Subaru Fuel Pump Ground Wire?

M

Michael Streck

I have gone through 5 fuel pumps in two years on my 1992 Legacy. No
one (even the dealer) has a clue as to the problem. It has been
suggested that I run a new ground from the fuel pump to the frame. Can
someone tell me how to locate the original fuel pump ground wire?

Thanks,

Mike
 
Mike:
The fuel pump wiring is visible under the rear seat, but there are also a
few wires for the fuel level sender in the tank. The later AWD cars have 2
fuel senders, not sure if this is the case on yours (is your car FWD or
AWD?). The pump is under the cover that has hoses coming out of it. Chck for
voltage with a multi meter (with the ignition in the on position), and you
can tell which wire is positive and negative with the meter. To ensure you
are checking the pump wiring, pull the pump fuse and test again, if no
voltage, you have the right wires. Connect some wire to the ground
wire(solder it to ensure a good connection), and ground it with a self
tapping screw anywhere convenient on the metal under the seat.
 
I have gone through 5 fuel pumps in two years on my 1992 Legacy. No
one (even the dealer) has a clue as to the problem. It has been

Is the fuel pump in the tank? Do you often run until the gauge is on
empty? If both are 'yes', that could be the problem.

I've read elsewhere that in-tank pumps depend on being covered by fuel
to keep them cool, and thus to prevent them from burning out, you need
to be sure to never go under 1/4 tank.

Steve
 
Steve said:
I've read elsewhere that in-tank pumps depend on being covered by fuel
to keep them cool, and thus to prevent them from burning out, you need
to be sure to never go under 1/4 tank.

You gotta love a design that takes an overheating electrical
device and submerges it in an explosive liquid and at the same
time allows a rupture in the fuel line to spray gasoline
all over a nice hot engine.

I mean, you GOTTA love that.

-DanD
 
Dan said:
You gotta love a design that takes an overheating electrical
device and submerges it in an explosive liquid and at the same
time allows a rupture in the fuel line to spray gasoline
all over a nice hot engine.

I mean, you GOTTA love that.

LOL! Have you thought about the fact that the brush commutation (i.e.,
lots of sparks) also takes place in the fuel (I know - the third
component - air/oxygen - is missing - but I always try to keep myself
more than one failure mechanism away from death whenever I can). 8^)

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
 
I've read elsewhere that in-tank pumps depend on being covered by fuel
to keep them cool, and thus to prevent them from burning out, you need
to be sure to never go under 1/4 tank.

Do you have a reference for this "fact"? Considering the number of
people who run ther cars with less than 1/4 tank of fuel, I have a
hard time believing this is true.
 
Victor said:
Do you have a reference for this "fact"? Considering the number of
people who run ther cars with less than 1/4 tank of fuel, I have a
hard time believing this is true.

Though there are some here who I respect but who would (no doubt
politely) disagree with me, I also question this accepted "fact".

As a veteran fuel pump components designer, my 2 cents is this: Cool
fuel flows thru the pump (all around the armature and inside the
case/magnet housing). Though the fuel surrounding the "can" certainly
would contribute something to the overall cooling, my guess is that it
has, at most, a second-order effect to local peak pump temperatures
relative to the internal flow (primarily because the external flow is
not in direct contact with the primary heat-generating components, such
as armature and brush/commutator interface). Because of this, I believe
that the most that can be said about running with the tank low in fuel
is that it reduces the design safety factor a little. I'm only a sample
of one, but I sold my '86 turbo wagon last year with 275k miles on it
and the original fuel pump, and I never paid much attention to keeping
the fuel level up.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
 
I remember having a fuel pump discussion where it was brought up that
most (if not all) FI pumps were of the roller cell variety - a type of
positive displacement pump. This, combined with the fact that the
motor was a DC series wound type (will over-rev with no load) would
mean that these pumps should never be allowed to suck air. In
addition to over-revving, the rollers can overheat very quickly if
they aren't immersed in fuel.
1/4 tank might be overdoing the safety thing a bit, though. I usually
start looking for gas as soon as the warning light comes on. That
gives me over a gallon sloshing about - keeping the pump happy. I
also put 4 oz. of Marvel Mystery oil in every tank th help keep the
pump and other parts lubricated.
 
Bill Putney said:
LOL! Have you thought about the fact that the brush commutation (i.e.,
lots of sparks) also takes place in the fuel (I know - the third
component - air/oxygen - is missing - but I always try to keep myself
more than one failure mechanism away from death whenever I can). 8^)

Air is only missing from the fuel tank when full. When the level
drops, the missing gasoline is replaced with air... air that's
chock full of vapors. When you get real low on fuel and it sloshes
around when you speed up, slow down, or turn, you can even suck
air into the pump.

I prefer not to think about it.

Hey, ever been in a car that had the fuel line spring a leak? With
a tank-mounted fuel pump it just keeps right on pumping and spraying
that gas all over your nice hot engine. It happened to a friend of
mine driving down the autobahn.

The car was totalled.

Another friend had a leak in his fuel line but since the pump wasn't
mounted in his tank it resulted in air in the fuel line.

The car stalled.

I don't about you, but I don't care for in-tank fuel pumps. It makes
working on them much more dangerous if you have to remove the fuel tank.

-DanD
 
Dan said:
Air is only missing from the fuel tank when full. When the level
drops, the missing gasoline is replaced with air... air that's
chock full of vapors. When you get real low on fuel and it sloshes
around when you speed up, slow down, or turn, you can even suck
air into the pump.

I prefer not to think about it...

I hear you on that one. When I used to work on design teams as a
supplier on GM/Delphi and Ford fuel pumps, I used to say to their
engineers that if I had been the first engineer to think of running fuel
through the commutation area of an electric pump, I would have kept my
mouth shut. I also am convinced that, if that were not already being
done today, in today's legal climate, *no* manufacturer would ever be
the first to try it after the company lawyers looked at the idea.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
 
Bill said:
I hear you on that one. When I used to work on design teams as a
supplier on GM/Delphi and Ford fuel pumps, I used to say to their
engineers that if I had been the first engineer to think of running
fuel through the commutation area of an electric pump, I would have
kept my mouth shut. I also am convinced that, if that were not
already being
done today, in today's legal climate, *no* manufacturer would ever be
the first to try it after the company lawyers looked at the idea.

Don't let lawyers make design decisions, there are more quantitative ways to
make such decisions. Given that cars with nearly empty gas tanks are not
blowing up everyday (sample of millions) I gather this design has proved to
be quite effective.
 
You didn't indicate whether yours was a turbo or not, but on turbo models,
the fuel pump connector can become burnt, causing a no start condition.
Just to eliminate the potential, pull up the rear seat and have a look at
the connector. Pull it apart and examine the connectors. If you see any
black or brown marks, you may have located a potential problem.
 

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