fuel pump going bad if you hear humming noise?
 

hello

after searching the forums, seems there's a general consensus that if your fuel pump starts making a loud humming noise, that it's on its way to failure and should be replaced.

my 1987 560SL makes this humming noise specially on really warm days, and though I thought I'd tracked the noise to the left side of the gas tank I guess it could be coming from the fuel pump which is in the right rear near the wheel. Will check that area specifically next time I hear the humming.

my question is this though, if the humming is the pump going bad, why does it not stop when the engine is stopped? On my car, it keeps up the humming, sometimes quite loud, until I go to the gas cap and open it, releasing all the built up pressure. The noise then disappears immediately.

any thoughts or explanations as to the above behavior?

thanks in advance

You may be hearing the "singing gas cap" or you have a leak in the tank system, that is "wheezing". Sniff around.

My fuel pump whines/hums periodically - not all of the time - has been doing this since I bought the car in 1997. I've read here and elsewhere that changing the fuel filter sometimes helps. I do this annually and it still whines/hums from time to time - not all of the time.

I've heard of people who've changed the fuel pump out and the whining/humming continued.

When my pump died
 

it would start humming, more when it was hot out. It progressivly got worse then it started affecting performance, mostly under high fuel usage conditions. If the AC was on it wasn't as bad (there's a fuel cooler.) When I changed them (I have two) the problem went away and I noticed one of them rattled when I shook it.

The fuel system is a constant flow system, what isn't used is returned to the tank. But if your noise goes away when you take the gas cap off it may be a seperate problem, and a cheeper problem, fuel pumps aren't cheep.

I also hear a humming / screetching sound from the rear of the car, under the back seat, only when the engine is on. Its not constant, but continuously intermittent. Is it the fuel pump - will it give me any notice before failing (like the noise getting louder)? Also, I think (not sure) that the noise is more on hotter days. Its a 190E (87).

Also keep in mind the fuel pump is cooled by fuel. If you consistently run the car with a near empty fuel tank, it'll shorten fuel pump life.

based on comments from others, thanks by the way, it might be the fuel pump or it might not....the fact that the noise continues with the engine off(and thereby the fuel pump off) kinda leads me to believe it's not the pump but am unsure.

not sure about a leak in the tank either since there's quite a bit of pressure that comes out when I take the gas cap off.

will see if anyone else chimes in with feedback/comments....rather not swap out the fuel pump if I don't have to.

It may or may not be a problem
 

The fuel pumps in my 1991 420SEL have made a humming sound since I bought the car and the car runs fine. My mechanic says there is no need to change the pumps...

The pumps in my daughter's 1989 300TE did not make any noise, whatsoever, and then suddenly one day one of the pumps failed. A few days prior to the failure, however, there was a strong smell of gasoline.

So there you go.....