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dmorales-bello

Perplexing "FUEL" light malfunction

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    roger, I have a 150 ohm WW pot think its 2 watt rated (it will get warm, so really just use to size the correct fixed resistor once the value is known) ready to send. Would like Capt O to confirm my value as a good starting point (any higher resistance I think would render the light dark not matter what the sender does). You would want to use some jumper wires (3) to insert in series with the connector plug that you back probed. 1 jumper is a direct pass thru, the other two connect the pot between the remaining plug lead. Start off with max resistance and see if the light stays off, if it does, then you can sneak up on the lower resistance until it just starts to light, back off and you should be good. Note the resistance value and substitute the pot for a 5 watt WW resistor. This all assume it actually works and you are not able to get it to work with the other bulbs.
    incase it was not already covered regarding bulb experiments:
    On the other bulbs, remove the current installed one, check the resistance , then check the replacements. pick the one that has the highest resistance. We are trying to limit the current to keep the thermistor from self heating beyond what the fuel cooling can dissipate. install the highest resistance bulb and try again. This is the same as adding the pot in series and adding resistance with it.
    Got it. Thanks again.
    I hope CO can confirm values.

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    I got data.

    I applied voltage to a FUEL warning lamp indicator (red lens and all) and "analyzed" the brightness. I came up with the highly subjective brightness levels of:

    Barely noticeable
    Clearly noticeable
    ON
    Attention getting
    Angry

    I measured these values in both a "poorly lit room" and a "well lit room", and here's what I got. It's neat (geekwise) that you can clearly see the filament resistance increasing as the current (and temperature) goes up:

    fuellamp2.jpg

    It appears that what you really want is for the thermistor to work the way it's supposed to. Failing that, I would try maybe a 50 Ohm pot in series and see what happens? I'll leave it to Dave to calculate the power dissipation in the pot and determine if it's feasible.  LOL  

    Edited by Captain Obvious
    typo

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    roger that, so any more than 50ohms added it a waste of time as it will keep the light from functioning. I have my doubts about the feasibility of the pot fixing the issue, seems as you say it really needs to work as it is supposed to (correct specs on thermistor), but short of that I have a 50 ohm WW pot ready to go to Dr. Dave. He is messing with some other bulbs now. I think I will get a cold filament resistance reading of my car and report back.

    lamp at leads that plug into wire harness resistance 6.0 ohms

    Edited by Dave WM

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    20 minutes ago, Dave WM said:

    lamp at leads that plug into wire harness resistance 6.0 ohms

    Yup. I measured mine at approx. 5.4 cold.

    Maybe yours is a couple hundred milli-Ohms higher because you're in hot sunny FLA.   LOL

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    I am posting up a video, will link here, showing my hookup and how it effect brightness of the lamp. I can control the horz I can control the vertical, ….

    ok CO what show is it...

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    I received 5 bulbs with different ratings yesterday. They do not show the Volt or Amp rating on them as other bulbs do. Therefore I decided to identify them by the measuring each bulb's resistance on the bench (cold resistance?).
    Once again I ran the car with the original 12V 3.4 amp bulb in the "fuel" light housing with the tank at about half full. Once again that bulb lit brightly after about 25 minutes. With the car still running I swapped the stock bulb for each one of the new bulbs. All of them illuminated immediately although dimly. The difference lies in how dimly each one lit up. In general, the bulbs with the highest cold resistance were dimmest. I was also measuring voltage at the bulb harness for each bulb. That voltage varied when each new bulb was placed in the socket but stabilized within a minute or less. I identified the bulbs from #1 to #6 in order of decreasing resistance. Bulb 1 being the new bulb with the highest resistance and bulb 6 being the stock bulb which had the lowest resistance.
    RESULTS :
    BULB 1: 19.8 Ohms, weakest glow, stable at 2.9 V.
    BULB 2: 12.7 Ohms, weak glow, stable at 3.1 V.
    BULB 3: 11.5 Ohms, very weak glow, stable at 4.0 V.
    BULB 4: 11.4 Ohms, slightly brighter glow, stable at 3.3 V.
    BULB 5: 6.3 Ohms, brighter glow, stable at 5.8 V.
    BULB 6: 3.8 Ohms, very bright, stable at 7.7 V.

    The glow from bulbs 1, 2 and 3 can barely be seen through the red lens of the housing even inside the darkened cockpit (I was outside at 9pm. Wife thinks I'm going insane! LOL). With the roof light on, you can't detect light through the lens.

    The glow from bulbs 4 and 5 can be readily seen through the red lens in the dark (5 more than 4) and are somewhat visible with the roof light on.

    Bulb 6 (stock) is very blatantly visible in the dark and quite bright with the roof light on.

    I ruled out the stock bulb (6) , and the new bulbs at each extreme (1 and 5) for being too dim or too bright.
    Bulbs 2, 3 and 4 are dim enough that are very hard to be seen through the lens, day or night. But should be brighter and visible when the thermistor is above fuel and it's resistance drops (I think).
    I placed bulb 3 in the housing and closed everything up. I will run the tank dry and see how the light behaves. I will have bulb 2 and 4 as alternatives.

    I know my "report" is not very technically correct but it kinda gives me options.


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    Thanks for the video once again, Dave. I would think the pot could be used with the lower resistance bulbs. If I were to use it with the higher resistance bulbs they would probably never light up even with the thermistor out of the gas, correct?

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    you may want to use the dimmest bulb and just see if it works as designed when you run low, of better still, if yours it a top loader, I would say just pull it up until you can see the thermistor is not submerged, the see if it works, it should come on brighter in a few minutes. That way you will at least know the system is seeing the change in submerged vs not submerged.

