I recently installed a FiTech throttle body system on my 81 vet. I used the 82 Fuel sending unit so that I could mount the fuel pump as the 82 unit had the provision. Since making this change my fuel gauge has been consistently in the 5:00 o'clock position. Does anybody know if the resistance on the 81 and 82 are the same between the full and empty positions. I would appreciate any advice that you can give me.

 

Resistance is definitely the same. Is the float jammed? Stuffed up your wiring?

 

Doc I have had the sender out on other time after the initial commissioning. The float is not stuck for sure. However I want to conduct a resistance check to ensure that sender is okay before tackling the gauge.

 

I used the 82 sender also for my fuel injection system and it does read correctly it seems. I have about a 1/4 tank of fuel in it and that's what it seems to be showing. I can watch it go up on the gauge as fuel is added so it seems to be functioning correctly. Do you have a ground wire attached to the sender housing itself? I have two wires going into the tank, one for fuel pump power, one for the sender and then the ground wire on the sender itself going to a chassis ground point. Any pics of how you have it wired?

 

So you will have a few problems using the 82 Sending unit vs 78-81 sending unit. Here are some pictures showing the difference.
This is the 82 Sending unit. Notice the float location to the right. This is a picture of the factory float arm.

Here is a picture of the unit inside the tank. @ items to note.
1. The float level arc doesn't follow the same path. center point of the float is different than the 78-81 units. Flat part of bar. (see 78 unit below)
2. The length of the float will possibly hit the tank rib on the right side. Thus restricking full motion. (red arrow).
you may get 2 readings. Empty or stuck at point, or range from full to some value near 1/3 full.

This picture shows I had to bend the float lever to allow full range of motion. But as you can see when the float is at empty there is still plenty of fuel in the tank. But the fuel pump inlet is to high from the buttom of the tank.
When the tank is greater than 3/4 full, the float is to short (arc path) so it hits full well before the tank is full, and will read past full.
Here is my 78 unit in tank.



Notice the float center point location. Vertial mounting point allowing arc from empty to full. Much better range. Also note the fuel pickup point which is lower in the tank.

Here is a picture of the 82 Sending unit and how much I had to bend the float to create a full range of motion in my tank. (Clear the rib on the right side)

While this works, but the accuracy of fuel in the tank is not linear. Reads full for many miles, then starts to rapidly fall to emply. Hits empty when it has about 15 liters of full.

Using a holley hydramat may allow you to run the engine, but the guage will read empty.

I bent the float to estimate (show) when the fuel level matches the fuel pump inlet point.


This is not a great solution, but works for EFI on the cheap. Just live with a few adjustments and re-learn what the guage is telling you about fuel levels.

Please test the range of motion before installing the gas tank into the car. I missed this the first time as noticed a always empty tank. Then forced the float past the rib to get full to about 1/3 tank at best.

I connected a ohm meter to the sending unit while rotating the tank to similate fuel levels. My 82 unit went from 0.8 ohms - 96 ohms. Similar to the factory 78 unit.

 

Many Thanks for your insightful explanation. I did not check the centre of rotation as I assumed that the two tanks and sending unit would have been the same. As I still have the old sending unit I will find time to empty the tank and remove and compare the floats. Many thanks for your time to respond.

 

Do you have access to a Borescope. That is how I first discovered the float being jammed. If you can use a Borescope to see where the float is sittng. Or use a ohm meter and connect from the middle wire to ground of the sending unit. This will give you the ohm reading of the sending unit. Should be somewhere between 0-90 ohms. Also you stated gauge pointing to 5 o'clock position ? do you have a picture to post. 5 o'clock is not in the range for any ohm reading. Indicating a gauge problem. Then I would test via this link.
1968-1982 Corvette Fuel Gauge Test | Willcox Corvette, Inc.

 

I do have a boroscope which I will attempt to put it into the tank. Currently I have about a half tank of fuel. I will try and get it pumped out today. Once again thanks for your input.

 

Yesterday I emptied my tank and removed it from the car. I removed the sending unit and checked the resistance over the full range. 0 to 96 ohms. I replaced the sending unit into the tank after attaching a string to the float. I was unable to raise the float. After measuring the 1981 sending unit I compared it against the 1982 unit. As advised it has a different location for the pivot point. I had to bend the float arm until I was able to get it to travel the full distance which I had previously marked on my string. Once I have re installed the tank and gauge I shall post the photos of the differences. Once again I appreciate the comments of people on this Forum.

 

I have attached some photos of the difference between the two sending units, 81 / 82.



















81 Sender showing float fulcrum

81 Float fulcrum

82 after bending float arm

82 float arm bent.

82 Float fulcrum point

 

This is the measurement that is important where the buttom line represents the fuel level vs the gas inlet housing.

Hold the sending unit at the same angle as mounted in the tank to see what the fuel level in the tank will read as empty.

Based on the picture of the float arm (bent upward from factory) the fuel level will be higher but still the gauge will read empty.

Best option is to simulate the angle of the sending unit and match the float end to be at the fuel pump pickup level. That way when the gauge reads empty its because the fuel level is at the fuel pump input level.

My float arm is bent opposite to yours. Arc up and then down. Yours is arced down then up. Your setup will read empty with more fuel in the tank.

 

if you had fuel in it, should it have not gotten stuck at the bottom?