Problem with fuel gauge

[denpat]

I purchased a new Alumacraft Dominator 175 and decided I wanted to add a trim gauge and a hour meter. I was very difficult getting to these gauges. I was having problems with the volt meter and the fuel gauge and found that they weren't properly grounded. In doing my testing I accidently touched the ignition wire to the ground instead of the sender to the ground. This caused the fuse to blow, which in turn burnt out the gauge. I have purchased a new gauge and installed it, but it does not read correctly. The needle moves but not even up to empty. I know that there is 12 gallons of gas in the tank so sound read around 1/4 tank. I have tested the new gauge and find it to be ok. I don't think I could have done anything to the sending unit. I am still trouble shooting this problem, but could use so good input.

By the way these are Teleflex lido gauges.

Thanks

Denpat

 

[Bondo]

Re: Problem with fuel gauge

I have tested the new gauge and find it to be ok. I don't think I could have done anything to the sending unit.

Ayuh,... Does the sender have a Good solid Ground,..??

 

[denpat]

Re: Problem with fuel gauge

I have not check that yet. I will be checking that end of the problem today. When I bought the boat I had the dealer install a radio and my 3 bank charger and I'm not sure they didn't cause the problem. I know the charger wire that goes to my cranking battery must run down beside the fuel tank somewhere, but I haven't pulled the floor to verify that. However, since in my trouble shooting this situation I did burn out the gauge so I feel the problem is in my hands. When I touched the ground to the ignition wire I am wondering if the current would back feed down the sender wire to the sending unit, possibly frying it. I have done enough electrical work to know that a bad ground can cause many weird things to happen.

 

[denpat]

Re: Problem with fuel gauge

I have one other question. In checking the resistance from the sending unit can this be done at the gauge. Can I measure the resistance by taking the sending wire off at the gauge and using the ground from the gauge also. What would this do to the resistance measurement?

 

[Silvertip]

Re: Problem with fuel gauge

Yes - you can check sender resistance at the gauge as follows:
WARNING: Key off and stay away from +12 volts.
1) Disconnect the sender wire from the gauge.
2) Measure between the sender wire and a known good ground.
3) Full tank should measure about 33 ohms -- 1/2 tank should measure about 109 ohms, -- empty should measure about 240 ohms. Anything in between you'll have to do the math. Those are all approximate numbers so you can expect 10 - 15% difference and still be perfrectly ok.

If you show infinity (open circuit) either the wire is open, the sender is open, or you lack a good ground (either up front or at the sender).

Here is a diagram of the fuel gauge circuit.