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| Gas Tank air pressure (Page 1/1) |
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bergertime
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OCT 15, 10:02 AM
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I'm getting excess gas tank pressure, Its an 88 Gt 5-spd. Canister is good, overflow tank is good. I can NOT blow air from the line running from the gas tank expansion tank to the gas tank with the gas cap off. I've sprayed carb cleaner in the tube, I've applied 100 lbs of air pressure to the line. If I apply air pressure to the line leading to the gas tank from teh overflow line with the gas cap off, I should get air escaping from the filler neck right? Any suggestions other than dropping the tank? TIA
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olejoedad
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OCT 15, 12:28 PM
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What symptoms lead you to believe there is excess air pressure in your gas tank?
The tank is vented via the smaller diameter tube leading up to the filler pipe behind the gas door.
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fierofool
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OCT 15, 12:52 PM
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There is a valve in the very top of the tank that is attached to the metal lines of the sending unit. It's to prevent liquid from being expelled into the vent lines. I'm not sure which line that is on the 87, but it could be that the check valve is preventing the air from entering the tank.
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olejoedad
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OCT 15, 04:08 PM
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The tank would go under vacuum as the fuel level dropped.
The only time it would pressurize would be when filling the tank.
That pressure is vented via the small diameter pipe running parallel to the large diameter fill pipe.
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bergertime
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OCT 15, 09:33 PM
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Because when I take off the gas cap there is a ton of air that escapes. I can also hear the tank pop when I take off the gas cap. It a new to me fiero that had been parked for 20 years, the guy I bought it from had aleady replace the fuel pump. I thought my canister was plugged, tested it and it is fine, I tested the gas expansion tank and it's in good shape. Maybe I'm wrong but as fuel evaporates, the fumes should go from the tank, to the expansion tank and then to the charcoal canister. So should air flow freely between the gas tank and the gas expansion tank?
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olejoedad
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OCT 16, 06:36 AM
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Things to try
Check vacuum lines from engine to canister.
Check for proper operation of vacuum valves on canister.
Disconnect vent line from the fuel tank to expansion tank to see if problem goes away.
Disconnect vent line from expansion tank to charcoal canister to see if problem goes away.
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bergertime
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OCT 16, 03:21 PM
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How many vent lines does an 87-88 fuel tank have?
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fierosound
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OCT 16, 03:59 PM
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| quote | Originally posted by bergertime:
I can NOT blow air from the line running from the gas tank expansion tank to the gas tank with the gas cap off. I've sprayed carb cleaner in the tube, I've applied 100 lbs of air pressure to the line. If I apply air pressure to the line leading to the gas tank from teh overflow line with the gas cap off, I should get air escaping from the filler neck right? |
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It definitely sounds like the vent line at the tank end may be the problem.
It may have rusted internally. You will have to drop the tank.
https://www.fiero.nl/forum/...421-1-075023.html#p8------------------
My World of Wheels Winners (Click on links below)
3.4L Supercharged 87 GT and Super Duty 4 Indy #163
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bergertime
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OCT 16, 05:09 PM
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I think you're right, I just really don't want to drop the tank and was hoping there might be an alternative. Thanks.
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