E30 Fuel Pump Noise

[armEn30]

Hi guys,

i have a 87 325i, and recently i changed both fuel pumps. my old external pump was making a loud noise and the car used to shut off. now that i have changed both pumps, the car is perfect...but i feel like there may be another problem. when i have around 1/4 gas in the tank, the external fuel pump start making the same noise again (but not as loud), but i dont have any power delivery issues. any idea why its making that noise when its 1/4 full.
thanks

[MIKYZZ4]

I believe the pumps are both lubricated and cooled by being immersed in the gasoline,
so low fuel levels are not recommended, as that can cause early failure.

[1843lamp]

It may be an indication that your in tank ,pre fuel pump is weak or not functioning.

[Jeffnhiscars]

Both of the above are spot on.

a weak, plugged or failed internal pump causes the external to suck when it is designed solely to push.This causes cavitation which is what you are hearing. You may have rust in your tank which is a typical cause of multiple failures. I'd pull the lid under the back seat and do a visual (with obvious caution not to blow yourself up). If theres crud in there a low fuel tank will stir it up and plug the input screen on the in tank.

[thejlevie]

My first suspicion would be rust sediment in the tank. When low the sediment can be stirred cup and clog the inlet scree of the low pressure lift pump. That will starve the high pressure pump and cause it to make noise. The fix is to pull the tank, acid clean it, and seal it. A search of this subforum will turn up my procedure, which has worked every time.

[95BMWIC]

I had 2 fuel pump issues this spring with each of E30s having close to 200K. One pump completely failed (after beginning to make a loud humming noise) and the other began to make a loud humming noise (so I decided to replace before failure)

I made the mistake of purchasing a Beck Arnley brand from Rock Auto.. I installed both and when running I would get a slight humming noise (with seats installed). It was noticeable in both cars. Then one day while driving (a month later) the humming noise got real loud - similar to the loud humming noise of the original pump before failure and after 100 miles the pump seized and quit working. Pulled it out and bench tested = could not get it to run.

I then ordered 2 VDO pumps from Bavauto to correct the problems with the cheaper off brand units. No humming noise. Just a second possibility - if you didnt buy the Siemens/VDO (which I believe is the OEM) - it could be a poorly manufactured pump. It was in my case.

[armEn30]

Hey guys, thanks for all ur comments.
i noticed something yesterday.
When i was driving the car yesterday in the canyons with a full tank of gas, the car was not making any noise, but i did realize that when i was driving the car harder than usual, the outside pump would start making noise (still not loud) but it sounded like a its sucking gas out of a empty tank. but when i pulled over and stopped for few minutes, the noise was gone.
So i dont know if i should be worried or if thats a normal thing.

[thejlevie]

See post #5. It sounds exactly like rust sediment

[MIKYZZ4]

The fix is to pull the tank, acid clean it, and seal it.

The fix obviously seems to be the recommendation included in post#5.
Btw, thejlevie has more experience than myself, so I would heed his recommendation.