chaseincats

Gas gauge wire corrosion?

    Recommended Posts

    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

    Share this post


    Link to post
    Share on other sites

    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/

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites

    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?

     

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites
    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? 

    Share this post


    Link to post
    Share on other sites
    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?

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites

    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

     

    Share this post


    Link to post
    Share on other sites
    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.)

    Share this post


    Link to post
    Share on other sites
    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.  gas float.jpg

    Edited by crayZlair
    clarification
    • Like 2

    Share this post


    Link to post
    Share on other sites

    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.

    Share this post


    Link to post
    Share on other sites
    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.

    Share this post


    Link to post
    Share on other sites
    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

    Share this post


    Link to post
    Share on other sites
    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.  gas float.jpg

    Same idea as a toilet bowl adjustment.

    2008-01-25_090040-TreeHugger-plumbing.jpg

     

    • Like 1

    Share this post


    Link to post
    Share on other sites
    On 5/23/2020 at 12:57 PM, siteunseen said:

    Same idea as a toilet bowl adjustment.

    2008-01-25_090040-TreeHugger-plumbing.jpg

     

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

    Share this post


    Link to post
    Share on other sites

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

    Share this post


    Link to post
    Share on other sites
    1 minute ago, SteveJ said:

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

    By that you mean straighten the arm, right?

    Share this post


    Link to post
    Share on other sites
    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.

    Share this post


    Link to post
    Share on other sites

    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.

    1-left-float-empty.jpg

     

    • Like 1

    Share this post


    Link to post
    Share on other sites

    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). 

    Share this post


    Link to post
    Share on other sites

    The tank isnt dented so I just think its that I need to bend it and yep, the tabs are lined up.

    Share this post


    Link to post
    Share on other sites

    Create an account or sign in to comment

    You need to be a member in order to leave a comment

    Create an account

    Sign up for a new account in our community. It's easy!

    Register a new account

    Sign in

    Already have an account? Sign in here.

    Sign In Now