I ask this because when using a fuel pump to empty my fuel tank (electrical and a rubber hose connected and then stuffed into the filler neck of the tank) I found that if I hooked up the pump with reversed polarity - the pump flowed the fluid backwards. This would say to me that the fuel pump does not actually have a check valve, but has positive displacement and tolerances tight enough that it does not allow the fluid to flow without the rotation of the pump.

Anyone else find the same thing? A pump hooked up with reversed polarity pumps fluid backwards?

If this is true - pumps don't have check valves - then a pump that leaks pressure would indicate a worn pump.

http://reddevilriver.com

[This message has been edited by phonedawgz (edited 09-30-2011).]

Interesting.

My E85 pump has an external check valve. Without it it does not hold pressure.

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Turbo 3800 E85 5spd spec5
11.53@126.7

I heard they do.

YES

Pressure Leak test from, I think, SM.

Should retain pressure for some time w/o engine and pump on. Short time, but not instant to kill system. I can't find detail...

Yes EFI fuel pump, like oil pump and Roots Blower, is positive displacement pump. One of reason why FP needs constant flow... Blocking fuel can overheat very fast by cutting cooling flow while spiking Amps. 1 2 punch will damage/destroy pump.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

I suppose some do and some don't.

http://www.aa1car.com/libra...el_pump_diagnose.htm

See ----Residual Fuel Pressure Test

So has anyone else connected a fuel pump with it's polarity reversed and found that it pumped fuel backwards? or has anyone found that with the polarity reversed it didn't pump at all?

Last time I hooked one up backward was on a plymouth mini van and it didn't pump at all.
I find it interesting if your would pump backward drawing in the output port...