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Fuel tank holding pressure

adamforsythe

adamforsythe

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If you block off the breather tube should the fuel tank hold pressure? I hooked my air compressor up to my breather tube and put some air into it to see if it would hold pressure. Air is pissing out from where my sending unit is attached to the tank.
 
Not sure, but I *think* the sending unit should seal fairly well to the tank... otherwise you wouldn't need a vent tube =))

-- A
 
FYI, the new evap system test here in Cali puts 4psi pressure in the tank and vent system, while pinching off hoses into canister, to test for leaks. F'n pain in the ass to keep from getting leaks in all that hose and crap on trucks going back as far as '76.:doah:
 
Yes it should seal. IIRC from my factory manual, the later caps are vented at 16PSI, so GM must have expected the tanks to hold quite a bit of pressure if the breather system failed.

Concern I would have would be the contaminants potentially getting into the tank, along with $4/gallon+ fuel leaking out. :)
 
Ok would this cause a starvation problem???? There are times when I'm going down the road and the engine will start to drop cylinders in tell I put it in N or park. Then I'll have to wait a little bit (5-10 sec) before going again Carb is fine, fuel pump/filter are new and in good working order. I'm thinking that since there is NO pressure in the tank (other then fuel) it is screwing with my fuel system....is this possible?
 
If a fuel tank isn't able to vent properly the tank can implode (suck inwards) and fuel delivery could be a problem.
 
I understand that but if a tank does not hold any pressure not ever 1 psi will that cause a problem????? Because my engine started running funky after I changed out the sending unit. I know the sending unit didn't seal right and it will not let the tank to build up any pressure.

4X4HIGH said:
If a fuel tank isn't able to vent properly the tank can implode (suck inwards) and fuel delivery could be a problem.
Click to expand...
 
The fuel tank should vent freely and not build any pressure unless it's hot outside and you get low on fuel. That is usually when you'll notice pressure in the tank.
 
Well what might be happening is when the truck is low on fuel it might not be building up enough pressure to run fuel through the lines.
I guess I'll find out tomorrow.:crazy:
4X4HIGH said:
The fuel tank should vent freely and not build any pressure unless it's hot outside and you get low on fuel. That is usually when you'll notice pressure in the tank.
Click to expand...
 
The tank DOES NOT need pressure in it (and shouldn't have any) for the fuel pump to deliver it to the engine. The whole reason for the tank being vented either through a vented gas cap or a charchoal cannister is to prevent the tank from pressurizing.
 
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