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Old 10-25-2004, 05:21 PM   #8
Poolside's Avatar
Joined: Apr 2003
Location: Long Beach, CA
Oddometer: 11,887
Thanks for the great pictures Dutch. If the fuel pump controller was replaced, your bike should be in good shape.

That aluminum-finned device, though not part of the CANbus, is a controller. It is a controller/driver for the fuel pump. The controller initially operates the fuel pump at 100%, and then switches to an 80% duty cycle.

This new fuel pump controller on the 1200 is inserted into the bike's wiring EXACTLY where the fuel pump relay is on the 1100/1150 models. It is not part of the CANbus.

These new 80% duty cycle controllers were replaced at a high rate on the early chassis numbers. The first edition controllers are not designed very well. They overheat and die. But before they stop working, the excess heat warps the plastic portion of the case. The warped case ruins the shape of the o-ring groove causing it to leak.

Liquid isn't the issue here, it is the controllers themselves. Water is a poor conductor of low voltages. The the external electrical connections to the fuel pump on the 1100/1150 are unsealed. The alternators on both bikes are unsealed. Most every connector on most every motorcycle ever built is unsealed.

As an aside, there is an oblique benefit to mounting the controller outside of the fuel tank. It can be bypassed if you are stuck in the middle of BFE. Bypassing the controller lets the fuel pump run at 100% while you get home, but that is not an issue.

(the same 'bypassing' can be done with the 1100/1150 if the fuel pump relay fails)

According to BMW, the reduced duty cycle provides two things. One, it uses less current. And two, since the fuel system is a recirculating-type, operating the fuel pump at 80% circulates the fuel through the fuel filter less often. BMW claims the reduced fuel recirculation rate means the fuel filter does not require periodic maintenance. BMW claims it's a 'lifetime' filter.

- Jim


Some advances in fuel systems -

With current and recent designs, fuel circulates back to the tank after having been shunted at the fuel pressure regulator. The pump runs all the time, and fuel makes continuous round trips to and from the tank.

The newest automotive fuel systems are not the recirculating type. These new systems are similar to the 'dead end style' 'carburetor and mechanical fuel pump' systems of years ago. Similar to the older systems where the fuel was on a 'one way street' from the pump to the carburetor, these latest systems transport fuel only from the tank to the injectors. The fuel does not make a return trip to the tank.

The new systems do not recirculate fuel, and do not use a mechanical pressure regulator. Instead they use a sophisticated fuel pump controller and a brushless DC motor in the pump. The speed and timing of the brushless motor in the fuel pump is electronically controlled to maintain the system fuel pressure over all operating conditions, from idle to full-throttle.


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Poolside screwed with this post 04-15-2009 at 07:23 PM
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