an ingenious person can do anything.The auto makers sell more parts and
service
by making things (harder)more cost efficient
old john

Hello, Nehmo!
You wrote  on 22 Apr 2006 22:04:37 -0700:

N> But I was wondering: Since the in-the-tank placement makes this pump a
N> chore to replace, isn't another design possible? What about sending
N> pressurized air into the tank, and at the bottom of the tank have a
N> pick-up tube for the fuel. The fuel (forced out the tube by the air)
N> could then be additionally pressurized by outside-the-tank pumps.
N> Wouldn't this two-stage process work?

N> Also, in the existing in-tank placement, since running out of gas hurts
N> the pumps by depriving the pump of coolant (the fuel), why not have a
N> cut-off switch that works by the float? There is a float on a leaver in
N> the pump assembly, but it doesn't look like it does anything electrical
N> for the pump. I think it's the fuel level sensor for the instrument
N> panel gauge. A fail-safe circuit could be designed to work with this
N> sensor. When the level gets too low, the pump could turn off.

With best regards, ajeeperman@comcast.net.  E-mail: ajeeperman@comcast.net

 OK. First, you're not supposed to constantly run the vehicle low on fuel. Do you
just fill to 1/4 tank at a time? If not, overheating of the pump is not an issue.
 As far as your two stage design, it would add unnecessary complexity and parts to
the fuel system.
 As for the complexity of replacing the pump in your Ranger. Did it ever cross your
mind to remove the 6-8 bolts in the bed (along with 4 screws for the filler neck and
one electrical connector for the rear lamps), then slide the bed back, and do the pump
right there in front of you (with lots of room to lay tools, fasteners, your beverage,
and even your lunch if it's that time of day)?
 Think the project through sir!! It's 3 hours IF you break for lunch.

1. Two fail items instead of one
- Ford's mid 80's system used the two-pump method

2. Pressurized air into the tank.  
- Interesting concept... Can we say "Stoichometric?"  Heh Cant even type
it...  suffice to say, get your such-equipped vehicle under cover in event
of lightning storms... and pray your Fuel level sending line doesnt short
out.

Faithful readers of your posts????  A bit presumptuous on your part to
think you have an audience of the faithful.

Why not just replace the original pump with another factory unit.  Did
the pump really die on a 5 year old car?

Sounds like a good idea.  Just run a hose to the drivers seat and blow
on it periodically.

If you are worried about that issue why not try the simple 100%
effective solution - keep the gas tank over 1/4 full.

Sounds like a project for someone with a lot of time on his hands.

Yes.  It also solves the tank venting issues.  The problem is that the
failure modes in case of a tank leak or an accident are a lot worse than
with an unpressurized tank.

My argument against this is that it's another attempt to use more
electrical and mechanical stuff, which is prone to failure just because
of the nature of electrical and mechanical things, to solve a problem
caused by careless operators.  I think that's usually a bad thing.
--scott

In our last episode, we saw our hero, Nehmo, laying in the sodden Kansas
mud, various bits and pieces of his fuel system gathered about him..... The
saga continues...

As the sky darkened and the gentle breeze gained passion, our hero's dog,
Toto, moved closer...... after whizzing on the left rear tire.... suddenly,
Nehmos world turned topsy turvy.....

As he regained equilibrium, our hero said "Oh, Wow, Toto.... we ain't in
Kansas anymore..... I got the munchies....". And the two combined talents to
design a fuel system that Rube Golberg would be jealous of..... after nehmo
whizzed on the left rear tire....

sh.t happens... some sh.t happens before we expect and other sh.t never
happens..... In our modern world (spelled "mass production"), two seemingly
identical items can be like night and day in regards to traits such as
overall quality, general metallurgy, fit and finish and internal
clearances.... These factors can have an effect on the life span of any
component.

FWIW, my experience tells me that THE MAJOR cause of fuel pump failure is
neglecting to change the fuel filter in a timely manner. If this truck has
ever been run to the point where a restricted filter has given driveability
issues, we can expect a premature fuel pump failure (even though we don't
know how many miles or hours are on this nearly 6 year old pump).

