The day was early for fully electronic vehicles, and some of the bugs had yet to be worked out. The 1980s and 1990s without a doubt represented one of the most incredible periods of advancement in automotive history, particularly in the realm of electronics and controls for the same. But vehicles of this era weren't known for their stellar reliability, partly for that reason. Case in point: some of the older, Bosch turbine-style fuel pumps like those used in the 1997 Mercedes C280.
The C280's fuel pump is much like any other turbine-style pump of the same era, and has the same problem that a lot of them did. It was during this era of computer controls that most manufacturers, including Mercedes, switched from the older positive-displacement gerotor, or rotor cell-type pumps, to the Bosch turbine. Even back in the 1980s, these submersible, high-rpm turbine pumps had a known problem: Because they relied on the gasoline itself to act as a coolant for the motor and fuel impeller, running low on gas or running out would cause the pump to overheat and fail prematurely.
Generally speaking, a fuel pump like this will fail in fits and starts, and you'll notice it first during periods of highest demand -- aka, full-throttle acceleration. It will likely manifest first as a slight bog or hesitation when you go from light throttle to full throttle. When the pump motor gets weak because of failing bearings or windings, it won't provide enough power to give the car that instant boost of pressure it needs when the motor starts pulling fuel. Afterward, the car will regularly buck and hesitate under acceleration, then under cruise, and finally at idle. Eventually, the motor simply won't supply the fuel pressure needed to fuel the engine under any circumstances.
The fuel pump can fail in two distinct ways, and they can produce different symptoms. The little impeller that pushes fuel through to the engine can wear out and leak, particularly after periods of overheating. Impeller failure is usually a little more subtle than motor failure, since the system will gain and lose pressure more gradually, and the car won't buck and hesitate as noticeably. The previous cause is possibility, but impeller failure could manifest as a net loss in power under acceleration, or even slow power surging as the computer adjusts to an unsteady fuel supply. Eventually, the pump will just spin and whine without providing enough pressure to fuel the engine at anything over idle.
In turbine-style pumps of this period, pump motor failures are usually the result of having run the gas tank chronically low on fuel; that's why most mechanics who work on cars of this era recommend keeping at least a quarter-tank of fuel in the vehicle at all times. Impeller failure is generally more acute, the result of simply having run the car out of gas, or nearly out of gas, one too many times. As soon as the pump starts pulling air, the impeller loses its lubrication and the destruction begins. It's possible to kill a pump after one incident of running out of fuel if you don't shut the ignition key off and pull over before the engine completely dies, or run the pump dry by repeatedly cranking the engine.
