electric fuel pump

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Electric Fuel Pump: How to Do It Right

Want an electric fuel pump to last forever and work right? We're going to show you howto install it and wire it up the correct way!

Ok, let's talk about electric fuel pumps. There is a lot of confusion andmisunderstandings about them. There is also alot of potential danger when people don'tdo it right because they don't know the right way to plumb them in or wire them...

So, let's break it down:

When do you need an electric fuel pump?

Is an electric fuel pump reliable?

How do you keep an electric fuel pump safe?

How should you wire an electric fuel pump?

-When do you need an electric fuel pump?

Usually, a mechanical pump is preferred over an "aftermarket" electric pump. They tendto be more reliable. However, sometimes that won't work.

In my old '47 Chevy, the engine I had swapped in had an issue. The crossmember was inthe way of the mechanical pump. So, I ran an electrical pump and had many trouble freemiles.

Sometimes, people will plumb them inline with a mechanical pump to add more volumeand pressure. This is more for a full on drag car though...

-Is an electric fuel pump reliable?

Yes they are. Hey, there's about a billion cars running around right now with them. Allnew cars have them.

With aftermarket pumps though, YOU have to install them. That's where some problemscan start.

We're here to show you the right way to do it!

So, what do I use? For a stock or performance street car, I like these Facet/Purolatorpumps from Napa. They are quiet, and work well.



Alot of people complain about some aftermarket pumps being junk, but usually there is areason they go out. It's often the way the person installed it. There are a few things thatkill them.

-Do not run them dry.

-Always run a filter before the pump.

-Keep them as close to the tank as you can. Electric pumps push fuel much better than

they can pull it.

-Mount them away from heat sources such as exhaust.

-Electrical power to them is everything. You must have the correct wire size to it. A relayis preferred. You may be getting the proper voltage to it, but not enough amps.Remember, the longer the run the more the power will drop.

-Also, the grounding of it is critical. Many people will scrape the area where they mountit, or even add a ground wire. However, they forget that they don't have a good groundfrom the body to the frame or to the engine. This will kill pumps real quick.

Tip: Screw into metal to ground, not through it. "Star" washers are your friends...

Preferably, run a ground wire to the front. Many professional auto electricians will runground wires from a unit to a common grounding point in an older car, just like in afiberglass car. That way, there is no question if your ground is good, and it's just 1 extrawire...

Once, a buddy and me were going to a show in his '26 Buick roadster. It was built muchlike a T-bucket and it had an electric fuel pump. It was wired in correctly, and groundedby screwing into the frame by the pump. We were about 50 miles out, and the pump

quit...

Hmmmm...

What happened was the older metal of the frame simply wasn't carrying the current wellenough. The pump overheated and shut down.

Fortunately, he had some extra wire and we screwed one end to the ground wire at theback and ran it to the front where we attached it to the negative side of the battery.

The pump started back up after it cooled down and we were trouble-free all the way

there and back. When we got home he wired it in neatly and never had a problem afterthat...

-How do you keep an electric fuel pump safe?

Electric fuel pumps can be dangerous?

Yep, without some way to automatically shut them off, they can be VERY dangerous.

But they don't have to be.

If something lets go in your engine bay like a fuel line, the engine will eventually quit.However, if you don't have a way to automatically shut off your electric fuel pump youwill keep spraying raw fuel all over your hot engine and wiring.

Also, in a crash, your pump can continue to run feeding a fire if you don't have a way tostop it.



Note: Never mount an electric fuel pump in an enclosed area such as the trunk orinterior space...

Ok, so how do I do it right?

The easiest way is to use an oil pressure switch. The switch will stop the pumpwhenever the oil pressure in the engine goes away. So, whenever the engine is off, thepump will turn off automatically.

Some switches just do that. But how do I get the pump to run when I'm trying to startthe motor and the oil pressure's not up yet?

You use a three prong switch like this Standard Ignition PS-64:

The switch will also let the pump run when you hit the starter because the enginedoesn't have oil pressure yet.

One wire goes to the pump, one to the start circuit, and the other to the ignition circuit.So, when there is no oil pressure, the switch connects START to PUMP, and as soon asyou start cranking it runs the pump. When the oil pressure comes up, the switchconnects IGN to PUMP, for normal running. When oil pressure goes away (because youjust hit that rock and tore the pan off the engine, for example) it again connects STARTto PUMP, and disconnects IGN from PUMP, so the pump shuts off.

Don't worry, it's easy to wire...

-How should you wire an electric fuel pump?

