Fuel Pump Operation

Gojuu · Apr 22, 2022

Hi All, hoping someone can help with this.

Can someone tell me if there is any for of pressure sensor or similar in the fuel pump? When I switch on my bike I hear the fuel pump run for a few moments before it stops. Is it stopping because it has reached a certain rail pressure? Or does something else control that initial run time?

Voodooo · Apr 22, 2022

Gojuu said:
Hi All, hoping someone can help with this.

Can someone tell me if there is any for of pressure sensor or similar in the fuel pump? When I switch on my bike I hear the fuel pump run for a few moments before it stops. Is it stopping because it has reached a certain rail pressure? Or does something else control that initial run time?

It’s reached it’s pressure

Stu Bodycote · Apr 22, 2022

Timer, they run for around 3sec to prime. If they ran until pressure was attained, then my pump would soon burn out as Ive yet to put fuel in the Tab tank.

TonyA · Apr 22, 2022

Stu Bodycote said:
Timer, they run for around 3sec to prime. If they ran until pressure was attained, then my pump would soon burn out as Ive yet to put fuel in the Tab tank.

I thought Voodoo was able to pump out his tank by attaching a hose to the pump spigot and ran the hose to a gas can and then applying power to the pump. I saw there is a pressure regulator in the fuel pump assembly . But I think this just bleeds off excess fuel back to the tank . They say not to run your fuel pumps when dry.

Gojuu · Apr 22, 2022

Voodooo / Stu - is it 3 seconds or until pressure is attained - or a bit of column A and B?

Maybe I'll ask a different way, should the pump start every time the bike is turned to on for 3 seconds - or if it has rail pressure does it not run?

City Garage · Apr 22, 2022

TonyA said:
I thought Voodoo was able to pump out his tank by attaching a hose to the pump spigot and ran the hose to a gas can and then applying power to the pump. I saw there is a pressure regulator in the fuel pump assembly . But I think this just bleeds off excess fuel back to the tank . They say not to run your fuel pumps when dry.

Yes this is correct. But the ECU triggers the relay so that how the initial ignition turn on works. Then if under pressure like you turned key off them back on the pressure would bleed off from regulator

City Garage · Apr 22, 2022

Gojuu said:
Hi All, hoping someone can help with this.

Can someone tell me if there is any for of pressure sensor or similar in the fuel pump? When I switch on my bike I hear the fuel pump run for a few moments before it stops. Is it stopping because it has reached a certain rail pressure? Or does something else control that initial run time?

as Stu said. you can see this in the ECU programming. Also at the same time the injectors open for a split second to give the initial prime of fuel to start the bike. again this can be changed by the ecu

City Garage · Apr 22, 2022

Gojuu said:
Voodooo / Stu - is it 3 seconds or until pressure is attained - or a bit of column A and B?

Maybe I'll ask a different way, should the pump start every time the bike is turned to on for 3 seconds - or if it has rail pressure does it not run?

Yes every time you turn on the key the pump will run at first. Excess pressure if any will bleed off from the regulator. This is how the bike is set to start.

Gojuu · Apr 22, 2022

City Garage said:
Yes every time you turn on the key the pump will run at first. Excess pressure if any will bleed off from the regulator. This is how the bike is set to start.

@City Garage - so the ecu closes the relay, opens it after the time it is programmed to "prime" for, then closes it again when the bike starts?

TonyA · Apr 22, 2022

Gojuu said:
@City Garage - so the ecu closes the relay, opens it after the time it is programmed to "prime" for, then closes it again when the bike starts?

After looking at the drawing , One end of the fuel pump relay coil goes to the ECU . So the ECU can control when the fuel pump relay turns on or off.

Gojuu · Apr 22, 2022

Thanks all - very helpful as always.

Voodooo · Apr 22, 2022

TonyA said:
I thought Voodoo was able to pump out his tank by attaching a hose to the pump spigot and ran the hose to a gas can and then applying power to the pump. I saw there is a pressure regulator in the fuel pump assembly . But I think this just bleeds off excess fuel back to the tank . They say not to run your fuel pumps when dry.

I fitted a connector to my fuel pump fitting with a hose attached. Then I used a switched relay. It’ll pump until you turn it off. But when the fuel system is closed, the pump stops when fuel psi is reached. That only takes a few seconds. I’ll agree it won’t keep running non stop, but to prime the system only takes seconds. In which it also reached its fuel psi.

Also, with the switchable relay, they key is in the off position, the switch on the relay is what controls the fuel pump. When I drain my tank, I attach the hose to the fuel pump, turn on the relay (ignition key off) and the pump will run for as long as you have the fuel pump relay on. Or until you’ve run the tank empty and burn up the pump lol.

Gojuu · Apr 22, 2022

Voodooo said:
I fitted a connector to my fuel pump fitting with a hose attached. Then I used a switched relay. It’ll pump until you turn it off. But when the fuel system is closed, the pump stops when fuel psi is reached. That only takes a few seconds. I’ll agree it won’t keep running non stop, but to prime the system only takes seconds. In which it also reached its fuel psi.