If we have ever experienced the inconvenience of a flat tire, we don't set
about designing cast iron tires.... If we have ever had a rock chip in a
windshield, we don't come up with wire mesh guards....

As for introducing air into the fuel tank.... the motor on the electric pump
uses a commutator and brush arrangement. As each commutator bar breaks
contact with a brush, a spark occurs..... Your truck doesn't blow up because
the fuel vapours in the tank are well above the UEL (upper explosive limit).
If we introduce oxygen into this vapour rich environment, we can bring this
mixture into the explosive range. And we are still left with the possibility
of starving our newly positioned pump.

There is no real concern with allowing our fuel level to drop below 1/4
tank.... but should we allow the level to remain there? As temperature
changes, so does the dew point.... condensation can settle on the inner
walls of the fuel tank find it's way into the bottom of our fuel tank.
Additionally, keeping the tank close to full means we have one less concern
should we have the need to suddenly travel any distance... one less concern
should we find ourselves in a position where we can't find a fuel source...

While I would imagine that most reading this have experienced a fuel pump
failure in their lifetime, I doubt that you'll find many that have
experienced multiple fuel pump failures. My last bad pump was on a car with
a carburettor...

My race car works this way, but it runs on methanol. I'd be hesitant to
use it with gasoline because of the explosion hazard with gasoline. In a
crash the fuel may spray all OVER the place.

How about using one of the older electric fuel pumps like an autopulse.
 That SUCKS fuel through the fuel line.  You might have to take an old
tank pump and remove valves and stuff, but the autopulse may suck
through the in-tank pump and be mounted on firewall.

You are way, that's WAY, over engineering this thing. Or way over thinking
it at the very least.

I have an '81 Jeep CJ5 that I converted from a crappy carburetor system to
multi port fuel injection. the fuel pump for the MPFI is external to the
tank, and connects to the pick up that the old mechanical pump was hooked up
to. The electric fuel pump sucks gas from the tank, pulls it through a
filter, then pumps it to the injector rail. No need for pressurized air to
get the pump going. Replacement is easy, well that's relative I suppose. All
I need to do is raise the vehicle by the frame so the rear axle drops, and I
can get to the fuel pump without much trouble.

I see no reason why the Ranger could not be fitted with an external fuel
pump. Having said that, the internal pump has several operational
advantages, and if you keep gas in the tank, it should last a very long
time. The gas acts as a coolant, drawing heat away from the pump and
dissipating it. The need to replace an in-tank fuel pump is often associated
with running the gas to the bottom before refills. Yes, there can be other
causes, but you can control the fuel level easier than you can control the
other causes.

Look here...
http://www.mkiv.com/techarticles/fuel_pumps_test_2/fuelpumpdiagram.gif

As shown the fuel flows THROUGH the motor.  Thus pump will only overheat if
there's no fuel flowing.  and if other electronics are right, it wont run
long if there's no fuel to flow.

While the low-tank syndrome applies regarding sporadic flow, once the
engine doesnt get enough pressure, it will stop, and then the Fuel Pump
will stop, as well

Solution, dont worry too much about maintaining 1/4 tank...DO gas up when
the needle hits 'E' or low-fuel lite comes on

Work?  Yes.  Needed? No.  Further, you would have to take care to filter
the "blown" air.  A pressurized tank would need to be carefully designed
to be opened for filling without "burping" gasoline (pressure release
before openning).  A pressurized tank might be considered a higher
explosion hazzard.

The existing design is meant to reduce cost of manufacture.  These pumps
usually don't die for the lifetime of the vehicle.  You're unlucky,
that's all.

They could use a more simple detection method in the fuel line or the
pump itself.  I agree on this as my SO killed her fuel pump recently
after the second time she ran out of gas (because the gas guage
indicated nearly 1/2 full when in fact it was empty).  Crappy Chevrolet.

Cheers,
Alan