Fuel Flow vs. Fuel Gauge

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Dave Owens

Recently my engine (1993 M25XP) failed to start, and i noticed that the fuel gauge was pegged on full with a half-full tank. Replacing fuel and both fuel filters fixed the problem, though never did figure out the false fuel gauge reading. Recently, while motoring on rough water, I noticed the fuel gauge jumping to the pegged-on-full position for several seconds, then back to normal reading, then back again repeatedly until back in the dock, at which point gauge stayed. Engine ran smoothly the whole time. I suspect this may be a warning I'm about to have a recurrance of the fuel supply problem. But what I can't figure out is: How can an interruption in fuel flow have any effect on the fuel gauge? Anybody know?
 
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Garry @ S/V TASHTEGO

Wiring

You probably have an intermitent short in the wire from the sending unit to the gage or from the 12V source to the sending unit. Probably a bare wire that is touching ground somewhere but maybe a loose connection. When you changed filters you probably moved it so that the gage worked properly and it occasionally touches ground or shakes loose when you bump around at sea. Does your gage read full when the key is off? If so that indicates that the short is in the hot (12V) side. If the gage reads empty with the power off you may have an intermitent connection to the full 12V supply either from another wire or at the back of the gage. This makes the gage go to full when it gets the full 12V without resistance instead of the reduced signal (current)from the fuel gage. Your best bet is probably to replace the gage wiring and renew the connections. Good luck.
 
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Joe Luciano

Sending Unit

I think that your problem is likely in the sending unit. I have the same issue with my C-30 right now. Check the archives. If the problem is a fluctuation in the gauge reading while the fuel is sloshing around, the sending unit can wear to a point where it won't read in certain positions. If your wire connections check out OK, this is the likely culprit. I'm going to replace mine, but haven't yet researched where to I can get it.
 
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