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Old 01-08-2004, 09:36 PM   #1
stimpy
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Join Date: Jun 2000
Location: Austin, TX
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2008 STI

Exclamation Fuel tank function help

I can hardly fill up my car due to the auto shutoff activating

I took the time to install a 1999 Forester fuel tank into my 1996 L. This was done because my 1996 was missing some of the sensors present on a WRX. However, some of the pieces were disconnected and the FSMs did not really help me much (atleast the pages I was looking at during that time). After some creative engineering, I got the plumbing worked out to where some of the stuff was bypassed and some of the stuff was used.

On my old gas tank, there was a 1/2" hose that went from the top of the gastank up to the fuel filler neck. As best as I can figure, it's purpose was to allow the displaced air somewhere to go. In trying to duplicate that same scenario with my newer filler neck, I have run into a problem. I went ahead and took the 3/16" fittings and attached a hose to them hoping to duplicate the scenario. So now there is a fitting on the top of the fuel tank connected to the fitting at the top of the fuel filler neck just like on my old tank. However, when I attempt to fill up the tank I find the fuel shutoff kicking on almost immediately. I am assuming that this is caused by the air not escaping fast enough and causing the gas to back up the fuel filler neck.

At present, I have bypassed the charcoal canister by attaching a fitting to the vent valve and running it directly back into the evap system. In looking at the mechanical function section of the FSM, the vent valve opens when the tank pressure begins to build and it then vents the excess pressure into the charcoal canister. What confuses me is that is looks like there is no larger valve for the displaced air to pass through; it merely pushes back into the small 3/16" evap system. That leaves the question: how does the displaced air move out of the way and allow one to fill their tank at the high setting?

-Jon
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Old 09-24-2004, 09:15 PM   #2
stimpy
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I'm not going to detail everything wrong with what I did, but the FSM provides an excellent resource for exactly what should be happening and where all the air and fuel travels. This can be found in the Mechanism and Function Section.

-Jon
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Old 09-25-2004, 11:07 AM   #3
Legacy777
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Jon,

Are the new tanks different then older tanks? Does the new filler neck not have this vent on the side of it like the old ones?

Here's a pic of the old style filler neck
http://www.main.experiencetherave.co...4/DCP_3108.JPG

There also should be a fuel separator that was present....at least it was there on the older models. It hooks up to the two small vent lines on the tank. Those lines go to the fuel separator, which is just a sealed plastic container. A third line comes out and goes to the charcoal canister.
http://www.main.experiencetherave.co...4/DCP_3109.JPG

The canister purge solenoid doesn't open via pressure, it opens when the ecu tells it to, which is when rpm is above a certain point for a certain amount of time.
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Old 09-27-2004, 12:41 PM   #4
stimpy
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The tank gains a couple gallons in the newer cars, the emissions system was moved from the engine back to the back of the car, the roll-over valve was relocated between the drain valves and the fuel filler neck, additional sensors and valves were added, and numerous hoses changed sizes.

I don't even know how to describe the exact path of everything other than suggesting looking at the mechanism and function sections of the FSM. You cannot see where all the hoses run, but there are numerous conceptual views of where things go.

-Jon
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Old 09-27-2004, 02:14 PM   #5
Legacy777
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AWD 6MT EJ22T AWIC Swap

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by chance do you have any scans from a newer fsm? I've mainly got the older ones.
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