If your fuel pump fails, you're in an isolated area and you don't have a spare, simply connect a wire from the yellow - grey wire (earth to injectors) to the battery negative post,  and you can ride home. 

This provides constantly open injectors, which with the help of gravity fed fuel and vacuum from the pistons, is enough,  but not ideal,  to ride home. It is sometimes a little on the rich side which can be overcome by backing off the throttle. 

I have proved this today with a one and a half hour ride (45 minutes each way)  reaching speeds of 100 kmh (60 mph)

This was with a 2v brick. The pump is working, so I simulated a failed pump by disconnecting the fuel pump electrical plug.

It helps to keep the revs high.

If the pump were to suddenly start working again, that would result in a stall because of the constantly open injectors, so unplugging the fuel pump plug would be best with this temporary modification.

amazing ...!!!!

daveyson wrote:If your fuel pump fails, you're in an isolated area and you don't have a spare, simply connect a wire from the yellow - grey wire (earth to injectors) to the battery negative post,  and you can ride home. 

This provides constantly open injectors, which with the help of gravity fed fuel and vacuum from the pistons, is enough,  but not ideal,  to ride home. It is sometimes a little on the rich side which can be overcome by backing off the throttle. 

I have proved this today with a one and a half hour ride (45 minutes each way)  reaching speeds of 100 kmh (60 mph)

This was with a 2v brick. The pump is working, so I simulated a failed pump by disconnecting the fuel pump electrical plug.

It helps to keep the revs high.

I partially pulled back the rubber gaiter between the fuel injector unit plug and the wiring harness to gain easy access to the yellow /grey wire. If the pump were to suddenly start working again, that would result in a stall because of the constantly open injectors, so unplugging the fuel pump plug would be best with this temporary modification.

It can also cause the coils to overheat in the injectors which will cause you lots more grief and a new set of injectors.

Good to know,  thanks,  I never thought about that. So I spose only worth the risk if you're really desperate. Are there other pitfalls with this modification?

Anyway, at least I have found out it's possible to survive a 45 minute ride.

I was actually wondering about the fuel temperature as there is no pump circulation for the fuel.

If it had been summer and 40°C you would have fried the injectors. they only open for a matter of micro seconds and so don't get hot normally

Beauty.  Thanks for your help with understanding this strange situation.

Great tip !!

Well we see 45 but its those Fn degrees so its a good tip to know.

That should go up in a place along with Sidecar Pauls tip on non opening fuel caps and a few more things.

A cheap AliExpress OEM copy pump is cheap insurance, I have one fitted to the bike and a new spare in the tail.
Regards Martin.

MartinW wrote:A cheap AliExpress OEM copy pump is cheap insurance, I have one fitted to the bike and a new spare in the tail.
Regards Martin.

Hi Martin,
Do you have a link for that please?
Thanks, Stu

Stu go to this link https://www.aliexpress.com/ And type in BMW K100 fuel pump and you'll get multiple sites. I've been running one with no problems since July 2017. http://www.motobrick.com/index.php/topic,10054.msg86054.html#msg86054 It ran faultlessly on a 3 day 1400 Km trip in 40C + heat.
Regards Martin.

MartinW wrote:Stu go to this link https://www.aliexpress.com/ And type in BMW K100 fuel pump and you'll get multiple sites. I've been running one with no problems since July 2017. http://www.motobrick.com/index.php/topic,10054.msg86054.html#msg86054 It ran faultlessly on a 3 day 1400 Km trip in 40C + heat.
Regards Martin.

Cheers Martin

I still get a chuckle now,  thinking back on that day.  

That ride was to a mates place ( rides a kle500,  cheaper rego) This was one tall story that simply went too far to believe. He thought a fuel injected motorbike,  or a fuel injected anything, couldn't run with the fuel pump unplugged, and wouldn't believe it unless he saw it with his own eyes. He looked at the wiring, he followed the fuel lines from go to woe,  looking for a hidden pump... eventually... eventually... reluctantly... he conceded. The look on his face was priceless, he was shocked to the shit house. 

I, myself, felt like a stunned mullet, when I finally got this non running bike going by unplugging the fuel pump! I even hopped on it and rode around the block, as I was riding, I remember thinking "this is bull shit,  but it's true" I couldn't get the smirk off my face.

Somehow I fixed the problem, without ever finding the cause. A year or so later, I tried to reproduce the problem. With a bit of effort and help,  I found this way. 

The bike runs a bit rich like this, but feels pretty normal if the revs are kept high.  It's down on power though,  so the revs might drop if you're going up a steep hill,  so then you have to down change well in advance, to keep the revs high,  a bit like driving a truck. 

OK, now for the "over my head" bit. 

The book says bricks run on a fuel pressure of 36psi. Atmospheric pressure is 14.7psi. Engine vacuum of 20 inches of mercury, let's say that converts to 10psi. (don't know if this applies to bricks,  or bikes) So let's say 25psi, that's enough. Especially considering the injectors are constantly open instead of momentarily, which makes it more than enough.

Here's a photo of the mighty beast that inspired this journey.
I took it for a spin today. 
Because of its unregoness,
You hardly ever see the mighty beast down here
He only come to town about twice a year.