Jump to content
dmorales-bello

Perplexing "FUEL" light malfunction

    Recommended Posts

    11 hours ago, dmorales-bello said:

    2000 BC?

    The original reference to Darmok is from a Star Trek episode where they encountered a race that always spoke in metaphor. In that situation, you can understand the WORDS, but they really mean nothing unless you have a shared past experience.

    For example, you could ask "How is the weather?", and I could answer "Dave WM and Captain O riding in the Z."      :alien:     Haha!!!

    • Like 2

    Share this post


    Link to post
    Share on other sites

    Ok, hope this helps. I have both the original and a new ZCD unit on my bench. Removed the original and had the tank cleaned. 
    original unit has 4 holes on the side. Two right below the clamp and two more near the bottom both on opposite sides. The one from ZCD only has three holes on the bottom and a narrow slot on the top for the wiring. Here’s a video of my original 78 unit. Excuse the shaky hand. 

    Share this post


    Link to post
    Share on other sites

    CO, I did a little autopsy and carefully removed the plastic cap from my original thermistor. It looks like a very simple single wire resistance, and it was broken off the bottom (pic below) . I found no resistance in removal of the plastic cap and the end of the wire is bent up slightly and seems melted, so I'm quite sure I didn't brake removing the cap. I had also measured resistance with my dvm before removing the cap and got 0.0 Ohms reading.

    There are clear numbers on the side (see pics) and in contrast to the Z Car Depot unit, the 3 holes on the bottom are a bit larger in diameter, there are 2 additional holes on the sides, and the hole on the plastic cap is also larger. All the holes in the can are screened.[mention=1115]Mark[/mention] Maras suggested that perhaps the small holes on the top of the Z Car Depot unit weren't allowing air to escape and impeding fluid from rushing into the can from below when submersed. Before disassembly I experimented by comparatively dunking both thermistors in a clear glass container full of water. You could see air bubbles escaping readily from the top of the original unit as it went in. Not so with the ZCD thermistor. I had to shake it and tap it so air would escape. This validates Mark Mara's observation and what you and Dave had suspected at times, that maybe fuel wasn't getting inside the can properly.

    Please refer to one of my previous posts (# 82) for pics of the ZCD thermistor details.

    dcda4633a9aad7a9cdd5a001ad316aa9.jpg&key=c2f414d976a3ae3a693dd54faa7e43c6a144215100da597812f33fb51b49fa3c6a55012bb62ccfd6c197d55826ad2170.jpg&key=4f00fde8196eaa243ec2746452bdc97c79a3a044fa5ad977f5cdbd37d73f814d994ba87f908535c9f8cf4ba8ad678bfe.jpg&key=c0b95af73bdbedbe084bff7c96644505347e68d3b204bede501dd59f13ef6f384bf0f772f81a06e66a88477a78212e82.jpg&key=ffd41bc50b4ab580800e7f70c9eeda43b720baa8d6aa0805fcbcf8d2814652f1

     

    Sent from my SM-N950U using Tapatalk

     

     

     

     

     

     

    • Like 3
    • Thanks 1

    Share this post


    Link to post
    Share on other sites

    Dr. Dave,  Great photos of the failed original sensor. I did a little google searching on the internets for that part number (as I'm sure you did), and came up blank. I suspect that number is the part number for the ASSEMBLY, not just the thermistor. The thermistor itself is probably a small chicklet device with two leads on it. Just as a rough idea:
    29049-pt-large.jpg

    Looks like they soldered one lead to the wire embedded in the black plastic cap, and then they slid the thing together making sure the other lead poked out a hole in the metal can. Then they clipped the other lead off and soldered that other lead to the can. So in the end, you've got a one wired device with the other connection coming back through the chassis mount.

    You pulled one lead out with the black plastic end cap, but there should be more to it. Either the rest of the device has turned to dust as a result of the heat, or may still be stuck down inside the can. You pic is too dark for me to see inside the can, but there is more still in there.

