Why is gasoline draining out of my charcoal canister?

295

Asked by froeschl Feb 27, 2021 at 02:38 PM about the 1981 Cadillac Fleetwood Brougham Sedan RWD

Question type: Maintenance & Repair

Today some gasoline was draining through the charcoal canister of my '81 Cadillac Fleetwood Brougham 6.0. A puddle formed below the front left (driver side) corner of the vehicle. When removing the fuel tank cap, I noticed that the tank was under negative pressure. Air was flowing into the tank when I removed the cap. Apparently there is/was a vent problem with the cap.Since the tank was almost empty, I'm just wondering how gasoline could get into the hose routed to the charcoal canister in the engine compartment. Is that related to each other?

8 Answers

38,625

something ain't right you'd better take care of that before there's a fire .

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154,565

Sounds like the purge valve is stuck open and allowing gasoline to be sucked up into the EVAP system. The negative pressure is probably normal. When I remove the gas cap from my 94 Fleetwood I can hear air rushing in the tank. My 93 Caprice used to do that too. Check for misrouted vacuum hoses too. The hose connections should be marked on top of the charcoal canister. Hope that helps! Jim

1 people found this helpful.
295

No, there may NEVER benegative pressure in the fuel tank! Seems the ventilation valve in the tank cap was stuck not allowing air to flow into the tank. I assume the negative pressure in the tank was sucking gasoline out of the carburetor via the hose connected to the charcoal/vapor canister. For my understanding there is no other way how fuel get get there. So if the tank ventilatiion works well, everything should be OK.

1 people found this helpful.
154,565

If your Fleetwood has the 6.0L V8 it's fuel injected. You don't have a carburetor. For enough gasoline to get into the charcoal canister to fill it up and cause the gas to leak out it has to be getting sucked into the canister from the gas tank. If negative pressure is never in the gas tank, what's the hissing sound I hear when I remove the gas cap from my 94 Fleetwood? Jim

1 people found this helpful.
295

Well, what I mean is that there's something wrong with the ventilation of the fuel tank in case air is rushing into it after removing the tank cap. That's an undesired condition; negative pressure in the tank is never good. Can deform and damage the tank What's not clear to me is how gasoline gan get into that hose routed to the vapor cainster, particularly when the tank is almost empty? The hose should be connected somewhere on top of the tank. It is physically not possible that fuel gets into this hose. Not even under extrem negative pressure. Only if turning the vehicle top-down :-) So the fuel in the vapor canister must be coming from somewhere else. BR Peter

154,565

If the purge valve is stuck open engine vacuum can pull gasoline from the tank into the charcoal canister. Also, if you did have excessive negative pressure in the gas tank the engine would run poorly. The fuel pump wouldn't be able to supply enough fuel to the engine. Is your check engine light on? Are you seeing a rich or lean trouble code? A problem with the purge valve will not set a trouble code on this vehicle. You pull the trouble codes from the climate control panel on this vehicle. Hope that helps! Jim

295

Jim, seems you are right. But what's your explanation how fuel can get into that rubber hose going to the vacuum canister? Actually there should be only gases/vapors going from the fuel tank to the engine via the charcoal canister. It is totally unclear to me how that can happen. Isn't the hose connected to the top of the tank? Thanks to anybody who can can clarify my doubt. Thanks, Peter.

295

I was able to figre out what was causing this issue. All fule lines were replaced at an auto repair shop in November 2020. Unfortunately they swapped the return line and the vent line to the vapor canister. When connected correctly, it is actually impossible that gasline can get into the ventline as it ends on top of the fuel tank (sending unit). Peter.

1 people found this helpful.

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