fuel gauge problem

[yellowcat12]

Not sure I'm in right place but I have problem with fuel gauge. When I turn ignition switch the gauge reads pretty much correct. When I start the engine the gauge slowly starts to rise and continues to rise to full and remains on full until engine is shut off. The tank is approximately 1/4 full. I have looked at many sights but none of them deal with this problem. Thoughts?

 

[gm280]

First things first yellocat12, :welcome: to iboats. Nice to have you join us...

With the little bit of info, it sounds like an electrical issue for sure. If you have a multi-meter and know how to use it, take some measurements with the ignition on and then with the engine running. If there are any differences, you found your problem and you need to locate where the difference is coming from. You can check the voltage either at the fuel gauge itself or at the fuel sender at the tank. I would start by verifying you have clean and solid ground wire connections. So many problems are the result of corroded ground wires and connections. JMHO!

 

[Grub54891]

I'd say the gauge itself is ok. Testing it just requires removing the wire from the sender and grounding it to the tank, if it goes to full, its good. if not its bad. Now remove the sender, and hook up an ohm meter, slowly raise the float, and watch the values to see if they are jumping or losing readings anywhere in its range. Not sure of the ohm readings you would get, as some are different than others. It's possible you have a backfeed issue that makes it do that when its running, I guess one place to check is at the alternator, set your meter to ac volts, and start it up. Yes the dc side will show ac volts, just not more than 0.4 ac volts leakage past the diodes. That will show you if the alternator is weak, or going away giving ya goofy symptoms. Most issues are simply bad grounds somewhere in the boat, causing current to look for a place to come from or look for ground. Clean shiny grounds are important!

 

[StarTed]

The above suggestions are good.

I've seen something like this happen on a Ford van when the voltage regulator for the gauges didn't work properly.

As GM stated, check the voltage on the high side of the gauge and monitor it through the problem when the engine runs. I'll bet the voltage rises making the gauge move up since it sees the difference between the gauge supply and the sender side. The voltage on the sender should remain about the same. If it rises, you probably have a connection problem with either side of the gauge.

Grounding is very important for the sender. Its function is to vary the current flow through the gauge by controlling the resistance on the ground side of the gauge. So, you may also have a ground connection problem.

 

[tpenfield]

Just a thought . . . since the gauge reads properly with the ignition key on, but not when the engine is running, I would check to see if there is a short (or improperly connected wire) of the fuel gauge or sender wiring to the alternator wiring.

Googling a wiring diagram for your engine should help as well . . .

Electrical stuff is hard to chase, but hopefully with a multimeter and a wiring diagram, you will find the problem.