F451

Hey guys,

I need some help diagnosing a loud buzzing from the fuel tank area on my '88 S4. I'm here in NJ picking up my new S4 and am prepping it for the drive back home to Seattle (follow that saga here: https://rennlist.com/forums/928-forum/323609-nj-to-seattle-road-trip-starts-tomorrow.html

I'm assuming its the fuel pump, but would welcome any input. I checked the manuals, and it looks like there is a fuel pump mounted external to the fuel tank, and it looks fairly easy to access and change out. The fuel filter looks like it is right there too, so I will likely change that out too.

Does anyone know if that is correct on the S4, that the pump is external to the tank?

Otherwise, the car runs fine, but the buzzing is very noticable and fairly loud. I'm assuming the fuel pump is not something I can source at a local parts store (although I guess I could call one of them and double check), so I've sent an email to rixter down by dc to see if he has a fuel pump.

If rixter has a fuel pump I will head down there to and install it myself. I'm keeping my fingers crossed and hoping the pump will last for the 4 hr or so ride down there Monday (assuming he has a replacement pump for me).

Anyway, any tips or info would be greatly appreciated!

Thanks,

Ed

killingmoon65

Mine buzzes pretty loud as well and I just installed it a few months ago. May not be a failing pump. Might just have been mounted improperly where it is not insulated. Starts and runs OK, even in the higher rpm range?
I don't know if your pump is in-tank or not. Mine is a 78 and external.

F451

Yep. Starts right up. Idles nicely, nice and smooth. Revs freely, no stumbling. Drives fine, revs up nicely under load.

I did not get a chance to take it out on the highway for any extended runs, but I will be on the highway with it today for a couple of 1 hr runs, so will see how it does then, but I suspect it will be fine as my brother had picked the car up for me and drove it home to his place on the highway, and other then the loud buzzing, he said it did fine on the highway.

I am planning on getting under there this morning to see if I can see if the fuel pump is mounted externally. If so, I'll double check how it is mounted to make sure it is secured properly.

Thanks. -Ed

WallyP

Before buying a pump, pull the cover forward of and above the rear bumper cover, and check the lines and pump carefully. If the pump is turned the wrong way, or if an insulator mount is bad, a line can touch the sheet metal. This will cause the normal pump buzz to be loudly telegraphed to the world.

A plugged fuel filter will also slightly increase the noise level...

chaadster

Ed,

Check Tony H.'s site for good pics/writeup of fuel pump R&R: http://members.rennlist.com/v1uhoh/

F451

I will be under there this morning, so will look into that. Thanks!

F451

Sweet! Got it printed out. Thanks!

C.F.

Don't all USA cars have an in-tank pump as well ?
A friend of a friend's GTS had the loud buzzing from the back, main pump was ok, it was the in-tank pump which you can isolate by disconnecting the power wire to it.Car still ran ok with just the main pump running, I don't know if he connected the in-tank pump back up though or left it disconnected.

daveo90s4

My S4 has almost new intank pump and new main pump and makes a discenible buzzing noise sometimes, especially after a brisk drive. So I don't think the buzzing noise is necessarily a sign of imminent failure. I was told some time ago that fuel additives to clean injectors can make this noise occur - though can't see how / why.

(The rubber connector on the intank pump is prone to failure, resulting in a pump that simply pumps fuel around and around the fuel tank rather than up the line to the main pump)

ew928

Fuel injector cleaner has been known to dislodge gunk in the fuel tank that gets sucked into the pump causing problems. Allegedly.

I've added Techron to my fuel system with no ill effects.
US model 88 with no intank pump.

Ernest (NYC)

mark kibort

ive chased this for a long time. a new pump fixes this. its the motor inside that is vibrating and could be failing. never had a failed unit and have raced on one for a few weekends. now, its in my bag as a spare and a new one is in the car! It's the pump, but dont know how terminal the problem is.

Mk

chaadster

Not all USA cars have an in-tank pump, e.g. my '88 does not.

FWIW, I drove for months with a buzzing pump, so like DaveO, I don't think the buzzing is an immediate precursor to failure. It is annoying, though! And, with a cross-country trip on tap, why bother with the risk?

F451

Great, thanks for the info guys! I'll see about sourcing a replacement pump and installing it. -Ed

Charley B

Be sure you have isolated the sound to the fuel pump. The TC bearings and TT bearings can make some strange whirring and buzzing sounds also.

BrianG

Also, try listening for a difference in tone of the sound with a full tank of fuel. Mine buzzes at less than 1/2 tank but has essentially no noise above 1/2.