Fuel gauge issues

[Ratters]

Hi all,

First post... had my 2900se for a few years now and starting to better understand her.

I am not sure if this is a fault or just design issue, but my fuel gauge is giving me drastically variant information which is making it hard to rely on.

Always had the issue eg fill the tank to overflowing and then 15 minutes later having 1/2 tank displayed. But yesterday I started the boat on the dock and was told we have 5% fuel. After freaking out we decided to go for a drive. After running for about 15mins at 5kn the fuel gauge crept up over 30% and after 30 minutes with higher speeds it was saying 50%. We drove for another 30 minutes and ended the day with 40%+.

Is it fuel movement? A maintenance issue or something else?

[jparsons121]

You will get some fluctuation from fuel movement, but not like you’re experiencing.
Fuel gauges on boats are notoriously inaccurate, but should give you an approximation of the fuel level. Yours sounds like it’s needing maintenance as it’s off by way too much.
It could be a wiring issue like bad grounds or a sender that may have dead spots or a gauge that is sticky (Faria gauges are notorious for this).

Testing the gauge is fairly straightforward.
Turn key on, note the level shown.. Rap the face of the gauge with your knuckles and see if the reading changes. If so, gauge is sticking.
If no change, then you can move on to the actual testing part.
Verify you have 12V at the + terminal.
Disconnect The S wire (signal from the sender). Gauge should read Full.
Jumper the S terminal to the - (ground). Gauge should read E.
If all these pass, then gauge is good.

Checking the sender requires a meter in the Ohms setting.
Initially, you can test with the sender still installed. Probe between the signal terminal and
Ground. Reading should be between 33-240ohms for US senders. 33 being full and 240 empty. You can roughly guesstimate what the reading should be if you know the fuel level in the tank. Readings are pretty linear. Ie 100 ohms is approx 1/2 tank.

Checking the sender out thru the entire range involves removing it from the tank and moving the arm or the float thru the entire range observing the Ohm readings.

If both check out, then it’s a connection/wiring issue. Next check all of the connections at both the dash and at the sender/tank, particularly looking for and ground issues.

[Ratters]

Thanks for the comprehensive answer.

The results are the same on the needle and the digital % on the speedos, so I assume it's not the gauge but one of the other items.

I'll work through them and hopefully get the culprit.

[jparsons121]

Go for the easy part first then. Check the wiring and be sure the sender has a good ground and the signal wires connections are solid. I’ve used an ohm meter with a long jumper wire to see if the grounds are good between the tank and the dash grounds. Dirty connections will add resistance and fake the gauge into thinking there is less fuel than there really is.

If that checks out, then it’s the sender. It may just be gunked up and the sloshing of the fuel helps it free up and the float actually floats. Pain in the ***** to trace, but overall a pretty simple design.