Gas gauge wire corrosion?

[chaseincats]

Hey guys I'm at a bit of a loss here.

Problem:

• My gas gauge is correct until it reaches the 1/3 full mark.  At that point, the needle will fall to an empty tank reading within a few miles.  An empty tank reading at that time denotes 6 gallons remaining in the tank (if i take it immediately to a gas station, I will be able to put ~12 gallons in each time).  

Steps taken:

• I installed a new fuel sending unit from zcardepot which oddly didn't fix the problem.  The only thing this fixed is my gas gauge needle slightly wiggled around a millimeter or 2 continually with the old unit - the new sending unit fixed that.
• Swapped out the dash gauge with a spare which gave more or less the same result (the other gauge read 1/8 full instead of empty).
• Went through each connector via the factory service manual and gave each a good blast of caig de-oxit - that said, every one of those connectors looked brand new.
• I've tested the gauge by filling the car up when it reads 3/4 full and the proper gallons are in there so it really does seem to be a problem only within the 1/3 to empty range of the tank.

So I'm at a bit of a loss here because everything looks good including the connectors.  Could there be some corrosion inside the wiring somewhere?  Do these gauges fall out of calibration?

 

Any ideas?

-chase

[heyitsrama]

I never tried to take my car all the way to empty. I recall the friend time I drove my friend around in my “new car” I ran outta gas, we had to walk back to her place to get a jerry can.

 

see this thread on hybridz

Quote

My 73 reads "empty" at 12 gallons as well. As an experiment, I took my spare gas can with me and drove until the car ran out of gas. It took 15 3/4 gallons to refill (2.5 gallons from the can, the rest at the gas station). It turns out that true empty on my car doesn't occur until the needle is pointing towards the left corner of the bottom of the "E". That's a long way (4 gallons!) after it hits the left-most side of the scale.

https://forums.hybridz.org/topic/64752-240z-gas-tank-capacity/

[heyitsrama]

With that being said I just realized that my 260z also operates about the same way, is ~6-7 gal to get it from empty to a little past the midway point. Now it’s gonna bother me.

[Captain Obvious]

Chase, So your gas gauge works fine for all situations except when the tank is about 1/3 full? If that's the case, then I'm having a hard time coming up with any answer other than a problem with the sender unit.

I know you replaced that and it didn't fix the problem though, right? Does the new replacement act just like the old original sender unit?

 

[crayZlair]

Try bending the float arm "down" a little bit. This will cause the float to start moving up off of "empty" with less gas in the tank.

[chaseincats]

1 hour ago, Captain Obvious said:

Chase, So your gas gauge works fine for all situations except when the tank is about 1/3 full? If that's the case, then I'm having a hard time coming up with any answer other than a problem with the sender unit.

I know you replaced that and it didn't fix the problem though, right? Does the new replacement act just like the old original sender unit?

 

Yea it acts exactly the same which is frustrating.  You don't think it could be resistance in the wires when it gets to a certain amperage.  Or would it be that if there was resistance in the wires it would be inaccurate all the way through the tank range? 

[chaseincats]

48 minutes ago, crayZlair said:

Try bending the float arm "down" a little bit. This will cause the float to start moving up off of "empty" with less gas in the tank.

The sending unit is literally brand new and so its configured to factory spec.  Wouldn't bending it undo that?

[siteunseen]

I bent my brand new one to match the OE one from 1972. My reading around suggested it was straighter out of the box. Gauge works like my 280's does. It takes forever to get to half a tank from FULL then drops like a rock on that other half, but all my cars seem to do this.

[chaseincats]

Just now, siteunseen said:

I bent my brand new one to match the OE one from 1972. My reading around suggested it was straighter out of the box. Gauge works like my 280's does. It takes forever to get to half a tank from FULL then drops like a rock on that other half, but all my cars seem to do this.

Well that makes me feel better.  The angle you bent it to fixes this more or less?  If it does, could you take a picture of your angle and I'll bend it this afternoon.

[siteunseen]

It's in the tank and I'm not taking it out, sorry. But I remember now a little more of my research in 2012. Nissan used that sending unit in different cars and forklifts.

I'll look for some images real quick and post one if I can find something.

[siteunseen]

can't find a side by side image of the old vs new sender. I did find something I read about a set screw adjustment you might can do before installation. 

AZ-240z replied to a topic, click that

 

[Captain Obvious]

9 hours ago, chaseincats said:

Yea it acts exactly the same which is frustrating.  You don't think it could be resistance in the wires when it gets to a certain amperage.  Or would it be that if there was resistance in the wires it would be inaccurate all the way through the tank range? 

No, I think if it were resistance in the wires (and connectors), it would do what you said... Inaccurate through the whole range.

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