Voodooo - I get what you’re saying.

I think the answer is a bit of both. After @City Garage mentioned the ECU control (and then @TonyA ) I looked in the ECU and it's there:

I suspect what happens is that (and I'm not sure about a part):

Key switch and the ECU gets an on signal
The ECU closes the fuel pump relay to prime for the value set of 3 seconds (as above)
The part I'm not sure about is that even though the relay is closed and supplies power to the fuel pump, there is something installed that can still sense the rail is at pressure and not start the pump (and is this done at the pump?)
This also makes sense as if you turned the ignition on and the pump just ran (rather than the ECU set 3 seconds) it could burn out/fail on a dry tank (as Stu says)
Once the bike goes to cranking or running the fuel pump must be set to start?

Voodooo · Apr 23, 2022

Gojuu said:
Voodooo - I get what you’re saying.

I think the answer is a bit of both. After @City Garage mentioned the ECU control (and then @TonyA ) I looked in the ECU and it's there:

View attachment 94552

I suspect what happens is that (and I'm not sure about a part):

Key switch and the ECU gets an on signal

The ECU closes the fuel pump relay to prime for the value set of 3 seconds (as above)

The part I'm not sure about is that even though the relay is closed and supplies power to the fuel pump, there is something installed that can still sense the rail is at pressure and not start the pump (and is this done at the pump?)

This also makes sense as if you turned the ignition on and the pump just ran (rather than the ECU set 3 seconds) it could burn out/fail on a dry tank (as Stu says)

Once the bike goes to cranking or running the fuel pump must be set to start?

I never looked at the ECU parameters on our bikes, but with many OBD 2 automotive ECU, the crank position sensor and in some cases, the oil pressure sensor controls the fuel pump.

Once the ECU gets a signal that the engine is at a met RPM or Oil pressure, it will command the fuel pump to be turned on to supply fuel to a running motor.

TonyA · Apr 23, 2022

Gojuu said:
Voodooo - I get what you’re saying.

I think the answer is a bit of both. After @City Garage mentioned the ECU control (and then @TonyA ) I looked in the ECU and it's there:

View attachment 94552

I suspect what happens is that (and I'm not sure about a part):

Key switch and the ECU gets an on signal

The ECU closes the fuel pump relay to prime for the value set of 3 seconds (as above)

The part I'm not sure about is that even though the relay is closed and supplies power to the fuel pump, there is something installed that can still sense the rail is at pressure and not start the pump (and is this done at the pump?)

This also makes sense as if you turned the ignition on and the pump just ran (rather than the ECU set 3 seconds) it could burn out/fail on a dry tank (as Stu says)

Once the bike goes to cranking or running the fuel pump must be set to start?

Good Find ! An understanding of how our ECU/bike works is very helpful . The ECU can do quite a lot !

City Garage · Apr 23, 2022

TonyA said:
Good Find ! An understanding of how our ECU/bike works is very helpful . The ECU can do quite a lot !

Gojuu said:
Voodooo - I get what you’re saying.

I think the answer is a bit of both. After @City Garage mentioned the ECU control (and then @TonyA ) I looked in the ECU and it's there:

View attachment 94552

I suspect what happens is that (and I'm not sure about a part):

Key switch and the ECU gets an on signal

The ECU closes the fuel pump relay to prime for the value set of 3 seconds (as above)

The part I'm not sure about is that even though the relay is closed and supplies power to the fuel pump, there is something installed that can still sense the rail is at pressure and not start the pump (and is this done at the pump?)

This also makes sense as if you turned the ignition on and the pump just ran (rather than the ECU set 3 seconds) it could burn out/fail on a dry tank (as Stu says)

Once the bike goes to cranking or running the fuel pump must be set to start?

There is no fuel pressure reading for the ECU to modulate the fuel pump. it's on or off It's a simple system and relay controlled. The fuel pump is rated for volume and pressure, the injectors are rated for the volume/psi and the fuel pressure regulator controls the pressure by putting excess back into the tank. Once the motor is turning the fuel pump runs constantly. As Voodoo stated the add/loss of the RPM signal (think crank/cam sensor) turns the pump relay /onoff. That's all controlled by the ECU. You can see the pulse settings within the ECU for the injectors as well

So say you briefly turned off the bike to get the mail and the check valve in the fuel pump holds the fuel pressure that was in the rail when it was shut off. When you turn the key back on and the pressure is still the correct pressure the pump will still run as programmed but the pressure will bleed off from the pressure regulator which "senses" the rail is at pressure. That regulator is purely mechanical nothing electric. You can turn off and on the key a dozen times and it will still run as the ecu is programmed. (dont do that because it will flood the cylinders)

But the issue with my example above is that every time you turn on the key the injectors pulse to inject fuel into the cylinders at the same time so you lose some pressure initially but it's recovered in milliseconds as the pump runs.

Because you will probably ask the regulator is 3.5 or 50 psi. We have tested a few and they begin to open around 45psi

The injectors are rated at 43.5psi 3bar

Gojuu · Apr 23, 2022

@City Garage that's really clear.. Thanks.