    All that said, I think your analysis about the locations and sizes of the holes might bear some additional scrutiny. It seems unlikely to me that after being submerged in the fuel tank for hours, being shaken around by driving, that the air bubbles would not have worked themselves out of the ZCD sensor, but who knows. And if that sensor is sitting in a little air pocket, it could certainly behave exactly like the problem you're seeing.

    Share this post


    Link to post
    Share on other sites

    Yarb, I don't know if it's just me, but I couldn't get your video to work. It downloaded, but it was a blank screen. Probably a problem on my end, but can you do youtube instead of hosting it here on the forum?

    Share this post


    Link to post
    Share on other sites

    Maybe it's an iphone thing.  Here's my Windows 10 error message.  

    image.png

    Share this post


    Link to post
    Share on other sites

    I take that back, I did get it to work. Down load to desk top and then open.

    Edited by zclocks

    Share this post


    Link to post
    Share on other sites

    5 hours ago, Captain Obvious said:

    Yarb, I don't know if it's just me, but I couldn't get your video to work. It downloaded, but it was a blank screen. Probably a problem on my end, but can you do youtube instead of hosting it here on the forum?

    Here you go, @Captain Obvious. I uploaded @Yarb's video to YouTube. https://youtu.be/uQcu71wOkpw

    Share this post


    Link to post
    Share on other sites

    I’ll measure it tomorrow when I get back to the shop. I’ll measure my replacement from ZCD as well.

    Share this post


    Link to post
    Share on other sites

    SteveJ, thanks for putting the video on youtube for me. That worked. And Yarb, thanks for the video.

    So Dr. Dave, are you able to see the remains of the thermistor body down inside your outer housing? In this pic, you can see the solder blob on the outside where they made connection to the other sensor lead. You should be able to see some of that lead inside the case:

    dcda4633a9aad7a9cdd5a001ad316aa9.jpg&key

     

    Share this post


    Link to post
    Share on other sites

    interesting, my OE unit (which was not working) was missing the solder on the bottom, just a hole with a wire coming out that had been bent over. I did not notice any witness marks of old solder. My fix was to solder is so now it looks like the pic above (I presume the solder came off at some point, but hard to believe unless it was poorly soldered in the 1st place). If I have the reason to pull it out again I will prob solder the side to the clip as well to prevent the corrosion from forming there on the ground side as well. Another thing I want to do is to see if I can rotate it to find out how much of an effect orientation has on the gauge reading. This is the side loaded model not the top loader. will have to wait until the gas level drops obviously.

    Edited by Dave WM

    Share this post


    Link to post
    Share on other sites

    Good morning Cap'n O,

    I could not manage to snap a picture inside the can that would show what was in there with artificial lighting. With the help of some diffuse sunlight "by George I've got it". (movie reference. Trying to fit in! ).

    The only thing that's in the can is a fragment of the broken wire about 3/4" long sticking straight up from the bottom where it is still attached to a point of solder. That's it.

    Is there a chance some other component of the thermistor is embedded within the plastic cap?

    Hope this helps046ebd2cb2195c237ed2028a422648ee.jpg&key=d4ddc80eb3fa1bf81f12a3b917f977c2bef5e5cf05008e4c94386342991a1ec3

     

    Sent from my SM-N950U using Tapatalk

     

     

     

     

     

    6b17bb1187705bc4bacd7f3005a5efa4.jpg

    • Like 1

    Share this post


    Link to post
    Share on other sites

    hmmm maybe the OE unit is some kind of special NTC resistance wire (if there is such a thing) and not a separate component at all?

    I assumed it had to be a semiconductor of some kind, but maybe wire that is made with semiconductor material?

    I will be doing an autopsy of my spare defective unit later and reply back with results.

    Edited by Dave WM
    • Like 1

    Share this post


    Link to post
    Share on other sites

    Dr.Dave, Yep... There's the other end!