Since you need the fuel pump back by the tank and at the same level as the fuel orlower, that usually means you're going to have a long run of wire. So, you need to have



really good wiring going back to it. Wiring that will carry enough current. Running thecurrent through your ignition switch isn't a good idea since it's probably alreadyoverloaded, and will kill the voltage. That will kill the pump. However, it's nice forconvenience. That's why a relay is really good to use.

It lets the ignition switch activate the pump, while keeping the power from having to runthrough it. It will keep your pump alive and happy because it is getting full voltage. Agood way is to mount a relay beside a power distribution block on the firewall (seeImproved Power Circuit) and get the power from there.

Here is a diagram on how to wire and plumb your pump:

How Does a Fuel Pump Relay Work?

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How to Tell If You Need a New Fuel Pump

How to Check a Fuel Pump Relay Switch

. Startupo A fuel pump relay takes control of the fuel pump during engine startup, but shuts itself off after

the engine is running. An oil pressure mechanism resumes control of the fuel pump after the fuelpump relay shuts off and the vehicle's engine is running. The oil pressure mechanism also relaysoil pressure data to the gauges on the inside of the driver's dashboard. The vehicle will not start,however, if there isn't enough oil pressure to generate the electricity needed to run the fuel pump.When the oil is warm, it becomes thinner, making it difficult to pump into the engine. The fuelpump relay generates a humming sound when the ignition is turned on. When the hummingsound is not audible, it is time to have the fuel pump relay replaced by a mechanic. The starter cranks are charged up by a cold start valve, which is operated by the thermo timing switch. This

valve injects fuel when heat is at a minimal level. While cold start valve is operating, the thermotiming switch heats up (while cranking). The cold start valve will stop injecting fuel if the enginefails to start after prolonged attempts to start the engine (this is done to avoid flooding the enginewith fuel).

Components

o Each fuel pump relay has a magnetic coil with an open contact. The relay charges up when theignition is started. The magnetic coil's open contact clamps shut, closing the circuit between thefuel pump relay and terminal that leads to the electronic control mechanism. A ballast resistor bank receives an electrical charge through the same terminal as the control mechanism. A switchtransistor housed in the control mechanism is wired to all injector solenoids. The ballast resistorsact to quicken the time it takes for injector solenoids to respond.

o

Two Relays

o In some vehicle designs, there are two fuel pump relays (with one of the fuel pump relay unit'scoils running to a diode). The diode is designed to keep electrical current from flowing in theopposite direction (backward). The electrical current runs through the starter solenoid and one of the fuel pump relay terminals. As the engine runs for a while, the air flow sensor executes apump switch that closes the terminals to the fuel pump relay. The terminal leading to the starter isde-energized. The first fuel relay contains a resistor that maintains enough current to ensure therelay stays electrically charged up. This design ensures that the fuel pump will shut down in theeven that the engine should stall.

Customer Question

93 chevy g 20 van no power to the fuel pump relay and no power to the fuel pump. I tested the wires. I had

someone turn on the key while I tested the wires at the relay and at the pump. No power. I checked thefuses and the computer fuses. There is no fuel cut off switch as far as I know. Does the computer in thisyear control this and is the computer shot

Country: United StatesMake: ChevroletModel: G20 SportvanEngine: 350

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The computer supplies power to the fuel pump relay, and the relay is always grounded. Do you have aschematic for the fuel pump relay and fuel pump?

no I tried to find one on line . The van quit and i started at the fuel pump and worked my way under thehood and the traced the gray black and green wire from the relay to the computer behind the driver seat

OK, let's start with a schematic so we're both talking about the same thing.

These diagrams are tough to follow from those days, the layout wasn't great. But essentially, you shouldhave power on the orange wire at the fuel pump relay as well as at the oil pressure switch. Do you havepower there?



yes orange wire is hot all the time key on or off. there is an orange wire, a gray wire, a black wire, withwhite strip, a green wire with white strip, and a red wire that end to an unused connector

OK. That's good. On the red wire with the unused connector, put power to that connector from the battery.The pump should run. Does it?

I will try it take me a little time to dig up a wire The relay is brand new that was the first thing I changedbecause I put a new fuel pump and sending unit in about a month ago It ran great until Friday when it quit

so i changed the relay then i thought the new pump was bad but first i checked for power . At the pumpthere is a black wire which i believe is ground and a gray which I believe is power and a purple wire whichgoes to the float. I get power to the purple but nothing from the other 2 wires when the key is turned on i

know you have only a few seconds to test it before the relay cuts it off. From the relay or to the relay isthose other wires Is there something on the engine or distributor that could be shutting down the pump??or the computer??? I will try the red wire to see if that works

120 is the gray wire that goes to your pump. The red wire with the unused connector is a fuel pump primelead, it's there for exactly what we're doing: running the pump manually. 340 is the orange wire that's hotwith the key on. Black with a white stripe is circuit 450, that comes from the ECM. It should be grounded,

it's an ECM ground. 465 is the dark green and white wire, this also comes from the ECM. ECM puts power tothis wire for 2 seconds at key on, then it doesn't power it again until it sees the engine turning over.

