Gas gauge fluctuating

[Steve_avanti]

I have a 77 Avanti.  I filled the gas tank & it only read 1/2.  As I drove the gauge bounces between 1/2 & 1/8.  Recently I ran out of gas when the gauge read 1/8.  Is there a ground that is typically bad?  Are these gas gauges inherently faulty?  Any insight is appreciated.  Thx!!

[IndyJimW]

If you can get to the sending unit you can unplug the two wires and use resisters to test the gauge.

I believe 240 ohms is empty and 33 ohms is full, I could be wrong.

I use a 200,100,50 resisters to test the gauge positions. If the gauge works its the sending unit. If the gauge doesn't work its the gauge or wiring to the gauge.

Good luck,

Jim Wood

[Steve_avanti]

Today I let the gas tank run near empty.  Filled up @ Costco & the gauge went up above 1\2 to nearly 3/4.  First time gauge has read above 1/2 in a while. Could there be an issue with the float that's causing the inaccurate reading? Gauge jumps around quite a bit but read near empty when tank was close to empty. 

[Gunslinger]

In two different Avantis (a '63 and a '70) I had similar experiences where the gauge would only go so high even when I knew I had a full tank.  Each time replacing the fuel tank sender cured the issue.

If you have the shop manual it gives instructions on how to test and determine whether the tank sending unit or the gauge is at fault.  

[ALAGENT99]

Hello, I also have the same issue as Steve, on my '78 Avanti II. I Fill the tank and it only reads a bit over 1/2 or 3/4 but never full, gauge flutters radically when driving. Is there 2 problems or just one ?  Gunslinger..the fuel sending units on both your Avanti's cured what issue ? The fuel gauge not reading the correct amount of fuel in the tank or the fluttering gas gauge , or both ?

I will try the method Mr. Wood is suggesting to determine which one, gauge or sending unit, is at fault. It seems to me that there are 2 separate issues here, 1- gas gauge not reading fuel level accurately and  2- the flutter of the gauge needle when the car is moving. Does anyone know if it is one or two problems ?

After some research and asking a few automotive inclined friends, we found this site that has an electronic fix to eliminate the gas gauge flutter. If / After I can find out if this is one or two issues I can proceed with the correct fix.

Here is the website I found...... This product is also sold on E-BAY,  SN34

   AL POLO   1978 Avanti II RQB2802

https://www.classicinstruments.com/userfiles/files/SN34%20Fuel%20Link%20Installation%20Manual%20Revision%20062515.pdf.

                 

 

[Gunslinger]

Yes...each car had the same issue...bad tank sending unit.  Neither gauge fluttered as you describe...they simply would go slightly over halfway to full but no more.