In-the-tank fuel pumps cause death and destruction

I believe the original poster said transfer pump, not the car's fuel
pump. That method would work just fine.


Matt

 

Are you sure? Let's do a little math. A quick Google on "electric fuel
pump" gph shows us automotive pumps with volume flowrates of from 43 to
220 gph on the first page alone. Take the lowest-rated one (43 gph). Half
of 43 gallons per 60 minutes is 21.5 gallons per 30 minutes.

 

I'd have no qualms being that engineer, and here's why: Gasoline is
combustible in only a narrow ratio range with air. Bored suburban kids
used to get empty paint cans from the hardware store, put a barbecue
sparker with long leads in the side of the can, use an eyedropper to put
two drops of gasoline in the can, hammer on the lid, stretch the sparker
leads and hit the button to cause a loud noise and a flying can lid.

One drop of gasoline didn't work. Three or more didn't work. TWO drops --
and only two drops -- worked.

The ratio of fuel to air is always much too high (or, if you prefer,
the ratio of air to fuel is always much too low) for these hallucinatory
panoramas of firy death some people (even engineers, amazingly enough)
have been talking about in this thread. That's why they don't happen.

DS

 

Well, I suppose this means that you haven't heard about enough
of them then. Even with dropping fuel tanks, most of them are not
nearly as hard as you might think. You are comparing replacing
an electric fuel pump that is "outside" the fuel tank to replacing
one that is inside the fuel tank. I was thinking more along the lines
of the older mechanical fuel pumps that were attached to the engine.
These were far more common on domestic vehicles then inline
external electric fuel pumps.

Many late model vehicles also have access panels in the trunk that
make changing an electric fuel pump a 15 minute job. Most vehicles
that I work on (GM), you can have the fuel tank out in 10 minutes.

Ian

 

Yes he was referring to a transfer pump. Even with a transfer pump, he will not
remove 19 gallons or 72 liters in a half an hour. The lines are too small in
diameter. There is restriction from both the pump in the tank and fuel filter.
Then once the return line is no longer under fluid the possibility of sucking
air if the regulator is of an open center design. Which means you can no longer
pump fluid.

 

A lot. What else is there (in modern business thinking)?

Having worked in the industry for 7 years, I believe that the primary
driver for designs is intial cost to the mfgr., whether in the form of
parts cost or assembly labor. *IF* it can be determined that making
repairs easier and cheaper will help the mfgr.'s bottom line (i.e., if
the buying public becomes painfully aware of the extra cost of ownership
due to a poor design), then that may influence the design. In
MBA-think, if it hurts the customer or costs the customer money, but the
customer never recognizes that to the point of affecting buying
decisions, then there is no value added in making the design better. No
matter how it's sugar coated, in reality, the term "value-added" means
"it improves our profits". IOW, if it is an improvement (for the
consumer), but doesn't ultimately help the bottom line, then it isn't
"value added" (in MBA-think).

Possibly if it is considered to be a high rate of warranty repair item,
then that might be factored in too. But I believe in this case, the
prime motivator was total initial cost to the mfgr. IMO...

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

The average automotive OEM not a aftermarket high flow pump is 19 to 30 GPH (
Gallons per hour ) not the advertised GPH of the high performance pumps on the
first page of your google search. Pumps as a rule do not deliver the maximum
advertised GPH when plumed in. There are a lot of reasons for this. One of the
biggest is the size and lengths of the lines the pump must push the fluid
through. The same holds true for the supply side of the pump. The amount of
restriction in the filter must also be considered. You will never see the pumps
rated flow, especially through the very small opening of the Schrader valve. But
for argument sake the highest average for OEM is 30 GPH, is a max of 15 gallons
in 30 minutes, if there is no restriction involved, but we know there is.

I routinely fill 2 and 5 gallon fuel cans for my home power equipment via the
fuel pressure Schrader valve. It takes roughly 7 minutes to fill the 2 gallon
can. So 3.5 minutes ( for one gallon ) x 19 gallons is 66.5 minutes. The pump is
new, well less than a year old. I can shave a about a half a minute if I remove
the Schrader valve core. 3 x 19 = 57 minutes.

 

I thought I could find a flow table with a quick search, but no luck
yet. I think you'll find that even a 1/4" tube will flow a lot more
gasoline that you might guess. 19 gallons in 30 minutes is only 0.63
GPM, and that is really a very low flow rate given any pressure at all.

Matt

 

Maybe if it's the sending unit that is not working?? Or maybe the tank
itself that needs replaced??

I'm not always in a hurry to do a job. If it works out, sometimes I'll start
draining the tank on one vehicle while I'm finishing up another job. It does
cut into my bullshit time but I make more money. <G>

Denny

 

Are you suggesting buying a 3rd pump so that you can drain the tank
to eventually install the 2nd pump???

