4 hours ago, Captain Obvious said:

I'm also having trouble explaining how bending the arm could fix this. (But full disclosure, I've never messed with the sender units.)

Pardon my crude drawing. Lets assume for the sake of explanation that the float arm at its lowest position is at 45 degrees from level. This will give you an empty reading on the fuel gauge. If you bend the float arm down slightly, it will effectively change the angle of the arm at the pivot point, causing the fuel gauge to read somewhere above empty. The fuel gauge may show full longer, but the main purpose of the fuel gauge is to let you when you are empty, correct? Any reading above empty is not as critical. 

Edited May 23, 20204 yr by crayZlair
clarification

8 hours ago, Captain Obvious said:

SOUNDS like the sender unit has a dead spot below 1/3 tank, but I'm having trouble explaining the exact same behavior with two different senders.

I had one sender that had a little blob of something on the coil wires so when the slider went over top of it there was no signal but worked on either side of it.  I used a rounded Xacto blade to carefully scrape away the blob.

2 hours ago, grannyknot said:

I had one sender that had a little blob of something on the coil wires so when the slider went over top of it there was no signal

Exactly. That's what it sounded like to me, but I'm having a hard time believing that he got two senders with the same blob in the same location.

3 hours ago, Captain Obvious said:

Exactly. That's what it sounded like to me, but I'm having a hard time believing that he got two senders with the same blob in the same location.

Right - both senders had clean coils (I cleaned the first one and the second one was brand new) and I'm having the same issue in the exact same portion area of the gas gauge.

For reference this is the sender I got: https://zcardepot.com/collections/fuel-sending-units/products/copy-of-fuel-tank-gauge-sending-unit-sender-240z-260z-280z-70-78

11 hours ago, crayZlair said:

Pardon my crude drawing. Lets assume for the sake of explanation that the float arm at its lowest position is at 45 degrees from level. This will give you an empty reading on the fuel gauge. If you bend the float arm down slightly, it will effectively change the angle of the arm at the pivot point, causing the fuel gauge to read somewhere above empty. The fuel gauge may show full longer, but the main purpose of the fuel gauge is to let you when you are empty, correct? Any reading above empty is not as critical. 

Same idea as a toilet bowl adjustment.

 

On 5/23/2020 at 12:57 PM, siteunseen said:

Same idea as a toilet bowl adjustment.

 

So when I bend the arm, am I straighening the bend or bending the arm further in the same direction?

If you bend the arm down, it will register E later.

1 minute ago, SteveJ said:

If you bend the arm down, it will register E later.

By that you mean straighten the arm, right?

6 minutes ago, chaseincats said:

By that you mean straighten the arm, right?

No. I am saying "bend the arm down". If that happens to straighten the arm, that is coincidence. The point at which you attempt to bend is entirely up to you.

I agree with Steve. If you bend it down, more toward the bottom of the tank you'll get an empty reading much sooner.

This is not a Z tank but for you to get an understanding of what I'm saying.

 

gotcha, thanks guys, ill straighten the arm then

Sherlock Holmes here.  

Since changing the sender and the dash gauge produces the same result, there is only one thing in common with both scenarios. The tank itself. (other than the wiring)

There is therefore, something in the tank that is touching/interfering with float movement at that 1/3 position. Big dent in the bottom?

About the only other thing about the tank is the rotational orientation of how you are inserting the sender into the tank. There is a little tab on the tank, and small gap in the sender ring that line up? 

Really scrapping the bottom of the tank/barrel here...

Another test, If you move the sender arm in free air with it out of the tank, does the gauge respond in the same way? (have to connect a ground wire between the sender body and the tank).