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  Sending unit or fuel gauge problem?

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Author Topic:   Sending unit or fuel gauge problem?
Eagleman posted 11-11-2001 09:54 PM ET (US)   Profile for Eagleman   Send Email to Eagleman  
1984 22' Outrage w/70 gallon built tank with Tempo fuel gauge on the console. I have 12 volts at the built in fuel gauge on console but the fuel gauge indicates empty with 70 gallons of fresh fuel on board. What type of test can I run to determine if it's a bad sending unit in the tank or a bad fuel gauge? Thanks
jimh posted 11-12-2001 09:14 AM ET (US)     Profile for jimh  Send Email to jimh     
There is a related thread on this topic:
http://continuouswave.com/ubb/Forum3/HTML/001325.html

The gauge responds to current that is controlled by the resistance of the sender. Generally a reading of "E" corresponds to the minimum current flow, perhaps in this case no current flow.


There are two possible domains in which the failure has occurred: Mechanical or Electrical:

Mechanical: The float mechanism is stuck or damaged or in some way no longer mechanical connected to the sending unit.

Electrical: The circuit is open.

The circuit is typically:

Battery Positive --> Switch (part of ignition switch) --> Meter Positive --> Meter Negative --> Wire to sender --> Sender Variable Resistance --> Metal of Tank -->Tank Ground Wire -->Battery Negative.

I hesitate to proceed further in detailed trouble shooting steps, as this is pretty basic, ELECTRICITY 101 stuff. If you know enough to diagnose and repair it at this point you won't need more help. If you don't know enough to diagnose and repair it, there is probably nothing I could tell you in the limits of this communications medium that could explain it to you.

--jimh

jimh posted 11-12-2001 09:17 AM ET (US)     Profile for jimh  Send Email to jimh     
Two quick tests:

Measure the voltage present at the meter and the sender with reference to the Battery Negative.

bigz posted 11-12-2001 09:52 AM ET (US)     Profile for bigz    
After you determine you have 12v at gauge and sending unit and that is ok.

Easy to tell if gauge is working ground the sending wire on the tank -- if gauge moves to full then it's the sending unit.

May be as simple as a saturated float! It can/does happen in older boats.

When and if you remove the sending unit might suggest picking and installing a new gasket -- that is off course you don't purchase a new sending unit and float it will be included.


whaleryo posted 11-13-2001 03:54 PM ET (US)     Profile for whaleryo  Send Email to whaleryo     
I had a similar problem that went away when I removed the grounding wire, cleaned all surfaces, sprayed with WD-40 and reconnected. It costs nothing to try this, and should probably be done anyway.
jimh posted 11-14-2001 08:00 AM ET (US)     Profile for jimh  Send Email to jimh     
whaleryo--I am curious about your wiring of the electric gauge. Can you recall a few details?

Usually there is a large (10 AWG) conductor with green insulation that runs from the fuel tank to the bronze electrode on the transom. Is this the wire whose connection you restored?

Was there another wire running to the gauge sender from the battery negative?

whaleryo posted 11-16-2001 11:21 AM ET (US)     Profile for whaleryo  Send Email to whaleryo     
Jim,

I didn't see any ground going to the transom from the tank. There is a ground from the battery connected to a lug on the fuel tank. A wire goes from the sending unit to the gauge, and another one from the tank grounding lug to the ground on the gauge. I cleaned both the sending unit connection and the grounding lug connection.

Hope this helps,

Bill

jimh posted 11-16-2001 01:39 PM ET (US)     Profile for jimh  Send Email to jimh     
The typical fuel system on a Whaler with internal tanks has all the metal elements of the fuel system bonded together with a 10AWG insulated wire (green). This grounding conductor leads aft, traverses the transom, and leads down the outside of the transom to a sintered bronze fitting about the diameter of a silver dollar that is afixed to the transom below the waterline.

Such bonding and ground conductor are needed to maintain the metalic parts of the fuel system at a uniform potential and as close to "ground" (or in this case "water") as possible.

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