Fuel gauge vs gas tank sending unit??

[dkassulke]

This concerns a 1976 280z: Last time I filled the tank I noticed the fuel gauge only read 1/4 full. How do I determine if I have a faulty fuel gauge or gas tank sending unit?? If I need to have fuel gauge rebuilt where could I have that done. If sending unit issue: repair/clean or replace. Where would one find a gas tank sending unit for '76 280z?? Thanks for any input!

[Mikes Z car]

Here is a related thread that may help

http://www.classiczcars.com/forums/electrical-s30/52215-curious-problem-my-gauges%3B-question-about-wiring.html

[SteveJ]

If it's the fuel gauge, you could try Bob's Speedometer.

I believe there are procedures to test the sending unit in the FSM. The gauge is trickier to test. I don't have time at the moment to describe testing it.

I am not sure where to get a sending unit refurbished. They are NLA.

[siteunseen]

I'm having trouble with my fuel gauge and need some help. Brand new sending unit with new connections on it. I shorted the 2 wires together at the sending unit, no movement at the gauge. I tried to measure the voltage at the yellow wire without any luck, it was all over the place on my meter. Then I clipped a cheap test light onto it, it blinked, on/off/on/off/etc. So it's getting some power just not a steady supply. I'll try the ground under the cigarette lighter Mikes Z pointed out. Any other ideas before I take the gauge out?

Thanks for any help,

Cliff

[SteveJ]

Cliff, remind me in a couple of days. I'm taking next week off from work, so I'll be playing with car stuff. I can do more of a write-up on the gas gauge.

[Captain Obvious]

I don't think the yellow is supposed to have a steady supply. I think the blinking is part of the way the gauge works. There is a bi-metallic strip in the gauge (kinda like your thermostat in your house) that makes and breaks the current to the sender as the strip is heated and cooled.

If you ground the yellow wire back at the sender, the gauge should read F. But it won't happen immediately. The gauge response is pretty slow. Ground it and wait thirty seconds and then look at the gauge maybe?

[SteveJ]

The good Captain is right. I want to see if I can hook up a scope to create a visual of it.

[Captain Obvious]

Phew. Good. Been a while since I looked into any of this and I was hoping I was remembering it right!

At the risk of going off the geek end, here's a pretty good description (I think) of how the gauge works. It's not a Z (Jeep I think), but I believe the principals are the same:

The new Gauge Page

[siteunseen]

So short the black with the yellow, get in and turn the switch to ON and see what happens. Or should the car be running? I didn't do that yesterday because I had it up on a stand, passenger side only.

I'll short them at the sender and crank the car and wait until 1 beer is drank, I'll drink it slowly for the 30 second time suggested.

I'm so dang stupid! I've got the same car sitting 6 feet away, I'll see when it's gauge starts moving, ON or cranked and on ON.

Edited June 26, 2014 by siteunseen

[siteunseen]

I think I've found the problem. While trying to get to rear of the cigarette lighter, which I can't without removing the heater control panel, I noticed the lens on the gauge had a gap on the right side. So I've double over some Gorilla Tape and pulled the lens off the aluminium divider between fuel and amp gauges. The needle moved! So I'm thinking the Barners I bought this car from, tapping on the gauge too hard has messed it up. The sending unit was frozen with rust and I guess they thought the gauge was the problem. I'll let y'all know what happens. And respect to EScanlon for the write up on removing that panel, RIP sir.

[siteunseen]

This's the gauge hanging upside down without any pressure from that aluminum trim behind the glass and that's about right as I only put 4 gallons in yesterday after the tank refurbish and drove it 25 miles. I'm gonna check the gauge bulbs before I put it all back, it's a Yoga style PITA, I don't do Yoga.

THANKS

[Captain Obvious]

Excellent! So with the aluminum trim bezel not restricting the needle, what happens when you short the yellow to the black at the tank?

Time for another beer!

Hey, I really like working with you!! !!