Gas guage doesn't work-- bad guage?

[Jeff-in-PA]

Last fall I purchased a 1993 Starcraft 24' pontoon boat. One of the known problems was a gas guage that did not work.

Here's what I've checked so far.

1) Checked for continuity at the tank sending unit. I did get a reading showing some resistance. I took this to mean that that the unit is working. I did check it with the wiring attached but the key off.

2) With a battery showing 12.0 VDC ( which will be replaced) , the key on, I got a reading of 2.19 VDC at the sending unit, a reading of 9.6 volts at the gas gauge itself but no needle movement at all.

Does this sound like the gas guage itself is bad? I did find a NOS unit that matches exactly on ebay for just over $30 shipped.

If not, what should I check next?

Thank you very much
Jeff

 

[Jeff-in-PA]

Re: Gas guage doesn't work-- bad guage?

Anybody have a clue?

 

[Dunaruna]

Re: Gas guage doesn't work-- bad guage?

Turn ignition 'ON' (not running). Remove the centre sender unit wire, touch it to ground while looking at the gauge. Does the gauge go to full?

 

[Silvertip]

Re: Gas guage doesn't work-- bad guage?

Any resistance checks must be made with the device "out of the circuit". To test the sender it must be disconnected from the the gauge. If you have an idea how much fuel is in the tank, measure sender resistance. If the tank is half full, it should measure about 109 ohms. Sender resistance varies from 30 to 240 ohms (full to empty). In my experience the gauge is rarely the problem. Wiring or the sender is normally the issue.

 

[Jeff-in-PA]

Re: Gas guage doesn't work-- bad guage?

Turn ignition 'ON' (not running). Remove the centre sender unit wire, touch it to ground while looking at the gauge. Does the gauge go to full?

I removed the center sending wire, turned the key to "on" ( also turned on the master switch for the panel on the dash just in case ) and touched the wire to both the ground wire and the top of the sending unit.

The gas guage did NOT move at all.

Any other suggestions?

Thank you very much
Jeff

 

[Jeff-in-PA]

Re: Gas guage doesn't work-- bad guage?

Any resistance checks must be made with the device "out of the circuit". To test the sender it must be disconnected from the the gauge. If you have an idea how much fuel is in the tank, measure sender resistance. If the tank is half full, it should measure about 109 ohms. Sender resistance varies from 30 to 240 ohms (full to empty). In my experience the gauge is rarely the problem. Wiring or the sender is normally the issue.

I removed the center wire and got a reading of 125 ohms ( actually flucuated from 120 to 145 ohms ) while putting the leads on the sending post and grounding to the plate. I did leave the ground wire connected but did not touch the leads there ( did that alter my results? )


I did assume I had about a half tank of fuel and my reading seems to support this.

Any other suggestions?

Thank you very much
Jeff

 

[Dunaruna]

Re: Gas guage doesn't work-- bad guage?

Check that the gauge is receiving ignition voltage, check sender wire for continuity. If both these things are o/k, you have a bad gauge.

 

[sammy29926]

Re: Gas guage doesn't work-- bad guage?

hi,
if i were you i would take the sender unit out and read the resistance values while moving the float arm. If this checks out ok, time to check the fuel gauge. what brand is it? In my boat to reach the back of the fuel gauge involved polling the dash apart. Make sure your your conections are all clean. Read the resistance and the fuel sender unit and then at the back of the fuel gauge and see if the values are the same. this will eliminate any bad cable ect.
Good luck
Sammy

 

[Jeff-in-PA]

Re: Gas guage doesn't work-- bad guage?

Check that the gauge is receiving ignition voltage, check sender wire for continuity. If both these things are o/k, you have a bad gauge.

I disconnected the sender wire ( red wire) at the tank and ran a jumper from the sending unit to the back of the guage (red wire).

No reading at the guage.

I replaced the guage with a NOS one I purchased off ebay. Still no reading at the guage. ( but the new one does light up now--- small progress )

 

[gss036]

Re: Gas guage doesn't work-- bad guage?

Join the gang, I am having trouble with a new sender on a new tank. Got flusterated today and walked away from it until tomorrow.

 

[Silvertip]

Re: Gas guage doesn't work-- bad guage?

Is the ground wire at the sender actually grounded well on both ends. Check for continuity between the shell of the sender and the negative terminal of the battery. Open = bad ground. Continuity = good connection. You still have not verified that you have 12 volts on the "I" terminal on the gauge with the key in the RUN position. You then need to do a continuity test on the ground wire at the gauge to ensure the gauge is properly grounded.

 

[gss036]

Re: Gas guage doesn't work-- bad guage?

Silvertip, followed your advise, turns out I somehow lost a ground during removing and installing the new tank. Installed a new ground straight from the battery and everything now works.
Sure hope that Jeff-in-PA gets his going ok.

 

[P 0 P E Y E]

Re: Gas guage doesn't work-- bad guage?

Glad you found the problem.

To troubleshoot a fuel gage system, or any system you must first understand how it is supposed to work, IE wire connections and theory, so you can perform tests that will eliminate or narrow the possibilities.

In the case of a fuel gage and tank, you have ignition from the key switch or other switch which runs to the ign terminal on the gage. You have a ground on the gage which is for the light to work. On the gage you have a sender wire, this is the wire the runs to the sender on the tank...The center terminal on the round flange on the tank. It has a fiber insulator washer on it. This wire terminal is connected to a variable resister in the tank. full tank means float is at top less resistance means Gage should read full...When the float sinks, the resistance goes up (a less of a ground for the gage needle) The gage reads lower.

The Tank needs to be grounded too...as you found.