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electric fuel pump question

32K views 26 replies 14 participants last post by  vtown 
#1 ·
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?? :confused: :confused:
 
#2 ·
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.
 
#5 ·
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 :p 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.
 
#6 ·
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.
 
#7 ·
sexypizzaman said:
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?? :confused: :confused:
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
 
#8 ·
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
 
#9 ·
78ELK51GMC said:
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
 
#10 ·
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.
 
#11 ·
cool rockin daddy said:
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
 
#13 ·
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.
 
#14 ·
cool rockin daddy said:
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.
 
#15 ·
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.
 
#19 ·
Solution to problem

I have been meaning to post this but never got around to it. After replacing the new fuel pump I had to replace the regulator with a high performance one. That solved the problem. My mechanic had been replacing the regulator with a stock one which kept blowing out. The High perf regular can handle more pressure. No problems since. Reading some of the posts I noticed people thought I had a carb. or could use a mechanical pump. This is a tuned port fuel injection setup from an IROC, it calls for higher pressure than a mechanical can use, the extra gas returns to the tank. From what I read this is the way to retro fit the car. I like benefits of the fuel injection, but i wouldn't do it over again. Thanks All!
 
#20 · (Edited)
sexypizzaman said:
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 :p 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.
First of all, wiring in a relay is super simple. Do it right or it will leave you stranded. Not using a relay because you don't know how to wire it is like not using a postage stamp because you don't know which side to lick. Just ask.

Secondly, the pump will run as long as the switch is on. The regulator's job is to regulate how much pressure makes it past and gets to the carb. If you put a 90 psi pump in the tank and used a regulator to step it down to 5 psi for a carb, it would only deliver 5 psi to the carb. That's how regulators work. Regulators are like bouncers at a busy club. The club is the carburetor, the bouncer is the regulator, and the 500 people waiting in line are the pressure from the pump. It doesn't matter how many people want to get in, the bouncer only lets 200 in at a time. As the people leave the club, the bouncer lets a few more in. Same thing in a car. The pump supplies excess pressure, the regulator only lets 5 psi through. As the carb flows fuel into the engine and leaves a void, the regulator lets more fuel through and keeps the pressure at 5psi. At wide open throttle, the regulator is flowing alot to keep 5 psi, but at idle, it only has to flow a little bit.

For instance, lets say you run the pump while the car is off. The regulator will let enough fuel through to put 5 psi in the line to the carb, then it shuts the door. Now start the engine. As fuel flows out of the carb and the floats open the valve, the regulator notices that the pressure has dropped and it opens the door a bit to keep up with the requirements. The pump keeps pumping, but there is no fuel moving. Its just spinning its wheels.

If you want the truly best way to wire it (in my opinion) do it this way. Test your oil pressure switch for the dummy light.

If it grounds when it has pressure and doesn't ground when it doesn't have pressure, do this: Use a SPST relay. give post 85 switched power through a small (1 amp maybe) fuse. In fact, your fuse block should have a post that says "accy" that is already fused by the fuse to the left of it. Pre wired for you :) Wire post 86 to the oil pressure switch. The wires on 85 and 86 can be very small, like 18ga. Then from the battery through a fuse for the rating of the pump to post 30. Then from post 87 to the fuel pump's + side and ground the - side.

If your oil pressure switch grounds when you have no pressure, do this: Use a DPDT relay. The only difference is that you don't use 87 to go to the pump, use 87A to feed the pump. Everything else is the same.

When you wire it this way, the pump will only run when oil pressure is present. This does two things; First, it only makes the pump run when the engine is running, and 2, if you lose oil pressure, you lose fuel and the engine shuts down to save itself. If you don't wire it like that, the pump will run whenever the key is on, deadheading against the regulator. That means the pump will be running, but not moving fuel and it is hard on the pump. If you ever run out of gas, or if you drain the carb for repairs, all you have to do is turn the key on, take the wire off the oil pressure switch and ground it for a couple seconds. That will run the pump to fill the carb.

A relay is just a remote switch. All you are doing is sending power to the pump through a tiny black box. you use a small wire that simply turns on the power when you want it to. As it is, your steering column already has wires that carry relatively large amperages; turn signals, windshield wipers, starter, all of the accessories. Adding a fuel pump (or any other accessory) will be adding how much amperage gets drawn through the wires from the switch. If you add a relay, you're only adding about 1/4 of an amp to that wire and letting the heavy wire from the battery handle the load for the pump. The accessory circuit in the car uses 14 ga wire. Everything that only works when the key is on is designed to draw amperage through that wire. If you add a significant amount of load by just tapping into the accessory circuit, you run the risk of overloading that circuit, causing headaches, melted wires, and in the worst case, a fire. Ask me how I know. I ripped a dashboard out with my bare hands and unloaded a fire extinguisher in a 66 Bonneville for that exact reason.
 
#26 ·
The pump needs to run all the time the engine is running. I like to switch the pump independen of the ignition so it the ignition is on but the enigne not running the pump can be off.

A bypassing regulator will quiet the pump by relieving it from pumping more fuel than the enigne is using. They rattle when deadheading not that this is actually dedheading by the definition but the pump runs at one speed and one delivery when the engine uses less than that amount of fuel the pump is pushing against the built up pressure which is it's max output this rattles the impellor making a lot of noise.

Bogie
 
#21 ·
fuel pump electric

I have a newer engine in my 1939 chevy sedan a 350 no port for mechanical pump so i put in electric one a holly red i wired it to my ignition switch manufactor said did not require a regulator it runs all the time same speed even at high rpm and is a noisy son of gun a friend told me it should only run at start up and when it reaches max presure should shut off what did i do wrong
 
#22 ·
I have a newer engine in my 1939 chevy sedan a 350 no port for mechanical pump so i put in electric one a holly red i wired it to my ignition switch manufactor said did not require a regulator it runs all the time same speed even at high rpm and is a noisy son of gun a friend told me it should only run at start up and when it reaches max presure should shut off what did i do wrong
Your friend is wrong, the Holley pump will run continuously. It has an internal bypass, once the pump makes 7 psi line pressure the pump begins to bypass fuel inside itself.

The only pumps that do what your friend said are stock inside the tank pumps on fuel injected vehicles.

There is nothing wrong with your set-up.
 
#23 ·
#25 ·
Carter electrics, I think 4070 is the part number is about the lowest cost that is reasonably quiet, then Mallory Comp 110 and Comp 140 and Holley Billet 150....the 110, 140, and 150 are gearotor pumps instead of vane pumps, vane pumps are very noisy(Holley's Red, Blue, and Black are vane pumps).

Mounting a vane pump in rubber isolation bushings(donuts) helps quiet them down. Carter #1814U isolator kit
 
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