    DaveWM, I assume there used to be some sort of discrete component in there, but honestly I don't know enough about thermistors to answer your good question about just a length of wire that changed it's resistance with temperature. I guess it's a possibility? Maybe?

    I think it used to look something like this and the thermistor turned to dust:
    sender.jpg

    I also don't think there is anything buried inside the plastic end cap. I think that's just a device to transition from the thermistor lead to the flexible wire.

    Edited by Captain Obvious
    Updated sketch to show ferrule
    • Like 2

    Share this post


    Link to post
    Share on other sites
    11 minutes ago, Dave WM said:

    I will be doing an autopsy of my spare defective unit later and reply back with results.

    You ought to be able to de-solder the lead from the can and then just pull the plastic cap out with the thermistor along with it. (If the whole thing isn't too fragile by now...)

    Share this post


    Link to post
    Share on other sites

    Oh yes I see that end piece looks like a component of some kind was once there, I did not look at the bottom pic when I made the wire comment. Maybe a glass axial lead type.

    Edited by Dave WM

    Share this post


    Link to post
    Share on other sites
    11 minutes ago, Captain Obvious said:

    You ought to be able to de-solder the lead from the can and then just pull the plastic cap out with the thermistor along with it. (If the whole thing isn't too fragile by now...)

    yes I will do that, I have a solder sucker and to some solder braid standing by to use.

    Edited by Dave WM

    Share this post


    Link to post
    Share on other sites

    Yeah, I'm thinking that inside that black cap there is a ferrule crimped onto the end of the yellow wire. That ferrule would be crimped onto the wire at one end and have a flat disk with a small hole in the other. Stick the thermistor lead through the hole and solder it to the disk. Transition from the semi-rigid thermistor lead to the flexible stranded wire.

    Of course, I've never even held one of these things in my grubby hands so it's all speculation and analysis from afar.  LOL

    Share this post


    Link to post
    Share on other sites

    I updated the pic above to show more details about how I think the crimp ferrule is used to transition from device lead to wire.

    • Like 1

    Share this post


    Link to post
    Share on other sites

    some items I noted, besides the wide open reading on the thermistor, the slider on the fuel gauge is actually 2 sliding contact points. the one on the WW resistance element AND the one that grounds the slider arm to the metal of the sender. I was having some shaky readings with my analog VOM so I cleaned with some contact cleaner, a little scraping, and then some deoxit and it worked much more smoothy going from around 7 ohms to about 80 ohms full spread.

    back to the thermistor

     I tried various contact of the hot lead thinking maybe a corrosion point on the crimp from the wire to the terminal on the sending unit no joy, I cant get any resistance reading even with my HP analog VTVM on the 1 M scale. This makes me think it has to be disconnected as I cant imagine it being that open. another test will be to send a voltage thru it and see if the VTVM can pick that up. I have found this useful when trying to read extremely high resistances. Clearly this high a resistance is not usable but I like to test things before disassembly in an attempt to collect data.

    doing all this before disassembly just in case its gets destroyed in the process of removal.

    Edited by Dave WM

    Share this post


    Link to post
    Share on other sites

    here you go. It seems like there is a meshed liner that acts as a filter for the gasoline that enters the chamber, then you can see the tiny disk shaped thermistor

    100_1986.JPG

    100_1987.JPG

    • Like 1

    Share this post


    Link to post
    Share on other sites

    it def was NPT I was able to hold the disk in between the ohm meter probs, got about 1.5k and it would drop when heated. I was not able to resolder the broken piece, I suspect it was a elec weld but not sure about that. Maybe a conductive epoxy. I cleaned it but was unable to get solder to stick. I suspect the material I was "cleaning" was some semi conductor as it sanded very easy leaving what looked like a metallic shiny surface. I am not sure what pure germanium looks like but maybe something like that.

    • Haha 1

    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

    ×
    ×
    • Create New...

    Important Information

    By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.