fuel tank ohms changing - Lateral-g Forums

awesometool · #1 07-13-2010, 02:16 PM

The fuel Gauge changes when going from accessory to the engine running. I tested the ohms directly from the tank full and empty and it was 0-91 ohms. perfect. I drained the tank and the gauge also went from full to empty following the correct ohms that the tank was showing. The fuel gauge is autometer set to 4-86 ohms and the tank has a 0-90 ohms sender.

I retested with an almost empty tank with the engine off it was 6.25 ohms and the gauge was one line over empty perfect. After running the engine one or two minutes the gauge goes to full and then to 1/4 and stays at 1/4. I restarted engine with no gauge attached and the tank ohms bounce around and settle at 22.5 ohms which would show 1/4 on gauge.
So it definately a resistor problem when the engine is running. I tried an extra ground strap to the tank but that did not help.

What would cause the resistance to change when started.
Thank for any help

**CamaroAJ** · #2 07-13-2010, 02:46 PM

what happens if you ground it out it when its acting funny? since you would have zero ohms it should read below E. also what happens when you unhook the sending wire? pending on the gauge it should read past full.

also what do your test leads show ohm wise when you touch them together? i have seen them read as much as 20 ohms by them self when they should read zero ohms and that would be caused by bad leads or just a cheep DVM.

awesometool · #3 07-13-2010, 06:28 PM

Thanks,

I did not try grounding the gauge wire when it was running good idea. It is a 80.00 meter and we did try two different meters with the same results. I going to try it tomorrow

awesometool · #4 07-14-2010, 04:37 PM

I tried jumping the power to the aeromotive 1000 fuel pump and as soon as it turns the ohms change form 1.6 to 21.0 next I'm removing the return fuel line to test.

Vegas69 · #5 07-14-2010, 04:39 PM

Evidentally your fuel pump isn't grounded very well. I have mine grounded to the battery.

awesometool · #6 07-14-2010, 04:41 PM

thanks I try that first.

awesometool · #7 07-14-2010, 04:51 PM

Todd thank for the help that did it

Vegas69 · #8 07-14-2010, 04:55 PM

Great, I'm assuming you're running a relay?

awesometool · #9 07-14-2010, 05:44 PM

Yes there is a relay. I had run the pump ground to a grounding block used for the amps. I moved the ground direct to the battery and its perfect. The grounding block has 2 gauge to the - side of the battery but a lot of radio grounds run off it. thanks again.