Avar928

This is for an early '86 928S 32V Auto.

First things first, I replaced my original fuel pump last year since it was buzzing very loudly that I could hear it over road noise inside the cabin. Never had this issue before ever. I bought a genuine Bosch 69471 which is a direct replacement for 92860810401 and the noise went away. Happy driving and only beautiful V8 as music to my ears.

Unfortunately the annoying buzzing came back two days ago, and only after less than 1,000mi on the new pump. Granted I didn't change the filter this time around which was done within the past decade. A week before I almost ran the car down to empty so I'm thinking perhaps varnish and crap of almost 30 years inside the tank may be clogging up a filter or screen somewhere causing the pump to work harder than it should. The noise started and got louder the more I ran the car that day so it was very well likely running hot. I've read a bunch of threads already about pump noise and I already know that in my situation this is not normal.

Questions:

I'm considering doing a fuel refresher of the tank, lines, filter, and all fuel related items back there to hopefully fix this problem because I can't live with the insane buzzing. I'll be following Dwayne's guide which should be very similar.

Should I remove the in-tank pump/fuel filter and replace with a mesh as well? EDIT: No in-tank pump on my year.
Other areas to look at to address possible source?
Do I have to replace the pump again?
Best way to clean the tank?

bureau13

I don't think you have an in-tank pump in '86

Avar928

Been reading more threads clarifying that, I think they started with the in-tanks MY88+ so I should be good. The in-tank filter likely needs replacing. Looking for the best way to clean the tank.

ROG100

Your in-tank screen could be disintegrating with chunks getting into the main pump or impeding flow and causing the main pump to cavitate.
Remove the sender unit on top of the tank and check with a flashlight.

jwillman

I had a lot of noise translating into my car. Replaced the rubber isolators and noise is gone. Test pump by pulling from mount and jumping relay with the pump hanging by fuel lines to confirm the pump itself is not the source.

Avar928

Roger, how much do new in-tank filters cost?

ROG100

My price is $70.26 and the gasket is $6.45.

Petza914

I'm new to 928 ownership and have an older model ('79 K-Jet) so I'm not sure if this would apply to your '86 or not, but just this week, I took mine to my Indie for what seemed like a loud buzzing from the fuel pump. Initially, he thought it was a failure of the in-tank pump that was causing the primary pump to cavitate and make that noise, but upon checking both pumps, they were both good and what turned out to be making the noise was the Fuel Distribuotor. He replaced or Rebuilt that (receipt shows Fuel Distributor Valve Kit) and the noise is now gone.