Fuel gauge quit working

[crashpro]

I have a 1987 Astroglass bass boat that the fuel gauge quit working. It has a 22 gallon built in tank. It worked fine at the end of last season, worked intermittently Feb. and March, and now has quit working all together. We found online how to check the gauge and the sending unit. Both tested good. We then checked the wiring and there was continuity (no broken wires). We also cleaned all of the terminals. We even ran new wires directly between the gauge and sending unit and it still didn't work. Gauge has 12.95 volts coming into it and we read 7.94 volts between the ground and pink wire with a 7/8 full tank, both at the gauge and sending unit. Removing the pink wire from its terminal on the gauge, the terminal reads 10.45 volts to ground. Individually, all components check as they should, but as a system, the gauge always reads "E."

 

[Silvertip]

Re: Fuel gauge quit working

While you may have 12 volts on the gauge, you may NOT have a good ground. While the pink wire may show continuity between the sender and the gauge, the sender mounting flange may not be grounded either. Even if all of the connections are fine, the thing you are missing is a "resistance" check of the sender. If you have a full tank (or close to it) disconnecting the pink wire from the sender and measureing from the sender post to the flange should show about 33 ohms. 1/2 tank about 109 ohms, empty tank about 240 ohms. Those readings can obviously vary a bit but if you get no reading or a reading very different than listed, you need a new sender. Did you "momentarily" short the "S" terminal on the gauge to ground to see if the needle pegged full? If it doesn't you 1) do NOT have 12 volts on the gauge, 2) do NOT have a good ground on the gauge, or 3) you DO have a bad gauge. I highly doubt #3 is the issue.

 

[crashpro]

Re: Fuel gauge quit working

We did the "momentary short test" on the gauge terminals and it performed flawlessly. I am thinking the problem has to be at the sending unit area. I will check the things you mentioned at the sending unit and we will remove it from the tank today. It is very difficult to get to, which is why I have procrastinated in pulling it out. Tank is nearly full and sending unit measured 38 ohms.

 

[Silvertip]

Re: Fuel gauge quit working

You can make a resistance measurement using the pink (send) wire at the gauge. Disconnect it and measure resistance from the pink wire to a KNOWN GOOD GROUND. Depending on how much fuel is in the tank you should read the number I listed earlier. While that can only test one aspect, it can prove the wire is good. You need to remove the sender to check resistance across its entire range of motion.

 

[crashpro]

Re: Fuel gauge quit working

I did what Silvertip recommended to check the sending unit through its entire range of motion and found it was defective. Installed a new one and am back in business. Thanks everyone!