Fuel Gauge Troubleshooting

[David Discenza]

Hello! New member and first time Catalina owner.
We just took possession of a 1993 C34. During the seat trial, the fuel gauge was working. Now that I own the boat, it's not. I've done some preliminary troubleshooting with these results:
- I checked the voltage with mu multimeter at the instrument and it read 12.5 volts, same as the battery meter.
- I disconnected the sender wire and used a screwdriver blade to short across the sender input post and the ground post. The needled jumped to the 1/2 position on the gauge.
- I checked the resistance of the sending wire at the instrument. It read zero ohms at all settings of my multimeter
- I checked the resistance of the sending wire at the fuel tank. It read zero ohms at all settings of my multimeter

The needle of the gauge is all the way to the left, off the scale of the gauge. When I turn the ignition key, the needle jumps a millimeter or two and goes right back to all the way to the left, off the scale of the gauge.

I want to see if the repair shop at my marina has a fuel gauge that's known to be good. If they do, I'll temporarily connect it and see if it works. If it does, then it's definitely the gauge. If it doesn't could it be the sender as well as the gauge?  I'd appreciate the thoughts of others on this problem. Thanks to all who reply.

[Ron Hill]

David : A while back I put the Teleflex and Seaward fuel gage trouble shooting steps on this Message Board.  They maybe in WiKi?

A thought

[David Discenza]

Ron,
I'll look for it.  Thanks.

[KWKloeber]

David,

Welcome to the CTY family.

I had put the gauge t/s guide in the engine > electrical wiki topic. 
http://c34.org/wiki/images/3/34/Gauge_Troubleshooting_Steps.pdf
It gives the resistances of the fuel sender so you can check it at empty and full . 
Float empty the R should be about 240 ohms.  Full, the R should be about 33 ohms.

See below:

- I checked the voltage with mu multimeter at the instrument and it read 12.5 volts, same as the battery meter.
- I disconnected the sender wire and used a screwdriver blade to short across the sender input post and the ground post. The needled jumped to the 1/2 position on the gauge.

If you ground the S terminal on the gauge it should pin high. Your gauge is toast (caveat - based on your test.)
If you disconnect the sender wire the gauge should pin low.

- I checked the resistance of the sending wire at the instrument. It read zero ohms at all settings of my multimeter
- I checked the resistance of the sending wire at the fuel tank. It read zero ohms at all settings of my multimeter

Checked ohms from sender to tank body, I presume?  Or to ground?
Make sure the tank bond wire is intact and low resistance tank to battery negative -- or take your ohm reading to a known good battery negative location.

The needle of the gauge is all the way to the left, off the scale of the gauge. When I turn the ignition key, the needle jumps a millimeter or two and goes right back to all the way to the left, off the scale of the gauge.

With the gauge way left (zero-ish) it indicates that there is infinite resistance in the S circuit.  In other words a disconnected S wire.  It doesn't make sense that the float reads 0.0 ohms -- then the gauge should be reading right (way high-ish.)

[mainesail]

This article can help you in testing the sender.

https://marinehowto.com/testing-a-marine-fuel-sender/