Fuel sending unit question

[andyroo]

I've got my fuel tank in at a shop to double check a leak and one of things we were looking at was the fuel sending unit.

Before, I wasn't getting a reading at all on my fuel gauge or temp gauge. Firstly I replaced the voltage regulator.

I then had a reading on my temp gauge (yay!), but still nothing on the fuel gauge (boo!).

So I was thinking my fuel gauge or the sending unit were faulty.

My mechanic bench tested the sending unit. He was getting a consistent reading up to about 3/4 of the way, and then nothing. I wasn't there to see it so I don't have much to go on other than that.

Does that make sense? Should I replace the sending unit? Alternatively, anyone have an extra 1968 fuel gauge?

[caraddict]

For the most part the element on the sending units are either completely open (which is bad) or they will read anywhere from 83 ohms at empty to 16 ohms at full and they generally do not go bad at one end or the other. Sounds like yours may need to have the wiper and the element cleaned up which is pretty easy to do with the unit out of the tank. You can also add a little more tension to the wiper by bending it toward the element but don't go too far as too much tension will eventually trash the windings.

The fuel gauge's very rarely go bad but if you want to ohm it out then it should read about 45 ohms so unless it's reading open or giving you a very high reading then it's probably good too.

Jon

[andyroo]

Thanks for the response. My thought was that the unit would either work completely or not like you said.

Since my sending unit was pretty gunked up and crappy due to a bad o-ring, I'll clean it up, and reassess.

I'll check the gauge when I get a chance. It's never read anything other than empty since I've had the car (2 years) and I used to think that was just the fault of the regulator.

- Andy

[Nissanman]

Use a good quality electrical contact cleaner and dose up the wiper and windings well.
Over the years, the wiper may have worn through the winding and broken the continuity.
A thorough check with an ohm meter along the length of the wire wound resistor will determine any break.
BTW here are the specs. of the fuel sender as used in my '65 SP310 as determined out of the tank: -
˜ 90 Ohm Element
˜ 84 Ohm Empty
˜ 10 Ohm Full.
I don't think the Empty value is technically correct since the float may not actually go down that far, it may hit the bottom of the tank before it reaches 84 ohm.

[jimmyg]

Thanks for the help the first sending was bad but the one from my donor car works after spraying it down with electrical cleaner a few times. Thanks again Jim Sure glad I did not have to buy one or go the marine route.