Perplexing "FUEL" light malfunction

[Zed Head]

23 minutes ago, Dave WM said:

its not a stock thermistor? oh well that could explain things.

It's "new".  I assume that the offending part is shown here.  Maybe it has numbers on it.  Just noticed that they put "copy of" in the url.  

https://zcardepot.com/products/copy-of-fuel-tank-gauge-sending-unit-sender-240z-260z-280z-70-78?_pos=3&_sid=b7ce84965&_ss=r

Edited July 24, 2020 by Zed Head

[Zed Head]

1 hour ago, SteveJ said:

The Fry's closest to me (about 3 miles from my office) was almost an empty warehouse the last time I visited. Are they back to stocking products?

I used to go the one in Wilsonville, by Portland.  It was well-stocked but it's been years.  Maybe they're dying too.

[dmorales-bello]

3 hours ago, Dave WM said:

you would prob want to get a WW pot, those cheap carbon track pots would not like the current. I think I have some 100 or 500 ohms ones laying around if you cant get the fix with the different bulbs.

That's a great offer, Dave. I will try to find as low a wattage bulb as possible and order it to finish off experimenting with the bulbs. If that fails I will gladly take your offer and purchase one of your potentiometers (whichever you think best suits the application) and attempt that remedy.

[dmorales-bello]

2 hours ago, Zed Head said:

It's "new".  I assume that the offending part is shown here.  Maybe it has numbers on it.  Just noticed that they put "copy of" in the url.  

https://zcardepot.com/products/copy-of-fuel-tank-gauge-sending-unit-sender-240z-260z-280z-70-78?_pos=3&_sid=b7ce84965&_ss=r

Here are are couple of pics of the Z Car Depot thermistor. It has no markings on it whatsoever. I must say that the whole sender unit seems to be a high quality reproduction. This thermistor issue is unfortunate.

BTW, the pics are from the first sender I received from them which is out of the car. When I notified them of the malfunction they immediately sent out another one which is currently installed in the tank. They are both identical.

[Zed Head]

If they're the same you have one to experiment on.  Results should translate.  Today's electronics manufacturing processes are all about process control to produce identical parts.  For that type of part you really shouldn't see a defect.  I wonder how many they have sold, and how many have actually been installed.  You might be the first.  p.s. I say they but I think it's just one guy.

I wonder if some of the delay is due to all of the metal surrounding it.  Might be fun to hook it up to a battery and see how warm it gets.

Edited July 24, 2020 by Zed Head

[dmorales-bello]

5 hours ago, SteveJ said:

If you want to experiment further, here is a site with different wattage bulbs: https://www.bulbtown.com/9mm_Diameter_Bayonet_Base_s/1421.htm

In looking at the available bulbs in your link I'm a bit lost because they all have different voltage ratings and none are 12 volt (like the one I'm replacing). I understand that I need to go below 3.4 watts but how about the voltage rating? Which bulbs would you suggest for the test?

[SteveJ]

6 minutes ago, dmorales-bello said:

In looking at the available bulbs in your link I'm a bit lost because they all have different voltage ratings and none are 12 volt (like the one I'm replacing). I understand that I need to go below 3.4 watts but how about the voltage rating? Which bulbs would you suggest for the test?

Automotive bulbs are rated for 14 VDC. (sometimes 14.4)

https://www.bulbtown.com/9428049_GM_General_Motors_Replacement_Bulb_p/9428049.htm

https://www.bulbtown.com/274020_GM_General_Motors_Replacement_Bulb_p/274020.htm

https://www.bulbtown.com/1813_Miniature_Bulb_Ba9S_Base_p/1813.htm

https://www.bulbtown.com/274004_GM_General_Motors_Replacement_Bulb_p/274004.htm

https://www.bulbtown.com/363_Miniature_Bulb_Ba9s_Base_p/b363.htm

There are probably others within that list. I didn't go down each page.

[dmorales-bello]

33 minutes ago, SteveJ said:

Automotive bulbs are rated for 14 VDC. (sometimes 14.4)

https://www.bulbtown.com/9428049_GM_General_Motors_Replacement_Bulb_p/9428049.htm

https://www.bulbtown.com/274020_GM_General_Motors_Replacement_Bulb_p/274020.htm

https://www.bulbtown.com/1813_Miniature_Bulb_Ba9S_Base_p/1813.htm

https://www.bulbtown.com/274004_GM_General_Motors_Replacement_Bulb_p/274004.htm

https://www.bulbtown.com/363_Miniature_Bulb_Ba9s_Base_p/b363.htm

There are probably others within that list. I didn't go down each page.

 

 

Thanks for the help. Just placed the order and should have six different bulbs to experiment with by middle of next week.

For each bulb I will first check to see if it illuminates with the connected sender OUT of the gas tank and the car key in the "ON" position. If any of the bulbs fail to illuminate, that one will be eliminated from further trial.

Next, with the sender installed in the tank with fuel, I will run the engine for 15, 20, and 30 minutes and see which bulb (if any) light up. 

Hopefully at least one of them will not and the problem should be solved. If not then it's pot time. (By that I mean "potentiometer", not weed. LOL)

[AZDatsun]

I have the same sender from zcardepot and my fuel light doesn’t light up but it never has... The fuel gauge does seem very accurate. Sorry I have added nothing helpful to this topic but I am following with interest. I replaced my bulbs with LEDs and still doesn’t work. I only got it because the last sender didn’t move my gauge needle properly and this fixed it.

 

 

Sent from my iPhone using Tapatalk

[dmorales-bello]

1 minute ago, AZDatsun said:

I have the same sender from zcardepot and my fuel light doesn’t light up but it never has... The fuel gauge does seem very accurate. Sorry I have added nothing helpful to this topic but I am following with interest. I replaced my bulbs with LEDs and still doesn’t work


Sent from my iPhone using Tapatalk

Did you try plugging in the unit before putting it in the tank with your key to the "ON" position? That should trigger the light in about 10 seconds or so.

BTW, what alternator are you running?

[ETI4K]

As an aside, does anyone know how current production vehicles trigger a low fuel warning?

Perhaps this is an area where a leap forward would be of value.

[Dave WM]

Turns out mine is not working, was working awhile ago. Spent the day trouble shooting. Back prob the connector at the center console. Key on fuel in tank disconnect the lamp and you should get 12v at the back prob (with out the load of the lamp you get the full battery voltage due to the high impedance of the DVM). Plug the light back in and the 12 drops down to about 20-30 millivolts (again back probing the connector from the lamp the harness that is under the dash). I next pull the sending unit. Tip remove the tank mount by the fuel pump but leave the tank in place. This will give you way more room to work around the sending unit ring (this is with the side mount sending units). Visual of the thermistor can shows a fine layer of corrosion where it snaps in. I remove the thermistor can clean both the can and the retaining clip with some fine sand paper, Try it again this time with the sending unit outside of tank. It works but not as well as I like plus I see some intermittent drops of the voltage while I monitor the back probes. down to zero... hmm must be a break in the circuit. I noticed the can has a small wire that comes out the bottom and is not firmly attached. I presume this is the electrical ground for the thermistor. I solder that to the can bottom. Much better action now. I am posting up a video will link here when  done.

 

Edited July 25, 2020 by Dave WM