fool pumps(things that go woooo in the night)

[Bernard Littau]

> I've noticed the same thing I noticed a few years ago, namely, the
> pump seems to make a lot of noise when the car's not under load.
> Cruising along, I can floor it, or drive uphill etc, and the pump
> goes quiet...coasting, foot off the gas, the noise will progressively
> get noisier, slowly, but noticeably...maybe over about 10-20
> seconds(rough guess.)  From within the car, it makes a woooooooo
> noise that occasionally sounds like it's faltering/stumbling(from
> outside, just seems to buzz, without faltering, which is odd) at
> idle.  The wooooooo noise is what varies with engine load.


Hi Brett,

My pump sounds nearly constant in noise/pitch -- as near as I can tell with
the other sounds from the car.  I don't usually notice the fuel pump noise
when I floor it, as I am usually watching the boost gauge and shouting
Woo-who :-)

It is remotely possible you pump is seeing more volts at more rpms, this
would increase the pumps pitch.  How is your electrical system?  Do your
lights dim much when you idle?

It is also possible your pump is barely making the required pressure.  At
idle, it would make max pressure, as you are consuming very little.  As you
use more fuel, you may be loosing pressure, which would cause the pump to
have a lower pitch.  Are you having any stumble problems?  You should hook
up a fuel pressure gauge and check your fuel pressure at idle and while
driving.  If you don't have access to a fuel pressure gauge, at least do the
fuel delivery test.  My old noisy pump did 1.3 liters in 30 seconds, well
over the 700 ml Bentley had as a minimum.

I've been debating hooking up one of these sensors.  Since you seem to have
time on your hands...
[from a post to diy-efi:]
http://www.msiusa.com/pressure_transducers.htm

MSP-400 series takes 5v drive and gives 0.5-4.5v output, very easy
to use. Digikey carries them, ~$100 qty 1. They're stainless steel
isolated and so will handle just about anything that's not super nasty.
Ranges from 15psi to ~10k psi IIRC; the 100psi unit works fine for me.
[end of quote]

Best,

Bernard Littau
Woodinville, WA
'88 5ktq