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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: ccalverto on November 16, 2017, 11:07:22 PM

Title: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: ccalverto on November 16, 2017, 11:07:22 PM

Hey - Ive changed the whole inside of the tank out on my 1991 K100 RS 4V but when i turn on the ignition the fuel pump keeps going recycling in the tank.


I've taken a video here: [size=78%]https://youtu.be/AEN1bX439Fg (https://youtu.be/AEN1bX439Fg)[/size]


The fuel pipe to the injector rail us under pressure i just cant explain why it is coming from the top of the tank roof.


Anyone help?

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: The Mighty Gryphon on November 16, 2017, 11:46:25 PM

That is the return from the fuel pressure regulator you see in the tank.

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: ccalverto on November 16, 2017, 11:55:43 PM

Why would it be doing that?

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: Martin on November 17, 2017, 12:27:52 AM

The fuel pump is on continuously with the Bricks. It does not stop start like some the FPR returns unused fuel back to the tank.
Regards Martin.

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: ccalverto on November 17, 2017, 01:05:45 AM

dammit - i was hoping that was the reason it wasn't firing over!!! - thanks all for your help.

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: Laitch on November 17, 2017, 01:09:02 AM

I think you need to study how your bike works. Hope doesn't cut it. :giggles

Several good resources in the Repair Guidance section's master list.

Title: Re: Fuel pump doesn't stop after prime and overflows back into tank from the top
Post by: Scott_ on November 17, 2017, 06:48:40 AM

Have you measured the pressurized line(injector rail inlet) with a gauge, it's possible your FPR is failing and bypassing too much fuel back to the tank, thus not having enough "push pressure" to get the correct amount of fuel thru the injectors when they open.

The fuel pump should not run continuous without the engine turning.
Older Jetronic control systems power the fuel pump when the start button was pressed, and then the pump continues when the controller detects engine rotation signal from the HES sensors.

Newer Motronic systems "prime" for about 3-5 seconds when key is turned on, then pump turns off until engine rotation is detected by the HES sensors.