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Old 08-20-2008, 03:17 PM
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electric fuel pump question :

I know this is not on a 'hotrod' (motorhome) but,how does the electric fuel pump work ? Isn't the pump supposed to stop when a certain pressure is reached ? This one pumps about three pounds, slows down very little, but, keeps on clicking. Shouldn't it stop untill the pressure comes down ?

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Old 08-20-2008, 06:07 PM
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Is this a factory pump or an aftermarket? I remember some of the old type electric pumps that were mounted outside the tank do just what you describe.


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Originally Posted by knighthawk
I know this is not on a 'hotrod' (motorhome) but,how does the electric fuel pump work ? Isn't the pump supposed to stop when a certain pressure is reached ? This one pumps about three pounds, slows down very little, but, keeps on clicking. Shouldn't it stop untill the pressure comes down ?
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Old 08-20-2008, 08:44 PM
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yes, it is an original pump, 20 years old, 100,000 miles. mounted on the frame near the fuel tank. IF, this is normal ...then... the new replacement pump I bought ,dosen't say it has a built in pressure switch either , so it also will pump all the time ??
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Old 08-21-2008, 05:24 AM
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Most of the newer pumps require a return line to the tank. They pump continuously to maintain pressure and just let the extra fuel return to the tank. This keeps pressure constant. Cycling the pump on and off might work with a carburetor, but the pressure variations won't work with fuel injection.

Bruce
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Old 08-21-2008, 09:11 AM
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so then it would return thru the 1/4'' line at the filter at the engine ? which it should aready have , for the engine mounted fuel pump? Would this one filter have enough return space ?..........update : the in-line filter is the normal (2x4'' round silver one with 1/2'' fittings ) filter commonly used else where, with NO return line. However, there is a return line in the engine (454)mounted fuel pump....I assume this will work ?

Last edited by knighthawk; 08-21-2008 at 10:58 AM.
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Old 08-21-2008, 07:20 PM
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Does the electric pump supplement a mechanical pump mounted on the engine? If there is a return line on the mechanical pump, I guess it could also serve as a return line for the electric pump.

However, i've never seen that setup, so I don't really know. In most cases you remove the mechanical pump when you switch to an electric pump.

Bruce
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Old 08-21-2008, 09:05 PM
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I don't know if it is factory original,but it's been there for the 15 years I've had it, (it's a '89)...I had to change the engine fuel pump once, on the road somewhere, in a K-Mart parking lot(another whole story), anyway I kept the old one, and looking at it yesterday , it 3 lines in it, assuming one (1/4'')is for the return ..........which brings me to my main question :the instructions for the new electric pump,(which I haven't used yet ) says to install the electric pump in a kinda 'by-pass loop' with a check valve in the main fuel line 9 by pass going around the check valve ), so the mechanical pump can draw fuel thru the check valve when the electric pump isn't running... which tells me that the gas can't be drawn thru the electric if it isn't running ?????..........Also it takes a good suction to open the check valve.........wouldn't leave much suction to pull the fuel from the engine pump ....................now I drove it over to the fishing Lake and campgrounds today(only a couple miles , but hilly ) and the sucker really ran great ! And with the electric pump off...............comments?
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Old 08-22-2008, 07:23 PM
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I only have experience with the older generation of trucks (73-87), and then only with the carbureted versions.

I would try posting a message on a Chevy specific site, like http://www.chevytalk.org/fusionbb/ in the section on your vintage of trucks (you'll have to scroll down quite a bit).

Bruce
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Old 08-22-2008, 08:16 PM
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The only reason I can see to have an electric pump near the tank as well as a mechanical pump would be the length of a motor home. A mechanical pump may have a hard time pulling from a rear mounted tank on one of those things, and 3psi is almost inadequate.
Who made the coach?
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Old 08-23-2008, 07:38 PM
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The electric pump is on there because mechanical engine mounted pumps are primarily designed to pump the fuel and will do so over great distances. it is not designed to suck fuel, on a regular car the span from the tank to the pump is relatively short and with the tank usually mounted higher up than the pump you have the power of gravity working for you. In most older motorhomes the tank is usually mounted lower than the pump which is the reason for the electric pump. when you say it ran great on your last trip. was your tank full?
if so, that weight of the fuel in the tank was probably helping push the fuel up to your mechanical pump, so it may not work as well when you start running low on fuel.
I am pretty sure that pump should run continuously. Whatever fuel the manual pump does not need it will send back to the tank through the return.
And, 3 psi is perfectly fine for a carb. engine, all that the fuel has to do is make it through the fuel filter and into the carb bowl, and 3 psi is more than enough pressure for that.
GL,
Tech
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Old 08-25-2008, 08:42 AM
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thank you , that's good news, and no the tank wasn't completly full ( 80 gallons !! ) The original problem., I think was, that the ign or 'run' power...relay somewhere, quit working, had to 'hotwire' it, now is on a seperate switch in the dash, so I think I'll just hook up a (red or green ) indicator litre so I don't forget to turn it off., ,or, IF I can find a run or ACC wire somewhere , and hook it to a relay.....thanks again !!!
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