Any way to "dummy out" fuel sensor on R25 Cummins?

[NorthernFocus]

The fuel sensor is failing on my R25 w/Cummins 150hp. I don't care about the lack of tank level indication because it has never been accurate anyway. But now it has started drifting up and down (seemingly at random) and goes in and out of critical alarm. As far as I can determine there is no way to program out the low fuel level alarm. And I don't want to go through the hassle of cutting the deck to access the sensor. The alarm is very annoying sometimes activating/clearing every few seconds. But worse it can cause one to ignore real alarms if they occur. Is there a simple way to defeat/bypass/aka dummy out the fuel sensor so that the computer simply thinks the tank is always full?

 

[knotflying]

Just taking a guess here, but the sensor works with resistance. I am not sure if it shows full with more resistance or less. However, can you find the leads coming off the tank and cut them? If full is more resistance than taping them off should do it. If no resistance reads full than joining them together should correct the problem. Just a thought.

 

[Andrew Custis]

You should be able to disconnect the wiring which would eliminate this. Usually it is a pink wire leading to the sender. You should be able to see it from the mid cabin by removing the panels that are on the inboard starboard lower edge. Remove those 2-3" tall carpeted panels and that should gain you access.

Thank you,

 

[NorthernFocus]

Thanks for the input, Mike. I also assume it's a resistance device. Finding the wires is the trick. Which Andrew provided some clues to.

Thanks for the feedback, Andrew. Hopefully tomorrow I'll be aboard and take a shot at finding said pink wire. Will provide feedback on how it goes.

 

[NorthernFocus]

Update on this topic for future benefit of any Cummins owners who run across this problem.

I finally got around to dealing with this and it was a bad news/good news story.

Bad news, the Mercruiser control system is too smart for our own good. It won't let you make the simple fix of opening or shorting the circuit. Doing so causes a high/low input signal error which defaults to a critical low fuel condition. The book says that the critical low fuel alarm limits the engine speed. Luckily (for once) the documentation doesn't match the actual functionality. It does not limit engine function. It's just annoying having the alarm change state every time you hit any significant waves/wakes.

Good news, I found a "button whip" solution. In the manual there is a procedure for calibrating the fuel tank sensor. The first steps in the procedure are to set up the tank. One of the variable you have to define is fuel type. The choices are gas, diesel, water, or "no used". You see where this is going? I simply changed the type to "not used", reconnected the wires to the sensor and voila. The system freaks out if you don't have enough fuel but is fine with having no fuel tank. Problem solved. Great thing about it is that if it happens to you while you're on the water you can take care of it.

Just an FYI...