That's all of the wires. You should be able to check those with a test light and a jumper wire, and figure outwhat's wrong with the circuit.

I jumper the red and no fuel came up to start the engine. The tank is on the ground but everything isconnected. So you are telling me that the green wire powers up for 2 seconds. My wife turns the key on andoff for me while I test the wires. The orange is hot when the key is off or on. I get nothing from the greenwire at all. So the gray suppose to go back to the pump along with the black but it goes first to thecomputer. Is the computer messing this all up??

One thing at a time. No matter what else happens, when you put power to the red unused connector the fuel

pump relay, that pump should run. That puts power directly through the relay and to the gray wire, whichgoes to the pump. Let's work out one thing at a time. There has to be continuity on the gray wire from therelay to the pump. Do you have an ohmmeter so you can test that?

No ohmmeter.When i connected the red wire it sparked. My wife connected the red wire and i went back tothe tank and listened. The pump made a clunking sound she connected and diconnected as I instucted I had

my ear on the tank The pump clunked but didnt hum then for just a moment it hummed and stopped rightaway. I wonder if the pump is shorting out or maybe I have more than one problem. Like i said with the plugdiscoonected at the tank the only power comes from the purple float wire the gray and black nothing. Igrounded to the frame. If the red wire makes the pump run how do I fix the problem so it works like itshould?? Oh and I realy appreciate you patiance This is driving me madd

are you still working with me does the fuel pump oil pressure switch and sender affect this?

I see that the relaypowers to the pessure switch I wonder if the pump went bad and at the same time itaffects the ecm instant cut off I dont like all this computer junk and I know it is getting worse. I will takeback the pump and get a new one but then I need to know do I need a computer /ecm. if it still wont run

Sorry I stepped away for a couple of hours. I'm still with you on this.

I think you have a bad pump, provided your pump ground is good at the frame. It's hard to pinpoint withouta multimeter, but if you put power to the prime connector and the pump tried to run, it's probably gettingpower and it's just no good.

Don't over think the oil pressure switch. Its only function is to run the fuel pump in case the fuel pump relaygoes bad. Oil pressure has nothing to do with normal pump operation.

Check the pump ground at the frame, make sure that's clean and tight. Then yes, replace the pump, and let'sstart again with a fresh pump.

You are just perpetuating a myth popular with newby owners.

Only have to look at the circuit diagram which obviously you haven't or don't understandto see that taking the OP switch out of operation ( from low oil pressure ) has no effect on pump

because the OP switch is wired in parallel with the pump relay which is closed and also sendingpower to the pump anytime engine is running



How To Wire Cooling Fans, Headlights, Fuel Pumps & Voltmeters -

Custom Wiring You Can DoBy Marlan Davis, Photography by Mark Hamilton, Marlan Davis

Car Craft, March, 1999

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Are your old musclecar's headlights too dim? Want to add a new high-current accessory without overtaxing the existingelectrical system? Perhaps you need to activate an electric fan or nitrous system by means of an automatic switch. You could

accomplish these tasks by rewiring the entire circuit using heavy-gauge wire, but that's time-consuming, adds needless weight,and is electrically inefficient. A far better solution is to use a relay.

A relay is a type of heavy-duty remote-control switch able to handle high-current accessories, yet capable of being actuated by

substantially less current. Relays are installed between the power source and the electrical accessory requiring on/off power.When the relay is energized (turned on), the high current required to operate the accessory flows from the power source,through the relay, and directly to the part.

Supplying high-current devices requires heavy-gauge wire; the longer the circuit the larger the required conductor diameter. In

12-volt automotive electrical circuits, even small amounts of resistance can cause significant amounts of voltage drop. Circuitswith long wire length and multiple switches and connections inevitably have a certain amount of voltage drop caused by normalresistance buildup; deterioration from vibration, high temperatures, and corrosion only compound the problem. Relays provide asolution by shortening the required length of the heavy-gauge power delivery wire from the battery or alternator to the load.

Relays are typically energized through an operator-controlled dash-mounted switch, or by remotely mounted pressure-,vacuum-, or linkage-actuated switches. With only a small amount of current needed for the relay-actuation side of the circuit,

you can use a low-amp on/off switch and small-gauge wire (even on long runs) to connect the on/off switch to the power source

and relay. The diagrams on these pages show just some of many typical relay uses, as well as how to hook up the universal ISOrelay sold by M.A.D. Enterprises, Jacobs Electronics, and other electrical suppliers.

