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dmorales-bello

Perplexing "FUEL" light malfunction

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Couple days ago I picked up a spare fuel sending unit to mess around with. First thing I did was checked the thermistor, and it's open circuit. So unfortunately no help there with analyzing a working one, but at least I get to see the thing with my own two eyes.

So since the thermistor was already dead, I figured no harm in starting the autopsy. Desoldered the end lead:
P1170416.JPG

And pulled (what's left of) the thermistor out of the can. The thermistor nugget itself is completely vaporized. Just like what you guys found, all that was left was the two leads:
P1170417.JPG

I still contend that there is nothing interesting inside the black plastic end plug. Here's some shots of the two ends:
P1170420.JPG

P1170421.JPGA

And for confirmation, I took it apart. It's just a brass ferrule with flared over ends so it stays in place inside the black plastic cap. And then they use that brass tube as a connection point to solder the flexible wire to one of the thermistor leads. Looks like this. They just bent the ends of the two wires into "U" shapes and hooked them together and then soldered the whole thing together:
P1170422.JPG

Here's the hollow brass tube after the solder has been removed:
P1170423.JPG

So there's no mystery hidden inside that plastic cap. It's just transition from yellow lead wire to the thermistor lead. @Dave WM If you're going to do another thermistor swap, you don't have to splice the wire to the old stub. You can just solder it into the ferrule.

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19 minutes ago, Captain Obvious said:

Couple days ago I picked up a spare fuel sending unit to mess around with. First thing I did was checked the thermistor, and it's open circuit. So unfortunately no help there with analyzing a working one, but at least I get to see the thing with my own two eyes.

So since the thermistor was already dead, I figured no harm in starting the autopsy. Desoldered the end lead:
P1170416.JPG

And pulled (what's left of) the thermistor out of the can. The thermistor nugget itself is completely vaporized. Just like what you guys found, all that was left was the two leads:
P1170417.JPG

I still contend that there is nothing interesting inside the black plastic end plug. Here's some shots of the two ends:
P1170420.JPG

P1170421.JPGA

And for confirmation, I took it apart. It's just a brass ferrule with flared over ends so it stays in place inside the black plastic cap. And then they use that brass tube as a connection point to solder the flexible wire to one of the thermistor leads. Looks like this. They just bent the ends of the two wires into "U" shapes and hooked them together and then soldered the whole thing together:
P1170422.JPG

Here's the hollow brass tube after the solder has been removed:
P1170423.JPG

So there's no mystery hidden inside that plastic cap. It's just transition from yellow lead wire to the thermistor lead. @Dave WM If you're going to do another thermistor swap, you don't have to splice the wire to the old stub. You can just solder it into the ferrule.

good to know thx Capt O!

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Update: I received a replacement fuel sending unit after my first one from zcardept started to engage the fuel warning light when the tank wasn't low on fuel.  After a few weeks of driving with the new sending unit, this new one started lighting the warning light even on a full tank.

I'm not sure what the issue is with the thermister on these, but it just seems to be a design flaw.

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An inline potentiometer would probably make it work right.  If you decide to keep it.  Crank up the resistance until the light is filament is barely visible in the dark, as described earlier, and it should brighten up when the thermistor gets exposed.

p.s. pretty sure ZCD was notified early in this thread but it's looking like they committed to this set of parts and are just going to keep selling them.  Like buying reman alternators at the local parts store.  Just keep returning it.  Too bad.

@zcardepot.com

p.s. #2 - if I understand all that's been desc (dang it just lost my cursor while typing) ribed in this thread then ZCD should be able to cut the line to the themistor, install a r (lost the cursor again) esistor and make it work right.  It will t (lost it again, with a new ad at the bottom) ake some rework but at least they can keep their investment in parts.

Edited by Zed Head

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I wrote ZCD a couple of weeks ago and described the issue along with our conclusions (after so much friggin work!), and the "easy fix" of using a different resistance bulb. They thanked me for being so thorough, that my email would be forwarded to the "boss", but they had sold many sending units without any issues. They left it at that, regrettably.

 

Sent from my SM-N950U using Tapatalk

 

 

 

 

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Just now, dmorales-bello said:

I wrote ZCD a couple of weeks ago and described the issue, or conclusions (after so much friggin work!), and the "easy fix" of using a different resistance bulb. They thanked me for being so thorough, that my email would be forwarded to the "boss", but they had sold many sending units without any issues. They left it at that, regrettably.

Sent from my SM-N950U using Tapatalk
 

Right, they told me the same thing before they sent a replacement.  😕

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This is one of those critical moments in running a business.  Do you take a relatively small loss, to keep your customers happy and your reputation in good standing.  Or do you hold your ground to save that small cost of fixing the problem, destroying the good will that exists and damaging future sales.  California Datsun comes to mind.  I hope these guys can handle the broad view.  They have a huge selection of parts now, the business has grown quite a bit since it first appeared, not that long ago.

This thread is like a case study in a business course.  What not to do.  Let's see what happens next...

https://zcardepot.com/

Edited by Zed Head
gerund is not ground
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