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Old 11-27-2018, 10:51 AM   #1
Captain J
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Post Fuel leak

Greetings
What causes fuel to pour out of the tank filler neck after starting the engine.
I’ve a 1986 GMC Sierra C2500 that I swapped the engine to LS with auto transmission, factory dual fuel tanks, factory fuel sending units, finished 1 year ago, but never used the truck due to issues with the conversion.
It was stored for about 4 months, but it ran ok when it came from the workshop.
I fixed some wiring and I started it yesterday, it started ok, but I noticed fuel started pouring out from the left tank filler neck, it feels the tank is pressurized. Shut down the engine, disconnected the battery, but fuel kept pouring for about 5 minuets.
Anyone know why? Causes? Solutions?
Thanks
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 11-27-2018, 10:55 AM   #2
Palf70Step
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Re: Fuel leak

Never heard of that. I would try to remove gas cap and see if it still happens. If it dosent, I would replace cap. Also, you can try disconnecting the vent line at the canister under the engine to see if that is causing tyhe pressure to not release. My guess though is the gas cap.
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Old 11-27-2018, 11:57 AM   #3
Dead Parrot
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Re: Fuel leak

Somehow fuel from right tank being returned to the left tank? Check for hoses crossed at valve. Possible valve has internal failure.

Might try switching tank switch to other side and see if problem swaps sides.
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Old 11-27-2018, 01:06 PM   #4
Captain J
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Re: Fuel leak

Quote:
Originally Posted by Palf70Step View Post
Never heard of that. I would try to remove gas cap and see if it still happens. If it dosent, I would replace cap. Also, you can try disconnecting the vent line at the canister under the engine to see if that is causing tyhe pressure to not release. My guess though is the gas cap.
The gas cap was off,
I’m not sure if there is canister, but I’ll check
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 11-27-2018, 01:08 PM   #5
Captain J
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Re: Fuel leak

Quote:
Originally Posted by Dead Parrot View Post
Somehow fuel from right tank being returned to the left tank? Check for hoses crossed at valve. Possible valve has internal failure.

Might try switching tank switch to other side and see if problem swaps sides.
The fuel switch not working, the fuel valve is new, but I’ll recheck it.
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 11-27-2018, 01:09 PM   #6
Killer Bee
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Re: Fuel leak

Quote:
Originally Posted by Dead Parrot View Post
Somehow fuel from right tank being returned to the left tank? Check for hoses crossed at valve. Possible valve has internal failure.

Might try switching tank switch to other side and see if problem swaps sides.
bingo! not uncommon issue with multiple possible culprits..

good luck!
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