Buzzing noise from fuel tank

[Mike Arman <armanmik@n-jcenter.com>]

>From: "mlcmlcmlc" <mlcmlc@enter.net>
>Subject: Re: Buzzing noise from fuel tank
>
>Guys,
>I hate to say this, but if it's a 5000 TQ your speaking about, I must
>disagree.  My car was making what was only described as "fuel pump" noises
>when I bought it with 89,000 miles on it.  I drove it like this for three
>years and finally because I figured I was on "borrowed time, I put in a new
>pump @ 146,960 miles. (This is all written down in the back of my Bentley).
>
>Guess what ?? The new pump didn't sound any different, it still growns /
>mowns away back there...its a noisey little sucker. At 207,000 and change it
>sounds identical to when I bought it (with the old pump).  Is this a
>standard "problem" that others have found ?
>
>Joel Stetina  91 200Q Avant, 87 5000TQ, 79 323i, & two wheeled missles.


There seems to be a difference of opinion about exactly *WHAT* the fuel
pump noise indicates.

Here's my experience - 86 5000CS - fuel pump just audible - on advice of
very good independent Audi mechanic with plenty of mid-80s type 44
experience, replaced it with one he GAVE me (!) - the source for the one he
gave me was a warranty take-out from when he worked at local dealership. He
stated that Audi's policy was "If you can hear it, change it." Replacement
pump much quieter than the original, but if you listened carefully, you
could hear it. (Which I didn't mind - I figure if I can hear it working,
its OK. - and I like "mechanical" type noises anyway - reassures me that
everything is running properly . . .)

Took apart old pump to see a) what's inside, and b) what's making noise.
Answer to a) is not very much - motor, eames type rotary pump, filter
screen, not much else. Incidentally, the pump and DC commutator (sparks!)
are IMMERSED in gasoline when operated - who me, nervous? Motor and pump
cannot be taken apart without destroying housing, so there's no fix.
Replacement only. Answer to b) don't know yet - couldn't find anything.

"New" pump got gradually louder over the next year or so, but oddly enough
seemed to be temperature dependent - sometimes silent on startup, noisier
once warm, sometimes reverse. Changing the big underhood filter DID make a
difference - pump was much quieter for about a week, then returned to same
level. Finally became loud enough for wife to notice, and she notices
NOTHING automotive. ("Honey, what's that red light? It's been that way for
three weeks now.")

Also noticed that when the tank was full, the noise was less (probably
damping from liquid gasoline?). 

One fine afternoon I started the car in my driveway at the office - started
right up, ran about three seconds - then died. Stone dead. Phfft. Party
over. No noise whatsoever from fuel pump, cranked but wouldn't start. (Got
ride to aerobics and home.)

Next AM, changed fuel pump AGAIN using ANOTHER used pump (don't remember
source) - car started right up, new(est) pump was and still is TOTALLY
SILENT - so far so good (6-8 months).

Took apart failed pump - found pump rotors seized - wouldn't turn.

I'm thinking that the noise is from the motor part of the pump and can stem
from several reasons - if the pump is laboring, either from a clogged
filter under the hood OR a clogged screen in the pump (gas tank coating
flaking off) OR a seizing pump mechanism, then the MOTOR will complain and
make the noise we know (and love).

On my 5KQT, the pump is also totally silent, but since this is a new car to
me, I am not yet familiar with the "normal" noises from it.

My conclusions: Silent pump is OK (unless it is dead), and can be
considered the "normal" state. Minor noise is acceptable, as long as it
doesn't change or get louder or vary with fuel tank level, etc. It *IS*,
however, a heads-up that trouble is eventually coming OR that something
else in the fuel system might need attention (big filter?). Loud pumps and
pumps whose noise level change unpredictably are doomed - soon.


Best Regards,

Mike Arman