    From there you can determine the max brightness to determine if you can live with the bulb #1

    Maybe you can say that the dim always on is a way to confirm the system is active if the rest of it works as it should. This is actually a good idea if the dim light is not annoying.

    (see "andromeda stain" paper in bell clapper reference for Capt O)

     

     

    Edited by Dave WM

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    36 minutes ago, dmorales-bello said:

    Thanks for the video once again, Dave. I would think the pot could be used with the lower resistance bulbs. If I were to use it with the higher resistance bulbs they would probably never light up even with the thermistor out of the gas, correct?

    Sent from my SM-N950U using Tapatalk
     

     Since its adjustable from 0-100 you can use it with any of the bulbs actually just depends on how much resistance you add, less with the high resistance bulb, more with the low resistance bulb.

    you just need to adjust the setting to what works. the bulb and the thermistor both vary resistance with heat, the pot is the only thing that once set does not vary.

    The pot is just a work around for a system that can not stabilize in to a low current steady state while submerged. There is something fundamentally wrong as is, but at this point its got to be either the performance of the thermistor OR for some reason the gas is not cooling the thermistor as designed. The bulb is the only other variable and with the selection you have to choose from that should not be an issue.

    Edited by Dave WM
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    On ‎7‎/‎30‎/‎2020 at 9:28 AM, Dave WM said:

    I can control the horz I can control the vertical

    Well that one is easy but you're sure pulling out the stops with the Andromeda Strain reference!! That was a fantastic movie. I saw that movie many moons ago (waves arm), and it scared the craps out of me. And to be honest, I remembered the basic plot and story, but I didn't remember the details of the bell clapper on the teletype. I had to go look that one up!  :beer:

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    So Dr. Dave,

    Can we drop back one last time... Is there any possible way your thermistor is NOT dunked in gasoline at half tank when the light comes on?

    I know you verified that the holes allow liquid to enter the sensor. Is there any possibility that the location of the holes is important? Stagnation perhaps?

    Does your old thermistor on your original fuel sender unit still work? If so, any thoughts on swapping the two and getting on with life? Want to send me some parts and I'll see what I can do with them?

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    10 hours ago, Dave WM said:

    this use of movies subplosts to communicate reminds me darmok

    Dr. Dave using stone knives and bearskins.    LOL

    • Haha 1

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    So Dr. Dave,
    Can we drop back one last time... Is there any possible way your thermistor is NOT dunked in gasoline at half tank when the light comes on?
    I know you verified that the holes allow liquid to enter the sensor. Is there any possibility that the location of the holes is important? Stagnation perhaps?
    Does your old thermistor on your original fuel sender unit still work? If so, any thoughts on swapping the two and getting on with life? Want to send me some parts and I'll see what I can do with them?
    Good morning CO! I actually measured the distance from the edge of the tank where the fuel sender fitting is to the fuel surface at half tank (5"). The thermistor is 10" from the sender base so it must be sitting 5" beneath the fuel surface at half tank.
    The holes in the ZC Depot thermistor are smaller than those on my original unit. Perhaps they would allow trapped air to escape and fuel to flow in easier if they were twice the diameter (more similar to stock). However, when I ran the bench tests it seemed like water flowed in and out unrestricted.
    My original thermistor does not work (registers no resistance) and I would have no problem sending it to you for post mortem study.

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    7 minutes ago, dmorales-bello said:

    2000 BC?

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    city on the edge of tomorrow (oops forever)..like the use of vacuum tubes..

    an accident with a mechanical rice picker....

     

    CO and I spent WAY too much time in front of the idiot box.

    Edited by Dave WM
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    reminds me of the old joke

    Comedians get together every year for a convention. after years of telling and retelling  the same old jokes they start numbering them for convivence.

    guy gets up on the stage... says into the microphone #26... a few giggles....#104....some more....then #62... uproar!!! a guy in the crowd says, "man that was a good one" guy next to him says yea, but what about the great timing....

     

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    city on the edge of tomorrow (oops forever)..like the use of vacuum tubes..
    an accident with a mechanical rice picker....
     
    CO and I spent WAY too much time in front of the idiot box.
    I guess I go way back before you guys! LOL. I was thinking of making a bear skin outfit for Raquel Welch in 2000 BC. My mind keeps going back to cutting and sewing, I suppose.

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     I think it needs a hole in the top to allow ALL the air to escape.
    It has a smallish slit on the top but I think a larger escape hole for the air would benefit the design. One could always drill an additional 1/16 hole with a hand mandril very gently into the white plastic cap on the top. I think Dave WM took one apart. Would it be safe to drill through the plastic cap?

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    2 hours ago, dmorales-bello said:

    I guess I go way back before you guys! LOL. I was thinking of making a bear skin outfit for Raquel Welch in 2000 BC. My mind keeps going back to cutting and sewing, I suppose.

    Sent from my SM-N950U using Tapatalk
     

    Miss fuzzy britches..

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    Dave. Dave!    LOL   Come back!!   Dr. Dave asked you a question:

    10 hours ago, dmorales-bello said:

     I think Dave WM took one apart. Would it be safe to drill through the plastic cap?

    Haha!!

    So Dr. Dave, I don't think there would be a lot to be learned from a post mortem on the dead one. The only really interesting thing would be to characterize the thermistor against a temperature curve, but if it's open circuit, that won't be possible. I guess there's a tiny but non-zero possibility that the open circuit break is somewhere I could see and kluge together long enough to take some measurements. There is also a tiny, but non-zero possibility that there might be a part number on the outside of the sensor?

    Up to you if you want to waste the dollar it would cost to mail it.

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