mercedes e320 fuel pump keeps failing

Hi there, I have a 97 mercedes e320. Recently the fuel pump relay went bad and the board was replaced with a new one. Also the fuel filter was replaced. The problem now is that the pump fails after just a few starts. Only thing I can think that I have done is unplugging the battery to do some checks and plugging it back.
Can this cause the pump to fail?
Any advise will be appreciated.
Joe. :S

Do you have access to any diagnostic tools, e.g. DVM, graphing voltmeter, or a oscilloscope? Having wiring diagrams would be very helpful.

You say the pump runs for a while and then stops working, but what makes it start working again? Over night? Waiting an hour? Disconnecting battery ...

I suggest ensuring that the pump circuit has current present, meaning if current is present the circuit is working.

What I'm guessing is that your pump was the reason that your relay and/or board went bad by perhaps pulling too much current.

So, when your car stops running because the pump stops working, try to thump on it. Here's how I suggest doing it. While making sure car is in park and the car isn't starting, crank the car and have someone smack on top of the fuel pump or on the gas tank in a fashion to not damage anything. You need power being sent to the pump while smacking on it, so you need to have the car cranking. If all of a sudden the pump starts and the engine runs, your fuel pump has some bad contacts in it and needs to be replaced.

I would also suggest checking powers and grounds at the pump to ensure all is good.

By the way, ScannerDanner has numerous videos on this and does a much better job of explaining this procedure.

Sounds like 20 year old fuel pump is on its' last legs without pro tools (a scope and DC amp clamp) the only real test you can do is when it cuts out check the pump is getting supplied with near battery voltage under load and has a good ground.
As already mention thumping on the base of the tank can sometimes get you home but even if that works a new pump is needed real soon.

Fuel pumps like starters, alternators and fans have carbon brushes and commutators that just wear out it has been working for two decades it is very likely just pooped. (Like Madeline Kahn in Blazing Saddles Just pooped.)

Thank you for the answers. One fact that may no be clear is that when the pump fails it is dead, no good.
It is one of those pumps that resides out of the fuel tank. I have replaced it twice. Really can't understand why it would burn or fail so quickly.
Joe.

It genuine Mercedes or Bosch pump ? the quality of replacement parts has become a major problem.
However with out of tank pumps floating debris in the fuel tank blocking the fuel suction in the tank can cause the engine to cut out. It may them clear when the engine and key is switched off for several minutes . With no suction to hold it the debris drops clear of the suction pipe filter.