Fuel pump noise - ‘72 280SE 4.5

[Achim]

Hi all,

I have the impression that my fuel pump is starting to make a louder noise, I can hear it over the engine noise while driving slowly, which I don’t think was the case a few weeks ago. It’s fairly quite after a cold start but seems to get louder as I drive (or the car idles for 5 min). I have recently replaced all fuel hoses in the engine bay, but still need to replace the ones in the the back of the car.

I will replace the fuel filter and look for obstructions in the fuel lines, but I wonder if it is time to look for a new fuel pump? My biggest concern is a sudden failure of the pump leaving me stranded.

I have seen numerous posts about this topic, but any pointers are welcome.

For what’s worth, here is a link to a video showing the noise (it comes across louder in the video than it is in real live, hopefully the short video comes across): Noisy fuel pump

[Diesel911]

Kind of out of my league on this part of the Forum. I had to look up that it is an electric fuel pump and I found this that has some suggestions on what other pumps could be used: https://www.benzworld.org/threads/1972-280se-fuel-pump-needs-replacing.1688609/

Not trying to be negative buy I was wondering how many people actually know what a 1972 fuel pump sounds like when it running normally?

[Tomguy]

I know my 4.5's pump was loud. I don't recall how loud but you could hear it running inside at idle. I can't tell how loud yours is on the video but if it's getting louder (I don't recall getting louder as it warmed), it could be a few things, such as pressure in the tank, bad fuel filter, bad tank strainer, etc.

[Idle]

Liquid pumps make noise for several reasons and all of them are easy to check.

Now most of this applies to any electric pump. The disassembly stuff below applies to the vertical pumps used for a few years and not the later types used on the 107 and 116 cars. I am guessing you still have the original pump.

If you are sucking air you will hear a sound like a lot of small pops. This is called cavatavion and will eat up the inside of your pump. If you check your hoses from the tank and they are sound then it is unlikely you are sucking air.

There can be a vibration. Just check the rubber isolaters that hold the lower pump bracket to the top one. I think there are three of them. They get old, crack, break and cause a lot of vibration. There is also a rubber ring around your pump to cut down vibration. Maybe it is cracked and part of it is gone?

There can be trash in the pump area. This is a bigger deal since you have to remove the pump and unscrew the bottom plate off. You will be amazed at how dirty is is in there. You could just be hearing friction from the impeller hitting the trash that has built up over the years. It will not look like much but then it does not take much. Clearances are tight in there but no so much that it is a precision job requiring special tools.

Worse case: Bad bearings in the pump. This would require a total rebuild. Not impossible but a real hassle. It is sort of like rebuilding a smog modified carburetor: Lots of stuff to keep up with and it all has to be right. But it can be done if you do it slowly and carefully.

You will know if it is bad bearings when you get the bottom plate off and you find a lot of resistance in turing the impeller by hand. It should move with some resistance but not a binding amount.