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New to forum and e21 scene. Just was delivered my 77 320i. Excited to get to tune and drive. I have a really loud buzzing sound coming from fuel pump. The line between accumulator and fuel pump vibrates and makes alot of noise. I have replaced fuel relay, fuel pump, fuel filter and fuel filter and noise is exactly the same as all old parts. The line from accumulator to pump looks new and there are no restrictions in line. What would be the next step to figuring out what is causing the noise?

Are you able to narrow down what is the source? Perhaps caused by the accumulator indeed? The whole kit it inside the metal bracket (see image below) and hanging from a set of bushes (nr 4 on photo)? All parts are hanging freely, not touching the bottom of the car apart from the fuel hoses? Did you also check under the cover that is located under the rear seat? You could for example have a hose clamp rattling against the top of the fuel tank just as well.

My next step is replacing or cleaning fuel level sender. Well that's what Wallloth and Nesch calls it. Manual calls it a booster pump. The one in tank. Hopefully that fixes problem. Its a really ridiculously loud buzzing sound.

Since that is only a pick up that can hardly be the cause imo

I thought so too that's why I didn't replace since noise was only from pump to accumulator line. I ordered all lines and fuel level sender. I'll replace all drain tanks and see if problem solved.

Just a suggestion,
Are you shure the mounting assembly with pump and filter is mounted with the 3 rubber silent blocks (item 4 in the sketch) to the car bottom?
If the assembly is mounted directly to the bottom of the car the fuelpump noise would be transmitted through the car bottom, and would be loud indeed.

Yes the rubber mounts holding everything together is there. The noise is only coming from the hose line from pump to accumulator. Basically the line on top of accumulator in pic going to pump on right of picture. The line is vibrating like it is struggling to work. Car drives fine around the block.

Think I figured it out. Fuel gauge was half full but tank was empty. Filled up gas tank and sound from pump is half the sound it was. Gonna try cleaning fuel level sender to see if that fixes fuel level.

Fingers crossed!

Update. Still waiting for parts I ordered 2 weeks ago. But I found a screw loose on voltage regulator, found a replacement at hardware store. No sound at all from fuel pump. Seems to have fixed alot of other issues also. 44 cents solved at least 4 problems! Still replacing fuel level sender when parts ever get here. Looks like my car was updated at some point with booster pump and sender. Glad I looked closely before ordering 77 actual intank part. Completely different. Having fun working and fixing problems on this car.

Especially fun if you're getting somewhere!

The fuel pumps on these cars sometimes buzz. I have had two 320i's. One of them had a buzz and my current one doesn't. I remember my parents brand new 1979 320i had a buzz. Sometimes they buzz sometimes they don't. I think the guage is an electrical issue. Take care

Thanks. That is what I am looking into now. Going over the electrical part now Cleaned the booster pump and sender. Gauge is still off by half tank. Tank is almost full but still shuts off at half tank mark. I just ordered new sender anyway. Now buzzing only happens when it think its running low on gas. Slowly getting this back to running great. Just got my Clutch kit because of bearing noise when clutch is up. And Top End Performance exhaust system because I was driving and a hole blew through header hanger connection. Looks like someone before hit the whole exhaust off of the hangers. Two huge holes. Not sure how with the truck height suspension.

Update on my problem. So after a year of buying 4 external pumps and filters, replacing every hose and clamp, rewire of fuel system, rebuilding k jet distributor replacing injectors and replacing booster pump in tank I finally solved solution. Since I replaced intank booster pump with a high flow in tank pump I no longer needed external pump. Yesterday I decided to disconnect the external pump instead of intank pump and car is running whisper quiet in fuel area. So today I replaced external pump with braided fuel hose to accumulator. Car runs fine. I guess the high flow fuel pump is way stronger than having booster pump. Finally can move onto restoring rest of car. I have replaced every bushing and car is night and day difference in handling. Glad I stuck with this car. Lots of fun. Thanks for the help.

That clearly caused a mismatch, good to hear issue is solved now! Feel free to start a project topic in the 4 cyl section of the Owner's Gallery and keep us updated!