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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #1 · (Edited)
So you've got an early OBD1 scooby with the 12 gallon tank and you think to yourself "Hmm... 15 gallons sure would be nice". Or you think "Hmm... My tank is leaking, but my buddy is parting out a WRX". Then this DIY is for you!

Now I'm not gonna lie, it's a pain to do. Gas getting everywhere, dropping the exhaust, driveshaft, rear subframe, etc. is not for the light hearted. I have 4 days planned for this endeavor (along with a 4.11 swap because I need a new trans, and a rear disk conversion). If I were just doing the fuel tank, you could *probably* do it in a weekend if you were working hard.

I'm not going to list out every tool you need, but a well-equipped garage is needed. There's no specialty tools, but your standard assortment of sockets and screwdrivers and pliers. Along with a set of jack stands, and a jack to support the fuel tank and subframe as you remove them.

I'm also going to assume that you can get as far as dropping the tank on your own. Here's a VERY quick and probably incomplete list of things you need to do to get to having the tank on the floor:

Remove exhaust
Remove driveshaft
Remove brake lines
Remove e-brake lines
Disconnect trailing links (from the hub, if you try to disconnect the front of them, you might end up spinning the nuts that are inside the chassis. Still don't know how I'm going to fix that one)
Drop rear subframe
Disconnect fuel lines
Disconnect fuel tank electrical stuff
Disconnect charcoal canister? (mine is old old, so I don't have the new style canister in back)
Put jack under tank
Disconnect tank straps
Drop tank while pulling the electrical connection off (The other *right* way to do this is to disconnect the plug in the interior of the car, push the grommet through the hole, and then just let the wiring drop with the tank, but either way works fine)

Ok, so you've got the tank on the floor. Now the fun begins!



The following pictures are for reference of where certain things go on the stock tank. That way when you take yours apart and forget how it all looked, you can look here.

Stock OBD1 evap (sucks air from the top of the tank, from those 2 jobbers, through the tubing, and then to one of the 3 lines that goes to the front of teh car on the strut tower:



Stock line routing,

Return is on top
Feed is in the middle
EVAP is on the bottom



Closeup of what I mean when I say top/middle/bottom. Note that I looped the return line because if you just let it drain, it'll actually siphon gas out of teh fuel tank.



Look at teh comparison!



I wonder where the extra three gallons come from?



Passengers side height difference (AKA how to tell a 12 gallon tank from a 15 gallon tank)



OMG STi partz! (for stock STi line routing)



STi jet pump and sub-sender for fuel level



STi EVAP routing, note that it exits near the fuel filler, but it is basically the same system that's on the old car:



A solenoid, and the STi tank vent:



STi fuel sending unit, from left to right the lines are:

Fuel Feed - Left
Fuel Return - Center
Jet pump dump - Right



STi Fuel pump, with internal fuel filter!



STi tank internal baffling:



STi sender on teh top, 1995 L sender on the bottom. Notice how TINY the STi fuel pump is!



STi on the left, L fuel pump on the right



A WILD SUPRA FUEL PUMP APPEARS!



STi sender vs the L sender. You CANNOT just swap the L float onto teh STi unit, as it's located on the opposite side:



WIRING:
The STi fuel level sender locates on different pins than the stock one. It also has what I assume to be a fuel temp sensor, but could be a sensor to tell if it's running E85. Either way it's different. What I ended up doing was just re-pinning the STi connector to the L pins, and removing the excess sensor.

STi on top, L on bottom:



The fuel senders themselves are exactly the same, as far as form factor is concerned. EXCEPT that they're not. The STi one is mounted "upside down" on the stalk.

Now I DID take ohm readings of teh 2 senders.

The L is at about 5 ohms when "full" and roughly 100 ohms when "empty"
The STi is at 1 ohm when "full" and 51 ohms at "empty"
The STi sub sender was at 41 ohms, and was mostly empty, but I didn't take it apart to do a full sweep.

What this tells us is that yes, you do in fact need to run them in series (the ohm values add when in series). And don't forget to repin the sender to the correct pins. What I will do is to cut the wire on the chassis, and add some leads across to the other sender. Shouldn't be too hard to do, and I'll add pictures when I do it (I hope).



You can see, even the wiring is the same:



And that brings us to the next part: the vent valve.

The vent valve is there to make it so that when you fill your tank, and offset all the air in the tank with fuel, you dont' get air trying to come up the fill tube and making bubbles and whatnot.

However, on the STi this is controlled by the emissions system. Which we wont' have anymore. You need to "gut" the valve, so that instead of staying closed, it stays open. I should also note (since I didnt' take a picture of this) that the stock L tank actually just has a hose into nothing, no valve or anything.

Here's what you need to remove from teh tank:



The bottom is held on with little clips, just push in on them and work your way around to all four, and the bottom pops off:



After the spring pops out, you can remove the plunger with the seal:



Then reinstall the valve, with no plunger, seal, spring or bottom. You'll notice that I looped the 2 open connections on teh tank to close them off. I also left the tube off of the top of the valve. The top tube is left open to atmos. because frankly it doesn't do anything, and the gas tank is still sealed off by the diaphragm.



As far as the EVAP lines go, I simply took the lines off of teh old tank, and put them on the new one. Everything lined up just about right. I've also blocked off the nipple next to the fill tube.:



For what it's worth NEVER DO THIS:



Those push connectors are a different style than the old one. Simply putting hose clams on is not up to "code" as it were. The stock ones have raised nipples to lock the hose clamp into place, the push connectors do NOT. This is pretty dangerous because the hoses *could* just slip right off.

