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Old 05-29-2008, 02:50 PM
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electric fuel pump question

just installed a holley electric blue fuel pump in my car (came stock with a mechanical pump). It came with the regulator since I am running a carb, my question is when i wire the fuel pump up (to a 12v switched ignition power source) won't the pump ALWAYS been running as long as the key is switched to ignition?? The regulator doesn't have a return to tank or any electrical connections just 1 in and 2 out so how the hell does it regulate anything if the pump is constantly running?? By lowering the pressure of the regulator how does this stop the pump from running if the key is turned to ignition?? I am really confused on how all of this works because I know for a fact that by wiring the pump this way it will be running all the time the car is thus creating way too much pressure and flow?? Can somebody please clear this up for me. Maybe it is a variable displacement pump and by chaning the pressure at the reg the pump will destroke??

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Old 05-29-2008, 03:12 PM
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The regulator you have will just choke down the flow to the required 6 psi for your carb. I installed the same pump and I believe they are only rated at like 12-17 psi anyways so it doesn't take much to get it down to 6 psi. I believe there is a spring and a baffle that only allows a certain amount to pass. And when that pressure is exceeded it restricts the fuel flow to even out the pressure. I know that holley provides that regulator with their pumps but I switched mine to a return style regulator.

This allows the pump to run freely without fuel pressure backing up against the pump which may cause it to run hot and burn out faster.

I have been running this pump on a BBC for awhile and recently changed it to a SBC and it has performed very well for both.
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Old 05-29-2008, 04:12 PM
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You would be wise to run it through a relay rather than a direct wire.

Chet
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Old 05-29-2008, 04:17 PM
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Quote:
Originally Posted by T-bucket23
You would be wise to run it through a relay rather than a direct wire.

Chet
Copy that Kemosabe.
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Old 05-29-2008, 08:30 PM
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I know it would be wise but I am not very electrically enclined so I think I am going to go with the easy way out on this one So if I do wire it through an ignition 12 volt source I am still confused on how the pump prevents overpressuring?? Will it always be running?? In other words how does the regulator stop the the pump from pumping is my question.
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Old 05-29-2008, 08:42 PM
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The pump will not stop pumping

Whether it be a vane type pump or a diaphram type pump, they are designed to 'hold' xxlbs of pressure.

The mechanical pump on the car is always pumping---much more than can be used by the engine----but once it reaches a certain pressure---it cannot pump any more----it just goes thru the motions.

I also have a bypass regulator on my in-tank electric pump.
Did it for a couple of reasons----one being able to keep the carb with cool fuel (So Texas resident). My return line starts at the carb and the regulator is on the return line near the tank.
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Old 05-29-2008, 09:13 PM
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Quote:
Originally Posted by sexypizzaman
just installed a holley electric blue fuel pump in my car (came stock with a mechanical pump). It came with the regulator since I am running a carb, my question is when i wire the fuel pump up (to a 12v switched ignition power source) won't the pump ALWAYS been running as long as the key is switched to ignition?? The regulator doesn't have a return to tank or any electrical connections just 1 in and 2 out so how the hell does it regulate anything if the pump is constantly running?? By lowering the pressure of the regulator how does this stop the pump from running if the key is turned to ignition?? I am really confused on how all of this works because I know for a fact that by wiring the pump this way it will be running all the time the car is thus creating way too much pressure and flow?? Can somebody please clear this up for me. Maybe it is a variable displacement pump and by chaning the pressure at the reg the pump will destroke??
The regulator is pressure and flow sensitive. It has an internal variable flow valve that can move from off to whatever will hold 6 PSI or what ever it's set for. When there is flow on the carb side it opens enough to to maintain 6 PSI, unless the engine can suck so much fuel out of the float bowl that at 6 PSI the regulator can't keep up with demand at that point the engine leans out and starts to backfire. When there is no flow required by the carb, such as pump running with the engine not, the regulator closes completely preventing fuel pressure from exceeding 6 PSI on the carb side. On the other side (pressure) of the valve, the pump is dead heading against however much line pressure it can develop. This isn't a really good situation for the pump but since the stall head pressure is only 12 PSI in this case, it isn't hard to design a pump to tolerate that pressure. Going to higher pressures such as found with EFI systems requires a bypass to eliminate overheating the pump impeller and the surrounding fuel.

