeful that we can arm ourselves with field implementable fixes to f
get out of limp and suspension disable situations.

 

[grinchy]

put the engine covers back on. Looks like the test fit was before I had but the canister air filter in front of the radiator.
Tin snips quickly cut out a slot for the hose and good to go

still no evap codes . Everything running as expected.

 

[grinchy]

Found on youtube the original (aussie version) of LRA install video from 7 years ago. It has the same filler that I tried to retrofit as standard equipment. Rather than do the body lift, they suggest bending the vent tube more inline to get the factory filler out (in a later step they cut this off, so it works in that install fine to bend it, as it is later cut off). That is good to know! At least we now know that to fit that version (the ROW spec filler, with or without sub tank bung), it would require the body lift or a modification to the vent tube angle. There is NO jenga jenga jenga that will fit it thru the clearances.

Bending the vent tube, particularly with a appropriate support, may be a viable alternative to the body lift . . .

I leave it to the next adopter to try