Fuel pump start/shutoff

[MEZ]

Hi all, just need to clarify my thoughts with some back up from any boffins on here, basically I have built an out of tank fuel system which pressurizes the rail fine but I just cant get my head around how the pump is supposed to function. I've just read a post that states the pump is initiated as the start button is depressed and stays on until the engine is killed. Any info much appreciated....

[kennybobby]

The electrical circuits that control the fuel pump provide for operation while starting, during normal running, and then a safety cut-off feature in the event that the engine stalls or quits running.

The pump has an internal safety vent if the output pressure exceeds about 70 psi.  The fuel pressure regulator is set to provide a rail pressure of about 36 psi above the intake manifold pressure, and it recirculates the excess fuel back to the tank.  There is a fabric screen filter on the pump intake and a full-flow filter on the output side.

Are you building an external fuel system for testing or to run all the time?

[Scott_]

Also, the fuel system control is slightly different depending on what year/model bike you are working on.

Sent from my SCH-R970 using Tapatalk

[MEZ]

Hi Kenny, I am building a K75 Adventure bike with a bespoke tank hence the 'out of tank' pump/fuel system. I'm beginning to understand why I have been confused slightly here, I have been looking for voltages while testing when the bike is not running. I'm guessing that the fuel injection relay is energised when cranking for a start then stays energised while running giving a feed via the green/red wire through a fuse that then becomes the green/white wire to the fuel guage which in turn gives the pump its feed. I have used this green/white wire to trigger a relay which then feeds the pump. I have the rail set at 36psi controlled with a 1:1 ratio pressure regulator and return feed to tank. It all works fine but I had the mentioned relay on a frig wire permanently running it while testing. We have made a new fuel rail from stainless steel because the old mild steel one became porous when we welded on two dash 6 fittings, a lesson learned as it set light from a blow back and we had FIRE...!!!
If your interested you can check out the bike on my website here : www.olscomponents.com

Thanks for your input and interest guys, this site never fails to impress with the depth of knowledge from 'K' followers....!! 

[Scott_]

There should already be a relay in the electrical box under the tank. The stock relay is driven by the fuel control system.
A relay to drive a relay, seems a tad overkill, and another point for trouble shooting failure(hair pulling out situation.... lol)
You mention you are working on a K75, so that should be a Jetronic fuel controller. This system will energize the fuel system when the starter button is depressed, and then it is continued to be energized by the input from the hall sensors sensing engine rotation.

[kennybobby]

i suppose you are still using the OEM fuse panel and electric box that holds the relays. 

On the k75 there are three 15A fuse circuits #3,4,5 (counting #1 at top, 7 at bottom) that have direct +12 battery voltage (hot all the time) coming into the right blade toward the rear of the bike, the forward or left blades run to the loads.  #4 is not used and is available as a spare.  The load circuit wires are either red/white or red/yellow.

One of the fuses #2, gets voltage when the key switch is turned to the first position (park).

Fuse #7 gets voltage thru the Load Shed Relay when the key switch is turned to the second position (ON) regardless of the position of the Kill switch.  The load circuits are green/brown wires.  The LSR is always energized except when starting.

Fuse #1 only gets voltage when the key switch is ON and the kill switch is in Run position.  The hot side (switched, but unfused, direct battery voltage) are green/yellow wires and the fused load circuits are green/black wires.  This circuit provides voltage to the Start Button, and the starting circuits energized after the button is pressed are the yellow/black wires which run to the Start Relay and pin 4 of the L-Jetronic Unit for starting enrichment.

The Ignition Control Unit also gets powered up at pin 10 by the unfused green/yellow.

Fuse #6 only gets voltage when the Fuel Injection Relay is energized, which requires key ON, Run position, And either the Start is pressed Or the engine is actually running.  The input wire is green/red, and the fused load circuit wires are green/white.

When the starter is cranking and the engine is turning over, or when the engine is running, the Hall Sensors provide a timing pulse signal to the ICU which then controls the FIR by the yellow/brown wire from pin 7.  The ICU pin 8 also sends a timing pulse to the Jetronic unit pin 1 on a yellow/red wire.

Obviously any of the unfused power wires will make lots of sparks and melting if shorted to ground and need to be carefully handled and checked.

Interesting build you have going, need to see more about this extra fuel tank...

[MEZ]

Hi Kenny / Scott,  thanks very good info here, this has confirmed what I was thinking but didn't know the absolute ins & outs of how it actually worked, now I do...!!!! I will check that the hall sensors connector is plugged in 100%, this must be the wire heading down the front of the engine yeah..??

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[Scott_]

I will check that the hall sensors connector is plugged in 100%, this must be the wire heading down the front of the engine yeah..??

Yea, they head down the front of the engine, to the sensors behind the "T" shaped cover.

[MEZ]

There should already be a relay in the electrical box under the tank. The stock relay is driven by the fuel control system.
A relay to drive a relay, seems a tad overkill, and another point for trouble shooting failure(hair pulling out situation.... lol)

Hi Scott, the reason for the relay is to drive the Walbro pump which runs at a higher FLC and would probably blow the fuse which feeds the fuel injection relay and its a 30amp rated so less stress on the contacts. I sourced a job lot of Audi relays of fleabay and anything from the 4 wheeled automotive industry is going to be very robust in build quality I would of thought...!!! Scott or Kenny, do you know anything about the high altitude 'jumper' plug/connector and if a simple switch between the concerned wires would do the job..???

[kennybobby]

No fuse feeds the Fuel Injection Relay--it has a direct connection to the battery +12V.

The altitude plug is just a jumper.

[MEZ]

No fuse feeds the Fuel Injection Relay--it has a direct connection to the battery +12V.

Hi, yeah sorry, the fuse post FIR that feeds the fuel guage I meant...!!!

[MEZ]

She's a running...!!!  Must of been the fuel injection harness that caught alight. New harness £15 ,new plugs and she is purring like a pussycat. Small test ride now to check general feel of new seat hight, pegs position and the all important front end weight distribution that so many people are concerned about...!!!!! I'm starting to love these 'K' engines....

[beemrdon]

Wow! That K bike is insane...got any more pics MEZ?   :riding:

[MEZ]

Wow! That K bike is insane...got any more pics MEZ?   :riding:

Hello Mate, I'm steering folk through my website where there is the article from ABR magazine and some pics... have a gander.. www.olscomponents.com

Cheers Mez

[Filmcamera]

That link doesn't seem to work for me...

[beemrdon]

I only saw 1 pic of a final drive.

[Laitch]

That link doesn't seem to work for me...

I only saw 1 pic of a final drive.

There's a whole lot here.

[MEZ]

There's a whole lot here.

that link takes me straight to the site...!!!!!!?????!!!!

[Laitch]

that link takes me straight to the site...!!!!!!?????!!!!

To your Project thread on the site, to be specific, MEZ. beemerdon was looking for more pictures, and there are plenty there. The link to OLS site still works for me.