 

Hey hey hey! One question at a time! 8^)

Actually, the commutation (brushes) are in the fuel that is flowing thru
the pump. The motor armature, magnets, pumping elements, and commutator
are in the same compartment swimmimg/spinning in the fuel.

Nope. The "bearings" in the ones I worked with (supplied to GM and
Ford) were simply holes molded into the plastic end caps of the motors -
again - in fuel. That is typical of the modern automotive fuel pump.
One reason fuel pumps can become noisy is that those plastic bushings
wear (actually, usually the metal shafts wear a lot faster than the
plastic due to abrassive glass fibers in the plastic) and the armature
starts rattling around.

No - but there are brushes.

Magnetic drives are a great way of eliminating rotating seals, but that
magnetic drive wouldn't transmit the torque needed to develop 60-90 psi.
8^)

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

Well, Thomas, we're arguing from what we've done and what's worked. You,
on the other hand, are insisting that it couldn't possibly work.
Difference is, we've done it and it has worked.

 

That was cold! 8^)

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

Well lets do the math. As I stated in a another post it takes about 7 minutes to
fill a 2 gallon can from the schrader valve on my car. That is 3.5 minutes per 1
gallon with a stock OEM pump. 3.5 minutes x 19 gallons is 66.5 minutes. The
pump in my Crown Vic is rated at 21 GPH. It delivers out the schrader valve at
just under 19 GPH. That is why I say bull-shit to the claim of pumping out 19
gallons or 72 liters in half an hour. It can not be done with a stock pump in
the tank, and it cant be done with a transfer pump pulling the fuel out the
schrader valve. That is especially true if the pump in the tank does not work,
it will provide too much resistance to the flow and most likely cause the
plastic fuel lines to collapse.

 

The claim was to be able to pump out 19 gallons in 1/2 hour through the fuel
pressure port on the fuel rail. It can not be done. The pump on a Crown vic is
rated at 20GPH. To make the claim true you would need to at least double the GPH
and take away the normal restrictions of the fuel system. I did not say you can
not pump fuel from the pressure port, I do it on a regularly. I'll say it again,
it takes on average 7 minutes to fill a 2 gallon fuel container. Do the math.
The claim is bull-shit.

 

Were you by chance a bored suburban kid, or were you the kid behind the
counter at the hardware store (or both)?

Ouch!!

Forget for the moment that you are technically right. You think you
could convince the management, lawyers, insurance companies, and stock
holders that, statistically over the lifetime of 20 million vehicles,
the perfect conditions resulting in huge publicity and multi-million
dollar lawsuits would never be met - not even one time? You know -
seriously - taking your paint cans and eyedroppers into the conference
room just might do it.

Reminds of the engineer that told me I was over-reacting when I went
ballistic when a 3 foot long flame shot out of a known leaking hydrogen
fitting due to a welder welding above it and showering down sparks - oh
- he had draped the hydorgen equipment with a canvas tarp before he
started "to be safe". He was telling me that the conditions for
hydrogen exploding were so specific that the chances of it happening
were extremely small. The funny thing is that hydrogen in a process
oven not 10 feet from that very spot where the flame shot out had
exploded, blowing the door off of the oven so hard that it moved a 40
ton press a few inches when it struck it. Fortunately, no one was
standing in front of the door at the time. Here's the kicker: That
incident happened - not *AFTER* the 3 foot flame incident, but 3 years
*BEFORE* that - and he still told me I was over-reacting - that an
explosion could never happen.

Saying "Oh - that could never happen - let's go ahead and do it" is how
you end up on the 6 o'clock news. 8^)

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

That's odd, my Service Manual still refers to it as the 'firewall'.

 

Hi...

If it isn't to be referred to as a firewall anymore; then
I doubt it's to prevent my believing that a fire is
possible...

Be more inclined to think they don't want me assume
that their firewall would necessarily protect me
from one.

Take care.

Ken

 

Correction - it was a 15? gallon tank in less than 1/2 hour. 1983?
Toyota Supra.
That is roughly 68 liters? Been a few years so I'm not 100% sure of
the tank size.

The transfer unit used a roller cell type external EFI pump rated for
something like 350HP or 150 liters per hour at 20 some PSI IIRC.
Emptying the tank through the line was about 30% faster than through
the access valve. Flipping a pair of valves on the unit and dropping
the hose into the filler neck refueled the car in something like 20
minutes.
Trying to suck the fuel out the access port with the valve installed
was hopeless..

 

I'm talking about doing it in the shop, where safety regulations
REQUIRE a fuel transfer pump/tank unit. I made the unit we used for
about 6 years while I was service manager - and it may still be in use
today. I left the dealership in question about 18 years ago