Yamaha Fuel Gauge Diagnosis

Electrical and electronic topics for small boats
Will
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Yamaha Fuel Gauge Diagnosis

Postby Will » Mon Dec 30, 2019 10:35 am

[This topic is moved to SMALL BOAT ELECTRICAL for discussion--jimh]

I have a 2010 Yamaha F150, 2010 Yamaha gauges, and a 2010 Florida Marine Tank in my 1991 Boston Whaler Outrage 19.

The fuel gauge is flashing one bar. I disconnected the sending unit wires yesterday and I am still getting one flashing bar.

Is this a loose wire between the sending unit and the dash?

Or, do I need a new sending unit?

Thank You - Will

jimh
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Re: Yamaha Fuel Gauge Diagnosis

Postby jimh » Mon Dec 30, 2019 10:54 am

Will wrote:The fuel gauge is flashing one bar.


My inference is that a display of one flashing bar is abnormal. Consult the owner's manual of the Yamaha fuel gauge to determine what the indication of one flashing bar means, and provide that information in a follow up. It is not clear to me if the essential deviation from normal is the flashing condition or the one-bar condition. Provide further information about this.

Will wrote:I disconnected the sending unit wires yesterday and I am still getting one flashing bar.


Your test does not provide any basis to draw a conclusion about the location of the fault.

More information needed

What is the actual tank level as determined by some other basis than the Yamaha tank level gauge? This information is necessary in order to have a basis to infer a proper resistance reading in the sender.

Suggested Test Procedure

I suggest you temporarily disconnect the circuit between the gauge and the sending unit at the tank end of the wiring. Then measure the resistance of the sending unit right at the fuel tank.

The expected resistance of a tank level sending unit made for use in the USA is likely to be between 33-Ohm (at full tank) and 240-Ohm (at empty tank). (A separate article has more information about tank level sender resistance.) Based on an inference about the actual tank level, compare the resistance reading to the inferred actual tank level to see if they are congruent.

If the tank level sender resistance is not in the proper range, then the fault is likely in the tank level sender.

If the tank level sender resistance is in the proper range, then reconnect the circuit from the gauge to the sender. Move to the gauge. Temporarily disconnect the circuit from the gauge. Measure the resistance in the circuit. It should be the same as you measured at the tank sender directly.

If the resistance of the circuit at the gauge end of the wiring is different than at the tank end, the problem is in the wiring between the tank and the gauge.

If the resistance of the circuit at the gauge end of the wiring is the same as at the tank end, then the fault is likely in the gauge.

Perform the above procedure and reply with your observations and readings of resistance.

In my estimate, the component with the highest probability of failure is the wiring between sender and gauge, including loss of one leg of the circuit. Often the negative return (or ground) side of the circuit may be missing. Or there may be corrosion in a connection.

Regarding connections, do not trust an electrical connection in low-voltage circuits (like a 12-Volt DC circuit) based only on the appearance of the connection. It is common for connections to have the appearance of mechanical integrity, but for there to be an electrical discontinuity in the connection. This is due to the formation of a very thin layer of insulating material (corrosion) in the connection. At low voltages, electrical current flow can be stopped by a very thin layer of insulating material which may not be readily seen. Sometimes a disassembly of the connection, then cleaning of the terminals with WD40 and possibly some very soft abrasion (with perhaps 600-grit cloth and wet sanding with WD40) will be necessary to restore an electrical connection.

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Phil T
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Re: Yamaha Fuel Gauge Diagnosis

Postby Phil T » Mon Dec 30, 2019 3:26 pm

A single blinking bar is the low-fuel indicator.
To troubleshoot - paraphrased from a well respected Yamaha master mech (Rodbolt):

- The pink wire is send.

- Ground the pink wire to a known good tank ground. (You may wish to check your tank grounds as well)
Once you have determined a good ground, with the key on, connect the pink wire at the sender to ground.

-Wait 20 seconds or so and the gauge should react. If not you may have a bad ground or connection between the pink wire and the gauge white wire. Note the color changes at the meter. if it reacts you most likely have a bad sender.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

jimh
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Re: Yamaha Fuel Gauge Diagnosis

Postby jimh » Mon Dec 30, 2019 4:54 pm

PHIL--if the gauge indicated low tank level, then the sender resistance should be close to the 240-Ohms expected.

The procedure to test you paraphrase seems like it follows the procedure I suggested with actual resistance measurements. I find that often test procedures for mechanics trying to diagnose electrical problems are given in rather odd ways where the person testing has no knowledge of electrical behavior. I think these procedures result from an assumption that electrical problems are out of the realm of knowledge of the usual outboard engine mechanic or outboard engine owner.

The circuit in this case is trivial:

GAUGE---> WIRE ---> VARIABLE RESISTOR

The procedure I described allows assessment of all three components of the circuit with simple resistance measurements. Being able to measure the resistance of a circuit element in an electrical circuit is a basic skill necessary for diagnosis of problems in electrical circuits. If resistance measurement is not within the skill of the person trying to assess an electrical circuit, then it is probably time to seek some outside help--but perhaps not from a mechanic.

In the typical tank level sensor, a high resistance means a low or empty tank. We don't know if the gauge display is indicating a warning of a low or empty tank because the sender resistance is close to 240-Ohms or because the sender has become disconnected and the gauge sees an infinitely high resistance from the sender. Measuring the actual resistance will be useful to understand what component is the actual cause of the problem.