That being said, I like to live dangerously, and don't have a better option right now. The "right" way to do it would be to either convert over to push style, or braze the old tubes onto the new sender.

So that's it for now. I'll update more tomorrow with wiring. But the basics are all up there.

1. Move old evap lines to new tank
2. Gut the vent
3. wire the senders in series
4. change fuel straps
5. figure out fuel lines

and that's most of it!

Later.
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #4 ·
WIRING TIME!

Ok, so chop off the plug on the STi sub-sender, and solder on some extentions. Don't forget the heat shrink! And the electrical tape, if need be. Cut the extentions long enough to reach over to where the fuel sender plug is at, plus about 4".

I HIGHLY recommend finding some sort of connector, so that if you have to drop the tank in the future, you can disconnect this easily. I happened to have a few plugs from an old wiring harness that fit together, but you're on your own for sourcing a weatherproof plug.

Solder/Heat shrink the plug onto the other end of the wires. You should now have this assembly:



Great! But where to plug it in?



This is the 4-wire plug that plugs into the fuel sender. The 2 thick wires are for the fuel pump, the 2 thin wires (Green, black) are for the fuel level! Here's your wiring diagram:



Notice how the "turbo" model simply wires the sub sender in series? Good. Because that's what we're gonna do.



Go ahead and snip either one of the small wires. I prefer the Green because then you don't have to worry about "which black one?". Wire your plug inbetween, solder/heat shrink. And feel free to tape it all up too.

Now the fun part!

Install your tank! You will need to buy STi fuel tank straps. I have a feeling that the passnegers side would have worked for either tank, but the drivers side definately wont. I may post part numbers later. They're only $35 a piece.



and plug in your wiring!



And then finish it up by connecting your fuel filler (I used a custom hose, because the stock hose won't fit on the STi's bigger fill hole. I believe it was 1 5/8" from autozone). Also hook up your fuel filler vacuum line. Then hook up your fuel lines and evap line.

And, hopefully, you should be good to go as far as the gas tank is concerned.


I'll let you know if it's right when I start my car next time. God only knows when that's gonna be.
 

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'MURRICA!
Hybrid Camry
Joined
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5,700 Posts
Discussion Starter · #6 ·
This is the STi assembly, but there are 2 problems:

1. the 12 gallon tank doesn't have a sub-sender, so there's that
2. the STi tank wiring is on different pins than the L is. Which forces the previously mentioned re-pinning.

Using the STi assembly without adding in the sub sender would make your gas gauge only work halfway. So when it reads a half tank, you'd be empty. The STi senders operate on a 0-50 ohm range of resistance each (which when wired in series adds the resistance, and gives you a 0-100). The stock L sender is just 0-100 ohms.
 

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1995 WRX 2015 F150
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1,873 Posts
From what I remember doing mine, you need to break out all the plastic inside that white valve. You only removed the roll over valve. The tank still won't fill.
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #8 ·
We shall see.

Airflow is good though. And the anti-reversion valve is still in place in the stock L filler neck FWIW (It's a dual-plastic-flapper-valve located inside the actual neck, where it connects to the tank)
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #10 ·
Still haven't started the car yet, but I did turn the key to "on" and fuel did come out of the pressure line, so things are looking good.

And my gas gauge read half a tank, so I'm guessing that's correct too (there was about a half a tank in there).
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #12 ·
Ok, it's been started! It runs! So I know my fuel pump is hooked up correctly.

The only worry was that after it was idling for a bit the gas gauge (which has always been SUPER slow to respond) dropped down to "E". So I decided that some fresh fuel was just what the doctor ordered to test not only the filling, but also the fuel gauge. Here's what I found:



WORKS PERFECTLY

There were no issues filling the tank at all. It worked just like normal. Didn't stop early at all. It did stop when the tank was full.

Fuel guage before:



Fuel gauge after:



So yes, my wiring works correctly! :D

Thus endeth the DIY.
 

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04 GDB 2.5RS
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This would explain why my fuel gauge reads 1/2 full when it is empty after swapping an STi tank into my legacy :( at least I don't have to drop the tank to fix it lol
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #15 ·
Month after update: Everything is still working as it should. Fuel pump is good. Fuel gauge is good. Fuel filling is still good! :D
 

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Just an FYI on my new gas tank for the fuel pump sender side I switched pins 2 and 5 and it worked like a charm, tank reads perfectly now. :) Wish I had seen this thread a few months ago. Thanks Cory!!
 

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07 Civic SI / 97 Miata M
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757 Posts
Bump for this. I was wondering what to do with the emission stuff and the wiring.

Thanks. What year is your STI tank?
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #18 ·
Not 100% sure, but I think it's an 04 or 05 tank.
 

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07 Civic SI / 97 Miata M
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Not 100% sure, but I think it's an 04 or 05 tank.
I'm about to update to upload some pics. I need some assistance. Give me a minute.

Alright, mine is definitley from a 2005 and is complete. I pulled it off the wrecked car a few years ago.

Here you can see where you had an open nipple is. I have some kind of mechanism.

Got the thing apart. Easy enough.

Copied your hose to open nipple conundrum


As you can see from the first picture I have some extra wiring. I am assuming I discard all that crap and its all related to emissions?
 

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'MURRICA!
Hybrid Camry
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5,700 Posts
Discussion Starter · #20 ·
Yeah, I didn't use any of that wiring harness. In fact it's still sitting in my garage along with the evap lines :lol:
 
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