Using a relay as a heavy-duty remote-control device ensures delivery of full power to high-load electrical components: Your

headlights will burn brighter, your electric fan will run faster, and fuel pumps will operate at their peak efficiency. Voltage dropat the dash harness is reduced, and overall switch and electrical system performance and longevity are enhanced.



A relay is a heavy-duty, remote-control electromechanical device that supplies direct high

ISO relays are compact in design and easy to mount. The same basic relay design can actuat

Compact universal ISO relays have become a generic part. The terminal pattern and the numb

How It Works

This diagram illustrates the function and operation of the versatile ISO-style "1 Form C single pole/double throw" (SPDT) relay.It can be used to control both normally open (NO) and normally closed (NC) circuits, or it can act as a change-over device toswitch current from one user to another. The low-current switch controlling the circuit sends current through the pull-in windingterminals (85 and 86). This energizes an electromagnet that pulls a movable arm, closing the NO high-load circuit (30 to 87).When the controlling switch stops current from passing through the magnetic winding, spring action pulls the movable arm inthe opposite direction, completing the NC high-load circuit (30 to 87a).

The ISO relay's high-load circuits are rated at 40 amps NO/20 amps NC for resistive loads, and 20 amps NO/15 amps NC forinductive or lamp circuits. Other ISO relay variations may have only NO or NC circuits, but because of the terminals' universalnumbering scheme, you can always figure out their function and how to wire them.

Cooling Fan M.A.D. likes to use two relays to power up one large electric cooling fan. Even though the ISO relays are rated at 20 amps for

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this application, experience has shown a large fan motor will overheat a single relay. Installing two relays in parallel removesstress loads from each relay and improves reliability with redundant parts. (One relay per fan is sufficient for systems with two

small fans.). Fans' relays are typically actuated via an engine- or radiator-mounted thermostatically controlled switch, but youmay wish to install an extra manually operated switch on the dash as a fail-safe device.

Many GM cars use this proprietary relay (GM 14103304) to actuate the coolant fan(s). The r

Headlights Mounting relays near the front of the car makes it easy to route high-amp current directly to the headlights. The factoryheadlight switch and beam-select switch need only energize the relay for it to send full battery power into the front lighting

system harness. This removes the load from the dash harness and is recommended for old under-wired musclecars or anyvehicle upgrading to high-power halogen lights.

This '65 El Camino's factory wiring was OK, and it had a modern integrally regulated alter












After upgrading the lighting circuit with relays, there were 14.0 volts at the battery and

Fuel Pump This circuit delivers maximum current to the fuel pump and enhances safety by using a factory GM oil pressure switch. With theignition in "run," engine oil pressure closes the switch to complete the circuit from terminal "I" to terminal "P," which deliverspower to relay terminal 86 and to the ground via terminal 85. This energizes the relay, allowing battery positive power to flowdirectly through terminals 30 and 87 to the fuel pump. When the engine stops running, oil pressure drops, the switch opens,

and the relay de-energizes. This provides automatic fuel pump shutdown after a crash or engine failure, and also prevents the

fuel pump from running if the ignition is left on. Wire the pressure switch's "S" terminal to the ignition "start" circuit to providefuel pump pressure during engine cranking, and/or prime empty carb float bowls.

Mount the relay as close to the battery as practical, and install a fusible link two wire-gauge sizes smaller than the high-amp

power feed fire. Wire the pressure switch using generic 1/4-inch female-blade terminals or a three-prong, weather-resistant,molded-on, 56-series connector assembly: GM 12101928 (AC-Delco PT200) has a black PVC connector-shell; slightly more

expensive GM 12085529 (AC-Delco PT139) has a high-temp TPE shell.

This oil pressure switch was used on many GM applications. It's available from several sou

Voltmeter Many cars experience voltage drop in the main-feed wire that delivers power to the dash area. The more dash switches that areturned on, the greater the power drop. This can cause the voltmeter at the dash to display a significantly lower voltage than theactual battery voltage. You may think there's a problem with alternator output, when in fact the alternator is working fine. The

voltmeter can be made to show exact battery voltage by wiring up a relay as shown here. Be sure to route the wire from relayterminal 30 directly to battery positive, and that no other circuits use this wire.



















If the voltmeter reads way low at the dash, but an output check at the alternator shows the device is operating normally (14volts or higher), add a relay so the voltmeter reads accurately.

If the voltmeter reads way low at the dash, but an output check at the alternator shows th

The horn relay on '60s GM cars serves as the main power distribution point for the whole e

Relay kits are widely available from electrical specialists like M.A.D. Enterprises. M.A.D

















electric fuel pump

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