My bike sometimes doesn't start, Normally - most of the time actually - it starts really easily and then out of nowhere just won't. Cranks very well, but simply does not fire.

And it doesn't start the pump every time I hit the key. And those times are when it doesn't start (surprise, surprise.....)

I've bench tested the relay, swapped the relay with another and can see the ECU output - both in terms of using SX tune to watch the value change and with a multimeter on the terminal it signals - so was looking for the next parts of the puzzle.

Thanks again to all of you that answered. A huge help as always.

Voodooo · Apr 23, 2022

City Garage said:
There is no fuel pressure reading for the ECU to modulate the fuel pump. it's on or off It's a simple system and relay controlled. The fuel pump is rated for volume and pressure, the injectors are rated for the volume/psi and the fuel pressure regulator controls the pressure by putting excess back into the tank. Once the motor is turning the fuel pump runs constantly. As Voodoo stated the add/loss of the RPM signal (think crank/cam sensor) turns the pump relay /onoff. That's all controlled by the ECU. You can see the pulse settings within the ECU for the injectors as well

So say you briefly turned off the bike to get the mail and the check valve in the fuel pump holds the fuel pressure that was in the rail when it was shut off. When you turn the key back on and the pressure is still the correct pressure the pump will still run as programmed but the pressure will bleed off from the pressure regulator which "senses" the rail is at pressure. That regulator is purely mechanical nothing electric. You can turn off and on the key a dozen times and it will still run as the ecu is programmed. (dont do that because it will flood the cylinders)

But the issue with my example above is that every time you turn on the key the injectors pulse to inject fuel into the cylinders at the same time so you lose some pressure initially but it's recovered in milliseconds as the pump runs.

Because you will probably ask the regulator is 3.5 or 50 psi. We have tested a few and they begin to open around 45psi

The injectors are rated at 43.5psi 3bar

I don’t know about the Norton, but on every vehicle I work on, the injectors don’t spray fuel into the cylinders until the engine is cranking or running. Not when the key is turned on.
You can’t flood the cylinders by cycling the key off and on, nor can you pump the gas, there’s no accelerator pump like a carb.

On the Norton, I tried to empty my fuel tank by connecting a fuel line fitting to the fuel pump outlet nipple, then cycle the key on, as you said, it’ll only pump a small amount of fuel for 3 seconds, that’s why I used a switched relay so I could turn the relay off and on to power the fuel pump to remove the fuel. This is done with the ignition key in the off position. The pump will run for as long as you have the relay on or until you burn up the pump after it’s empty lol.

City Garage · Apr 24, 2022

Voodooo said:
I don’t know about the Norton, but on every vehicle I work on, the injectors don’t spray fuel into the cylinders until the engine is cranking or running. Not when the key is turned on.
You can’t flood the cylinders by cycling the key off and on, nor can you pump the gas, there’s no accelerator pump like a carb.

On the Norton, I tried to empty my fuel tank by connecting a fuel line fitting to the fuel pump outlet nipple, then cycle the key on, as you said, it’ll only pump a small amount of fuel for 3 seconds, that’s why I used a switched relay so I could turn the relay off and on to power the fuel pump to remove the fuel. This is done with the ignition key in the off position. The pump will run for as long as you have the relay on or until you burn up the pump after it’s empty lol.

On the 961 there is a pulse when the ignition is cycled. You can hear it if the fuel pump is disconnected. You’ll hear a slight tick or if you have an automotive type stethoscope you can place it on the side of the injector and you’ll hear it.

City Garage · Apr 24, 2022

Gojuu said:
@City Garage that's really clear.. Thanks.

My bike sometimes doesn't start, Normally - most of the time actually - it starts really easily and then out of nowhere just won't. Cranks very well, but simply does not fire.

And it doesn't start the pump every time I hit the key. And those times are when it doesn't start (surprise, surprise.....)

I've bench tested the relay, swapped the relay with another and can see the ECU output - both in terms of using SX tune to watch the value change and with a multimeter on the terminal it signals - so was looking for the next parts of the puzzle.

Thanks again to all of you that answered. A huge help as always.

Check right at the fuel pump connection under the tank. If you are getting 12v there when switching on the ignition then you know the relay system is working. You can disconnect the fuel pump for that test and you can also apply 12v to the fuel pump side using jumpers directly from a 12v source to see how the pump runs

As long as you have confirmed 100% that each time when you switch on the key the fuel pump relay activates then you can move on to the fuel pump wiring and remember while you’re doing all this testing disconnect the fuel pump

Since the wiring is not the best on these motorcycles I suggest you check continuity for each wire on the power side the other two are for the low fuel switch. Also the wiring from the ecu to the relay.

And if when the motorcycle is running you’re not having any fuel problems then you can cross the fuel pump off the list as a fuel pump problem manifests itself rather quickly

I suspect the ecu signal is the issue.

Since you found where the prime can be changed you can increase that number of seconds to help perform some troubleshooting just remember to send it back to three when you’re done and save the program