Car seems to be out of gas unless 1/2 or more gas in tank!

Two years ago I bought my dream car (used) a 2002 Mercedes benz c 240. A couple of months ago the car cuts out while I’m driving! No service lights of any kind are on. Had it towed to the repair shop where it starts on the first key turn! Repair shop says ‘without warning lights’ he couldn’t diagnose the problem…the car continue to go dead without warning. Eventually I realize it cuts out when the gas gauge is at 1/4 tank. As recommended I had the Crank Position Sensor replaced the very next day it goes dead when the gas gauge is at 1/2 tank. Luckily I’m able to pull into a gas station–on a hunch I fill the tank and guess what…it starts and I drove 40 miles home without any problems!!! What’s that about??? Anyone please help?

Sounds like a failing fuel pump.

Typical weak fuel pump. You can have the one you have pressure and volume tested to make sure.

It could also be a clogged (saturated) charcoal bed or kinked vent line.

As gas is pumped out your gas tank breaths in air through the charcoal bed in the canister under the hood. If it’s unable to do this due to the bed being saturated or a kinked line, it’ll develop a vacuum that will make it difficult for the pump to maintain line pressure. As the gas level gets lower, the vacuum gets higher and the pump has more difficulty. Filling the gas tank relieves the vacuum and the car runs normally again. Yes, uncorrected this strains the pump and can lead to premature failure.

A saturated charcoal bed can be caused in some vehicles by overfilling (topping off) the tank. Yours may be one.

Fuel pumps for your car are a little involved. What you have depends on the date of manufacture (the VIN). For any 2002, I think the fuel pump is in the right gas tank and it includes the fuel level sensor as a single assembly, and it is not cheap.

Definitely have the fuel pressure and flow volume checked at the engine.

If you can hear air rushing into the tank when you pull off the gas cap, have the vapor control system checked out.

Thx Guys! I have been doing some research on line and of course ‘fuel pump failure’ keeps popping up. …Been hoping it’s something less expensive. Your comments give me some other things to have checked before resorting to replacing the fuel pump… (In the meantime, I’m keeping my fuel tank above 3/4 tank at all times!