Bogie
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Old 06-11-2008, 04:54 PM
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fuel pressure help needed

I converted my 78 elk to a TPI fuel injected 350 and I an using an external MDS 225 electric fuel pump. It has been working fine for over a year, last week I started blowing fuel regulator gaskets, its making 100 psi of fuel pressure. The return line is not blocked, I don't get what is causing it. If the pump went bad wouldn't it push less? Help please
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Old 06-11-2008, 05:35 PM
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Quote:
Originally Posted by 78ELK51GMC
I converted my 78 elk to a TPI fuel injected 350 and I an using an external MDS 225 electric fuel pump. It has been working fine for over a year, last week I started blowing fuel regulator gaskets, its making 100 psi of fuel pressure. The return line is not blocked, I don't get what is causing it. If the pump went bad wouldn't it push less? Help please
The MDS-225 is only rated to 40 psi. How it's doing 100 seems improbable, especially with a return. It's a centrifugal impeller type pump, the only way it could develop that much pressure, would be if the motor was considerably over speeding. I'd check voltage at the pump as a DC motor's speed is directly proportional to voltage. The only other thing I can think of is that it has an internal resistor that somehow has become a conductor. There could be a load sensing switching mechanism that has failed and has the motor on all the time. I've never taken one of these apart so I'm not speaking from design knowledge only from what I presume to expect is in there based upon the failure you're reporting.

If it weren't for the blown diaphragm in the regulator, I'd attribute this to a failed pressure gauge, but the blown diaphragm is a big indicator that what you're reading on the gauge is really there. I'd really pull that pump soon as the system isn't designed for that kind of pressure, I expect the possibility of becoming the owner of a barbecued El Camino is really high.



Bogie
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Old 06-11-2008, 07:13 PM
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Why do you want to run an electric pump? Mechanicals fed some of the biggest engines to ever come out of Detroit. Hemi 426, L-88 427, LS-6 454, Cobra Jet, etc. Do yourself a big favor and put a high flow mechanical on there and don't look back. One less electrical circuit to worry about, no noise, no carb flooding due to cheap regulators, I could go on and on. There is absolutely no reason to put an electric pump on a street driven car unless you have a newer engine and the mounting pad is not there, or you are running fuel injection.
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Old 06-11-2008, 07:52 PM
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Quote:
Originally Posted by cool rockin daddy
Why do you want to run an electric pump? Mechanicals fed some of the biggest engines to ever come out of Detroit. Hemi 426, L-88 427, LS-6 454, Cobra Jet, etc. Do yourself a big favor and put a high flow mechanical on there and don't look back. One less electrical circuit to worry about, no noise, no carb flooding due to cheap regulators, I could go on and on. There is absolutely no reason to put an electric pump on a street driven car unless you have a newer engine and the mounting pad is not there, or you are running fuel injection.
He's running TBI injection and needs about 40 psi, mechanical fuel pumps don't deliver that kind of pressure.

Bogie
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Old 06-12-2008, 04:56 AM
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With the regulator that came with my blue pump if the eninge is not running and the pump is on the pressure will continue to rise untill it buries the needle on the gauge. Is that a by product of a "deadhead" setup?
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Old 06-12-2008, 05:12 AM
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Thanks!

Thanks Guys, I decided to replace the pump. It is connected to a relay that only runs when the ignition is on and does turn off when pressure is up and the engine is not running.

If this doesn't work, maybe a 800 HP motor can use the fuel - oh wait -gas is 4.25 a gal.
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Old 06-12-2008, 06:51 AM
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Quote:
Originally Posted by cool rockin daddy
There is absolutely no reason to put an electric pump on a street driven car unless you have a newer engine and the mounting pad is not there, or you are running fuel injection.

There are plenty of reasons to run an electric pump on a carb,

They are easier to replace, they can be mounted anywhere, they don't wear down your camshaft, your cam may not even have provisions for a mechanical fuel pump. They look cool hanging out under the frame with a big chrome fuel filter.

And personnally I like to turn the key on and listen to it "spool up" before lighting the fires on the Big Block. You should see when people are walking by on the sidewalk they will pause for just a second when they hear that whine and then "BOOM" it is like the preamble to a symphany.
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Old 06-12-2008, 07:06 AM
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A holley blue pump that turns off when the pressure is up?? Never hear of that. That pump should be set up to run when the key is on and shut off when the key is off. You can also use an oil pressure switch to active it. And those pumps should be mounted by the gas tank and as low as possible. Those are loud pumps, get a mallory comp110 if you want quiet.

78elk,
A MSD 2225 efi pump can make 100 psi if you pinch off the return line. Most efi pumps can make that kind of pressure as long as there is no flow. If the return line is open then there is a blockage in your regulator.
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