Fuel Problems

My 1995 Dodge Ram 1500 runs great as long as I don’t allow the fuel tank to drop below 3/4 full. After that the engine will shutter and shake and begin to lose power, putting me on the roadside. So far I have learned to carry a small 2-gallon gas can in the bed of the truck in case I am not near a gas station when this happens.

I have reason to believe that there is something wrong inside the fuel tank that is restricting the suction of new fuel into the fuel pump’s pickup tube. However, I am baffeled as to why this only happens when the tank is less that 3/4 full. Anyone have any ideas?

The symtoms you describe could be from a weak fuel pump. Have a fuel pressure/leak-down test performed to determine if the fuel pressure is within spec.


It sure sounds like a classic fuel pump problem.

I bet if you park on a hill, headed down, you will be able to get by with a half tank. Just don’t try driving back up the hill.

There is also the possibilty that there is a lot of rust and other crud in your gas tank that gunks up the fuel sock, making it difficult for the pump to suck up the fuel unless you have a full tank. The fuel pump and fuel sock may be parts of a single unit, so replacing one unit changes both components. But be sure to also clean out the gas tank.

Don’t ignore the possibility that your gas tank may not be venting. You may be drawing a vacuum in the tank, which may be overpowering the ability of the fuel pump to deliver. Not sure if your Dodge has a venting cap or a venting tube.

I agree that it sounds like a vacuum being drawn in the airspace. The tank breaths in as the fluid level drops through an activated charcoal bed in a charcoal canister under the hood. If the bed is saturated, which can in some vehicles be caused by “topping off”, then the tank cannot breath in and a vacuum develops as the fluid gets pumped out, preventing the pump from pumping. Uncorrected this can also cause preamture pump failure.

The next time this occurs, try removing and reinstalling the gas cap. If you hear a whooshing sound that the problem disappears, you’ve successfully diagnosed the problem.

Post back with the results.