full & empty tank

[KEUDJ]

Hi,

I have a problem on my BB 440 dodge charger, when the tank is full the idle is correct, the more the tank empties the less the engine works correctly, it stalls and the idle is not stable.
all the emission control system after fuel tank vent line was removed.
after driving for a while, if i open the fuel cap, a loud suction noise occurs, I guess this is normal (also small suction noise come from vent line under the hood)
right now the engine has a stock fuel pump, i plan to replace it with an electric pump. i'm not sure if this will solve the problem
the fuel tank is the only mechanical part i did not remove when restoring the car. on the documentation i saw a complex piping system on a liquid/vapor separator near the tank. can i remove this device or will it cause another problem?

Does anyone know this problem or have any idea where it could be coming from?

Thanks

 

[dadsbee]

Sounds like you have a non vented cap on the filler when you should have a vented cap.

 

[Bird 426]

You do have the gas tank vented?

 

[WileE]

You need to vent the tank, either through the pre-emissions setup, or by the EECS on later models, depending on your vehicle.

 

[Rishi]

suction noise? hmm, could that be a poor/bad vented fuel cap?

if it were me, I would leave the vapor vent lines at the tank in the rear in place. they do good things.

when your engine misbehaves, if you vent that suction from the tank, does it run better for a while?

another topic of recent discussion on this forum is about the mechanical fuel pump pushrod. on some engines, this wears and gets shorter, and causes all kind of goofy problems in fuel delivery.

if your fuel flow from the tank to the engine gets an assist by the fullness of the tank, you may have a fuel pumping issue to resolve. the electric pump may very well solve this. I'm not fond of those, as they have a few problems of their own, but nothing significant.

if it were me, I would want to know what my (after pump) fuel pressure looks like, at a full tank when things run well, and near empty, when things run poorly. if the pressures were the same, and the fuel pushrod was up to spec, I may then give up and move over to an electric fuel pump.

 

[R413]

You can put the biggest fuel pump you can find and it won't fix it. You need a vented gas cap.

 

[j-c-c-62]

So according to the shared plumbing diagram, the tank cap is noted as pressure/vacuum relief, it is not "vented".
So, if the OP has such a cap, a question is, how much pressure/suction is needed for relief and is his cap within spec?
I am also not sure if the charcoal canister actually vents the system on its own, hence the need for relief valve gas cap, don't know. But if all the other pictured items do not exist on the vehicle, a simple vented cap is likely best choice.

 

[KEUDJ]

Hi,

Thanks all for your reply ..
when I get the car the charcaol canister and all after was removed
I plane to check preasure full & empty ... in progress
I will try winthout gas cap

I will post the results ...

 

[GTXDAN]

If the vapor liquid separator is working correctly the tank should vent through the charcoal canister to the carb. If it is not and the charcoal canister gets gas in it, it will make it run erratic. If you remove the tank vent line and carb bowl vent line from the charcoal canister you should be able to suck air through the canister purge line. If not it is plugged and will not let the tank vent properly. As j-c-c-62 said this system requires that pressure/vacuum cap for proper operation. This sounds like a Commifornia car as my 70 GTX has this on it too, only without the canister. It vents through the breather in the right valve cover that connects to the air cleaner.

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