Forwarded message:
> From alliant!UUCP Wed Jun 20 08:19:52 1990
> Errors-To: british-cars-request@alliant.com
> Sender: british-cars-request@alliant.com
> Date: Wed, 20 Jun 90 06:37:46 EDT
> From: mason@vax.ftp.com (Nark Mason)
> Message-Id: <9006201037.AA25367@vax.ftp.com>
> To: british-cars@alliant.com, phile@pwcs.stpaul.gov
> Subject: Re: Facet fuel pump
>
> If it only has 1 wire coming out of it then you have to pay attention to
> if it's a pisitive ground or negative ground. If it has 2 wires, measure
> the resistance from the body of the pump to each wire. If there's no
> resistance the your cars ground doesn't matter. I wonder if it'll pump
> the gas from the carbs to the tank if it's wired backwards...
>
I don't know 'nuthin 'bout them thar fancy Facet feul pumps, but the old
fashioned kind wouldn't care about reversed polarity. Basically what I've
seen are fuel pumps that look something like this (aren't ascii drawings
fun?):
Electricity Calibrated
of some random spring Fuel in
polarity | | |
| Plunger V |\/| <- One way valve
| | ________| |_____
========= V ##| / / / / /
Electo- H H----------/-/-/-/------ Pressurized fuel comes
magnet H H---------/-/-/-/------- out here
========= H ##|/ / / / ___\_____________
| I
| HB PHI# ^ ^
|________| ^ HI# | |
/ | | Cylinder
/ | Rubber
Points that | seal
close when Electricity
plunger is of the other
fully released random polarity
The idea here is that the plunger is pulled back by the electromagnet
whenever the points close. The points only close when all of the fuel in
the cylinder has been forced out by the spring. The actuation of the
electromagnet brings fuel into the cylinder so the spring can force it out,
causing the points to close, engaging the electromagnet again, etc. This is
the clicking that you hear from the ubiquitous SU fuel pumps. The spring
determines the fuel pressure.
I once worked on an MG-TC (I'm not sure if the rest of the T series has this)
that had a fuel pump made out of clear plastic of some sort, mounted
prominently on the fire wall. You could clearly watch the operation of this
pump. And with good reason, too. On this particular car, one of the things
that kept it from running was that the fuel pump points needed to be cleaned.
Joe
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