How to diagnose fuel gauge problem

[Joe500]

My boat has been on land for two years. I came to test it out prior to putting it in the water. To my surprise, the Volvo Penta 2003 diesel engine started easily. However, the fuel gauge didn't move, and remains far below zero (see photos). I suspect the problem is more likely to be a corroded electrical connection between fuel sender and instrument panel, rather than a problem in the fuel sender or instrument panel itself but I'm not sure how to test these items. Can I use my voltage multimeter to check? What exactly should I measure? Thanks, Joe

[Wotname]

You could measure the resistance of the sender. The resistance will vary according the amount of fuel in the tank. The two common industry standards are 10 to 190 ohms and 240 to 30 ohms. I can't identify which one you have but either can tested by shorting the terminals at the sender (i.e. zero ohms) and then disconnecting one of the terminals (open circuit). The gauge should either got from full to empty or vice versa.

On the back of the gauge there will be (usually), 3 wires. 12V +ve, Gnd (12V -ve) and a wire from the sender. Use the voltmeter to check there is 12V+ve and the Gnd (12V -ve) at the gauge terminals. If so, then connect the sender wire to gnd. It should give you a full or empty reading and vice versa if the sender wire is disconnected.

[OldGreyB]

See this previous thread for more information:

https://www.cruisersforum.com/forums...pe-203806.html

[GordMay]

See also:
Basic Engine Gauge Theory and Testing ➥ https://www.cruisersforum.com/forums....html#post2597

If a Sender [float] fails “Closed” (shorted - Zero Resistance), the Gauge will read Full Scale [full].

The resistance, from float to ground, should measure:
American Floats: 240 Ohms (Empty), 103 Ohms (½ Full), & 33 Ohms (Full)
European Floats: 10 Ohms (Empty), 95 Ohms (Half), & 180 Ohms (Full)
Automotive & other Float Switches may use other resistances such as 0 - 90 Ohm, 73 - 10 Ohm, & etc.

[Rumrace]

Fuel gauge is an omhs meter. They ground out inside eventually. It can probable be rebuilt.

[Rumrace]

https://www.bobsspeedometer.com/

There is a guy who just does Smith. He’s really good but just Smith.
I have a 1953 Triumph and a 1952 Harley. The gauges are all original restored. The Triumph has a Smith estimates speed by rpm and gear. Has electric charging fuel also in one gauge. Fuel gauge is new diode contacts card paint glass seal and back in the post to you. Or pick up a newguage on line from Princess Auto

[Joe500]

Great, thank you all for the prompt advice. I will try what you suggest.

[tkeithlu]

QUOTE: "Fuel gauge is an omhs meter"

Well, sort of. The sensor is a variable resistor, and the fuel gauge measures the voltage given the drop through the resistor. Ohm meters apply their own small voltage and again measure the voltage drop.

[sinnerman]

My bet is on corrosion at the wire connections at the gauge or in the wiring harness, especially if there are any "quick disconnect" connectors installed.

ABYC color code for the fuel gauge wire is "pink" color..

My two cents.

Cheers

[Boatyarddog]

Originally Posted by Joe500

My boat has been on land for two years. I came to test it out prior to putting it in the water. To my surprise, the Volvo Penta 2003 diesel engine started easily. However, the fuel gauge didn't move, and remains far below zero (see photos). I suspect the problem is more likely to be a corroded electrical connection between fuel sender and instrument panel, rather than a problem in the fuel sender or instrument panel itself but I'm not sure how to test these items. Can I use my voltage multimeter to check? What exactly should I measure? Thanks, Joe

You'll need a DMM or test light, for some tests mentioned here
With key switch on, the gauge needle will come up to the 0 mark if it has power at the gauge, and a good ground.
Jump the sender leads together at the tank, if the gauge jumps up, it's a sender problem.
And you can replace it.

If it does not, check the voltage of the + lead to ground at the gauge, it should be battery voltage, check fuse, iand you have power at the + lead.

Be sure your sender wire has continuity, use a multimeter for this.
One lead of the DMM on the sender lead, at the tank, the other DMM lead on the gauge sender lead, usually brown, or grey.



Be sure your ground lead at the gauge is solid, has good connection to the battery, as well the tank ground.

Now at this point you've tried the quick tests.

Now all these other tests may isolate the culprit.
But your not going to repair the gauge, cause you can't get parts for it.
Unless it's a classic or you got to keep it, replace it.
There not user serviceable units.
Go Stewart Warner gauges, Quality guages.
Quality, or Faria cheap alternative.

You'll have to remove the fuel sender to test it too,
At that point just do yourself a favor and replace it.
Senders are cheep too.

In most cases it's the sender, a lack of power or grounds, or broken wires.
But can be a lack of power, to the gauge.

I'd not worry about, values and ohms, just connections for integrity, and voltages, and continuity
You can just check for continuity between their connections.
Boatyarddog