O/T fuel tank pump

A friend of mine wanted me to check his inside tank electric fuel pump. The pump is out of the tank. It has two wires so I figure one ground one hot. But I got to thinking maybe it isn't full 12 volts since it is inside with all the gas. It is a 92 chevy pickup. What is the voltage for the fuel pump? Thanks stan

Don't know your answer, but wondered how safe that is with an electric fuel pump inside a GAS tank.

Don't make sense to me.

Gary

Pump is 12 volt. It is safe in the tank because the air fuel ratio in the tank with gasoline is too rich to burn.

I was a fuel pump engineer for 22 yrs. and we tested just to be sure. No explosions.

I can't figure that out myself for sure. but evidently it has been proven safe, but I wonder awhile back when side impact did cause explosions?
Since then a lot of manufactures went to the plastic tanks and guards.
I still can't figure out why the wires don't conduct electricity in liquid when the terminals seem to be so open?

OK, so he just went to the trouble of removing his fuel pump, but he's too cheap to replace it without first testing? I've done that job, and I think I'd shell out the 50 bucks for a new pump. This is also a good time to replace the gauge sending unit, which is considerably more expensive.

Gasoline and diesel are nonconductors. Fuel pumps are virtually drowned in the fuel. No oxygen to burn, even if the pump was sparking.

I replaced one in a Chevy Citation. It would cutout just cruising down the highway, but would always restart. I installed a gauge and noticed the pressure dropping during acceleration. I drop the gas tank and pulled the pump and the sock on the inlet pipe was full of rust. I cleaned the tank and installed a new pump. That fixed the problem of stalling. It was a 12 volt pump too and cost around $50.00. Hal
PS: My neighbor said I wouldn't replace the pump. I replied, but you're not doing all this work.

You may be an engineer, but there is nothing dumber than putting a fuel pump in the fuel tank. That's why the car company are in trouble.

(quoted from post at 04:55:04 03/29/11) You may be an engineer, but there is nothing dumber than putting a fuel pump in the fuel tank. That's why the car company are in trouble.

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The aircraft manufacturers have been putting electric fuel pumps in fuel tanks for many years.

"You may be an engineer, but there is nothing dumber than putting a fuel pump in the fuel tank. That's why the car company are in trouble".

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Copied from another site:

In many modern cars the fuel pump is usually electric and located inside the fuel tank. The pump creates positive pressure in the fuel lines, pushing the gasoline to the engine. The higher gasoline pressure raises the boiling point. Placing the pump in the tank puts the component least likely to handle gasoline vapor well (the pump itself) farthest from the engine, submersed in cool liquid. Another benefit to placing the pump inside the tank is that it is less likely to start a fire. Though electrical components (such as a fuel pump) can spark and ignite fuel vapors, liquid fuel will not explode and therefore submerging the pump in the tank is one of the safest places to put it. In most cars, the fuel pump delivers a constant flow of gasoline to the engine; fuel not used is returned to the tank. This further reduces the chance of the fuel boiling, since it is never kept close to the hot engine for too long.
The ignition switch does not carry the power to the fuel pump; instead, it activates a relay which will handle the higher current load. It is common for the fuel pump relay to become oxidized and cease functioning; this is much more common than the actual fuel pump failing. Modern engines utilize solid-state control which allows the fuel pressure to be controlled via pulse-width modulation of the pump voltage. This increases the life of the pump, allows a smaller and lighter device to be used, and reduces electrical load.

Also remember how the fuel guage works. A resistance wire that's above the fuel with a conductor that rubs it. Been doing it that way since the Thirties.

I always heard the reason for putting the pump in the tank is that electric pumps are better at pushing fuel, whereas mechanical pumps are better at pulling fuel.

Carbureted engines only required about 5 lbs. of fuel pressure while injected engines require roughly 40 lbs. Ergo, an electric pump in the tank is far more efficient for producing the pressures injection requires.

Any pump does not perform well while "pulling", mechanical or electric.

Oh sure you're way smarter than ALL the automotive engineers of the las 20 years. That's why you're so rich...

I am kind of like my friend I want ot make sure the pump is in fact bad, and don't just start changing parts. This truck was given to him not running, and had been sitting for a couple years. Stan

On what basis? Its the best place to have it for almost every reason except servicing, and everyone except GM seems to be able to keep their in- tank pumps alive for the life of the vehicle.

Atmosphere in tank is way too rich to burn. Ignition danger is around fuel filler inlet where air mixes with fuel vapours.

The main reason for poly tanks is you can blow mound one with a complex shape to squeeze extra gallons in very cheaply vs stamped steel tanks.

The Chev side impact explosions where created by a news agency by using an aftermarket gas cap that didn't fit right, strapping model rocket motors and igniters.

(quoted from post at 09:46:19 03/29/11) I am kind of like my friend I want ot make sure the pump is in fact bad, and don't just start changing parts. This truck was given to him not running, and had been sitting for a couple years. Stan

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Stan,

Trace the wiring harness to the fuel tank. Should be two wires than have a connector a few inches from the tank where you can unplug the harness to check for DC power. With the ignition key turned to "on", one wire should have around 5v's, the other 12v's but only for about two seconds once the key is turned to the "on" position. Pump hot wire should have 12v's, the fuel gauge should have 5v's. Ground wire should be from top of sending unit on fuel tank to frame. Hope this helps!

And look at what happened to one of there planes over the water a few years ago.

(quoted from post at 16:25:52 03/29/11) And look at what happened to one of there planes over the water a few years ago.

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What I am hearing is "don't confuse this discussion with facts. My mind is made up".

Almost forgot in tank fuel pumps are a terrible idea because everybody loves vapor lock. It way more fun...

While we're at it let's go back to points, I've got nothing better to do with my time than adjust points.

Face it cars today last many times longer than they did even 20 years ago. They are more comfortable to ride in and use much less fuel while producing fewer emissions. I'd be really upset today if even a cheap car couldn't go 100,000 miles without major repairs...