Fuel Gauge Stopped working

[greenbean]

Fuel Gauge stopped working after sitting for a month or so. Here is what I have checked and are okay (note temperature gauge works fine):
1. Fuse on Green wire side is good
2. Instrument Voltage regulator has 12 volts on Green/Black wire (again temp gauge works)
3. All wires connected including the one at the fuel tank
4. All other items tied to the Green wire system, like wipers, temp gauge, heater all work fine.
5. I put a circuit tester on the one side of the Green/black tab on the guage (from the Voltage regulator) and it lit up bright.
6. I put a circuit tester on the gauge on the side (Green/black wire) that comes from the fuel tank, it lit up dim but the gauge needle then registered the 6 gallons that were in the tanks (note I triple checked this again, and again and again as it seemed interesting).

Does this mean I have a bad gauge

Russ

 

[junkman]

gauge

sounds like a bad connection between the tank and the gauge clean all terminals and I think you'll have it.

 

[Tom H]

I think I understand your step 6 to mean that the gauge reads 6 gal ONLY while the tester was connected to the test point and went back to zero each time you remove the test lamp. If so that tells you that the everything is working EXCEPT the sender in the tank. What is happening is the sender is an open circuit , but when you put the test lamp on your test point, the lamp has about the same resistance that the sender would at 6 gal, so it reads 6 gal. Double check, and wiggle, the green black wire connections at both the gauge and at the sender. If that does not fix it, I am 80% sure the problem is a poor ground INSIDE the sender device. It is quite easy for a little corrosion to occur where the pivot pin fits inside the housing of the sender.

BUT before you take it apart, I suggest you drive the car over some bumpy road and swerve the car a bit to get the fuel to slosh around and cause the sender to move a bit. And / or fill the tank to move the sender. I'll bet that fixes it!

For more details and a photo of the sender, see my post #20 on this thread:

http://www.sunbeamalpine.org/forum/showthread.php?t=15723

Tom

 

[greenbean]

Tom ---
I went an added 3 gallons to the tank and did what you had said, but to no avail. So I took my continuity checker and the gauge now registers 9 gallons which is what is in the tanks when I "stick-measure". So I, know I would think that I would know that the float is not stuck --- is it possible that the gauge has lost some internal ground or something. Is there any way to do a "shade-tree-bench-check, or do I need to send it out to be checked?

Russ

 

[chazza]

A useful way to guarantee a good earth (ground), is to make a cable which connects to one of the mounting screws on the sender-unit and connect the other end, to a suitable point on the body of the car.

If it doesn't improve things, at least it will show that the problem lies elsewhere. Relying on a good earth through the screws of the sender unit and then through the fasteners holding the tank in place, can sometimes be problematic due to paint, rust and dirt getting in the way,

Cheers Charlie

 

[Tom H]

I don't understand what test you did with your "continuity checker". Do you mean your test lamp? or did you use a different device? A "continuity checker" usually has a battery and a buzzer in it, and is not usually used to test a circuit with power already in the circuit.

Did I understand correctly before that when you put your test lamp on the gauge terminal, it read 6 gal? If so that pretty well confirms that your gauge is working.

If you are still unsure, one easy way to test the gauge is to swap it with the temp gauge. Just swap the wires from the temp gauge with the fuel gauge. They are identical, except for the dials.

I am still 80% sure that your problem is in the fuel sender. You may have to remove it and clean up the little corrosion as I noted in the thread I linked earlier.

Chazza does have a point that the problem could be the ground on the sender, but the sender body is pretty well anchored to the tank body. And the tank has several solid anchor points to the chassis, so it seems less likely to be a bad ground there. I think the bad ground is inside the sender.

By the way, once you get your gauge working you'll need to figure out why the supply to the gauges is 12 V. It should be 12 V turning On and Off about 2 times per second, if you have an original Voltage Stabilizer", or a steady 10 V if you have modern solid-state replacement Stabilizer,

Tom

 

[greenbean]

Tom ---
I am agreeing with you that it must be the sender as I did swap the temp with the fuel gauge and it registered just fine, plus i ran a jumper wire from the sending unit to the gauge and the gauge still did not register. So now I am off to take the sending unit out of my Series V. It looks as though if I removed the trunk spring I could get to the plate that holds the sending unit in and then maneuver the sending unit out --- does that sound possible?

Russ

 

[Tom H]

Russ, I, personally, have never removed a sender from a tank that is installed, but I am pretty sure others have. It really takes just a couple taps on a tooth on the flange and it will probably be loose.(lefty loosey direction).

But please clarify for me the electrical tools you used. Was it a simple test probe with a lamp in it, or was it a "continuity checker" with a battery in it? Or do you have and used both types?

And be sure you read my post I linked earlier on how to clean up the pivot on the sender.


Tom

 

[greenbean]

Tom ---
It was a simple test probe with a light, on one end is a point you touch to the hot side, on the other end is a clamp that you connect to a good ground and when you have a good circuit the light bulb lights up bright. Which is what I had on the Green/Blk wire coming from the Voltage regulator. The Green/Blk wire from the Fuel tank float was a dull-yellow light, and when I touched it to this wire clip on the gauge, the needle would rise up to the level of the tank.

 

[Tom H]

Russ, thanks. That's what I thought from your first post where you called it a circuit tester and that it lit up. That's a great way to trace voltage in a circuit. But in your later post you referred to it as a "continuity checker" which is a different item, which includes a battery powered buzzer, which is used to test un-powered wiring.

Your experience provides a neat way to test the Temp and Fuel system. People have often asked for a quick way to test the gauges and system. You just showed us that a typical circuit tester lamp would cause the gauge to read somewhere about half scale, assuming the sender was open.

Tom

 

[Jimjordan2]

Yes, you can remove the sender with the spring removed. Just got done doing that.

 

[greenbean]

Thanks to all for your help. It ended up being the plastic Fuel Float that I had gotten a few months ago got a crack in where the holder ring is attached --- so the float was full. I had gotten the float from Moss Motors. This time I went with the Brass Float , hopefully no more issues with the float and happy motoring for the rest of the summer and fall!!!

 

[Alpine66]

If I remember correctly on my V, the sender merely grounds the gauge, varying the resistance corresponding to the position of the float.
To test the wire, remove it from the sender and ground it with the key turned on, and then it should move the gauge, may take a minute as these react slowly I believe.

Someone correct me if I'm wrong.

 

[Tom H]

66, yes, you are correct, just grounding the wire at the sender should cause the gauge to go past full scale. What Greenbean found out is that if you insert a typical small 12 V test light between the connection and ground the gauge will read about half scale.

Tom

 

[Alpine66]

66, yes, you are correct, just grounding the wire at the sender should cause the gauge to go past full scale. What Greenbean found out is that if you insert a typical small 12 V test light between the connection and ground the gauge will read about half scale.

Tom

Yes, my post was for testing all the way to the connection at the tank to identify or eliminate the wiring, gauge and power up to that point.
It was unclear to me where he was testing the wire,at the gauge or tank.

Glad it was solved, too bad it was a newer part.