Date: Wed, 13 Feb 2013 23:23:07 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Black Nylon Fuel Return Hose Kink. Opinions? PICS.
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At 10:31 PM 2/13/2013, neil n wrote:
>No, sadly, I was serious about the kinked pipe causing poor flow.
>;^) Thinking more, I "see" what you mean. i.e. if that pipe were,
>say, closed more than 50%, as long as the fuel tank is properly
>vented, it should make no difference to the pump. (he says with a
>slight question mark)
That pump can probably deliver 100 psi if it has to, and it normally
works in the 25-35 psig range as set by the fuel pressure regulator
based on MAP. Within its limits it's a constant-volume device, i.e.
it delivers the same amount of liquid on each revolution of the
shaft. It's simply not going to notice an extra psi in the outlet
line (although that would affect the pressure that the injectors
see? Haven't thought that through thoroughly). And at a flow rate
of a liter per minute of nice watery gasoline I believe it would take
quite a kink to make one psi difference.
>The fuel pump noise is something may have been there all along. The
>air cooled engine was noisier at idle. After I got the Jetta engine
>running "right", I noticed the noise.
In my experience, the pump should be barely audible through the floor
(from the driver's seat) when turning the key on in a quiet
environment. Once the engine is running it should not be audible. A
cavitating pump will be audible over the idling engine, and will be
clearly audible if you crouch down by the sliding door.
>The fuel pump was new at time of swap as was fuel tank, seals etc. I
>deleted the pre pump filter, images:
>
>https://picasaweb.google.com/musomuso/FuelFilterUpgrade
>
>in hopes of quelling the racket (albeit intermittent and not THAT
>loud). The noise, which I assume is due to cavitation, gets worse on
>really hot days.
I think it's stethoscope time. Find out where it's coming from and
whether it's getting transmitted to the body somehow. Start with the
kink, so you can stop thinking about it.
Vapor pressure of gasoline ought to be higher on really hot days,
which supports the cavitation notion. Again, cavitation is a
suction-side problem caused by pressure in the suction line becoming
less than the vapor pressure of the gasoline in the line, likely
directly at the pump rollers.
>Neat tip on the Kerosene. Would not have known that one!
Gasoline would be better, or water; but each has its own
problems. The kerosene might be viscous/lubricious enough to muffle
an otherwise noisy pump. Isopropyl alcohol might work but could
conceivably attack the pump innards.
>The pump is isolated via the OEM rubber bonded mounts.
But it's got tubes and wires attached to it. A mechanic's
stethoscope, or a screwdriver held to the bond behind your ear in a
pinch, will tell you positively where the noise is coming
from. Lisle makes a very nice stethoscope. Pep Boys sell a
completely useless one with a two-part probe shaft (nothing wrong
with that, it's the way they mount the diaphragm and damp the probe
where it enters the diaphragm housing that ruins it). A good
stethoscope, if you drag the probe very gently across a rough
surface, should be painful in your ears. The probe must be free to
vibrate, and the diaphragm gives enormous gain when it converts the
probe vibrations to sound traveling up the ear tubes.
> > If God forbid the bearings are
> > chattering, it will scream in pain and have low output and probably high
> > draw (since the shaft is rolling around the inside of the bearing
> instead of
> > rotating in it). Dreadful horrifying sound.
>
>What kind of current draw would one look for? I saw ~ 2 - 3 Amps on
>the fuel pump/HO2S circuit at idle - 2K RMP.
I don't know. 2-3 amps seems perfectly reasonable consumption for
the pump. The Westy sink pump takes an amp and a half to piddle in the sink.
Yrs,
d
