On my bike the low fuel light does not work when the fuel get low.It lights up when pushing the starter switch so its not the bulb.
I first tried to replace the wiring and connectors from the fuel level sender.That did not help.You can read abut that in this tread:
https://www.fjowners.com/index.php?topic=20119.0 (https://www.fjowners.com/index.php?topic=20119.0)
Anyway found the problem and it is a little strange thing called thermistor that is the bug.After a little research if found out that a thermistor works by
resistance not letting current flow thru it when it is at a specific temperature hot or cold. There is 2 types NTC is for negative temperature control and
PTC is for positive temperature control. The fj uses a NTC type .It sits inside the gastank and is constantly powered with 12 Volt when cooled by the fuel it
stops current flow so the fuel light not lights up.When fuel level gets low it is no longer immersed into the fuel and then it is able to heat up and the
current flows to the low fuel bulb.So here is a little writeup on how i replaced the thermistor in my bike.I have to place a WARNING if you plan to do this
job That is that I'm not a professional and did this work on my own risk.So do it on your own risk i think this may be dangerous if using wrong thermistor i
don't know if i have used the right thermistor and it does not look the same as the oem one that was in the gastank.
Here is a link to a youtube video that explain better how a thermistor works https://www.youtube.com/watch?v=UEmbRJKlSeI (https://www.youtube.com/watch?v=UEmbRJKlSeI)
I applaud your insistence on having a working low fuel light! My lazy ass would just use the tripometer.
Awesome job and write up! These type repairs will probably become more and more common as the components on these bike show their age more than the bike itself!
Like motofun said above - "little" things like this will be the difference of keeping an old FJ "running" vs one that is still a fully functioning example like it came new ... not that I'll ever be in danger of that myself!! :lol:
Old rider,
Inventive work, but it may not be safe over time. I strongly suggest that you replace the fuel sender with correct parts, even a used fuel sender.
The risks here are not worth the rewards.
Soldering can be easy and fun, but not with dirty tips, wrong Wattage soldering irons, poor solder, and bad fluxes.
Make a hole in a common sponge. Cut the sponge to fit in a flat jar. Wet the sponge with water. Cap the jar, when finished work.
Rosin flux is lame. Acid flux destroys wires. Use LA-CO paste flux (non-acid, washes away with water). Do not leave any flux on finished work, not ever.
Clean the soldering tip, bright and shiny, in the sponge. Add fresh solder to the tip. Clean the tip again, after every minute working.
Use temperature-controlled soldering irons. 50 to 100 Watt soldering irons will do most small-sized work.
A soldering iron running too hot gets too dirty, too fast. The wet sponge can clean and cool the too-hot soldering iron, but you will need to clean the tip very often.
A too-small soldering iron will not get the work hot enough to take solder well.
When finished, the solder should look smooth and shiny, like silver.
Quote from: Motofun on October 18, 2021, 07:29:45 AM
I applaud your insistence on having a working low fuel light! My lazy ass would just use the tripometer.
I use the tripmeter all time and know that my bike goes around 170 km on 10 litres .But i like that all bulbs are working on my bike :yes:
Quote from: fj1289 on October 18, 2021, 08:54:30 AM
Awesome job and write up! These type repairs will probably become more and more common as the components on these bike show their age more than the bike itself!
Like motofun said above - "little" things like this will be the difference of keeping an old FJ "running" vs one that is still a fully functioning example like it came new ... not that I'll ever be in danger of that myself!! :lol:
Thanks that is true about the old components i will be the testpilot to se how it goes but im now confident that this repair is safe after some more testing :yes:
Quote from: red on October 18, 2021, 09:46:41 AM
Old rider,
Inventive work, but it may not be safe over time. I strongly suggest that you replace the fuel sender with correct parts, even a used fuel sender.
The risks here are not worth the rewards.
Soldering can be easy and fun, but not with dirty tips, wrong Wattage soldering irons, poor solder, and bad fluxes.
Make a hole in a common sponge. Cut the sponge to fit in a flat jar. Wet the sponge with water. Cap the jar, when finished work.
Rosin flux is lame. Acid flux destroys wires. Use LA-CO paste flux (non-acid, washes away with water). Do not leave any flux on finished work, not ever.
Clean the soldering tip, bright and shiny, in the sponge. Add fresh solder to the tip. Clean the tip again, after every minute working.
Use temperature-controlled soldering irons. 50 to 100 Watt soldering irons will do most small-sized work.
A soldering iron running too hot gets too dirty, too fast. The wet sponge can clean and cool the too-hot soldering iron, but you will need to clean the tip very often.
A too-small soldering iron will not get the work hot enough to take solder well.
When finished, the solder should look smooth and shiny, like silver.
Thanks for you advice Red ,but i have seen others done the same repair.They have used 1k thermistor as i did.I have now done some more testing how
hot it gets and what happens if shorting the wires on it, but that is very unlikely.I now feel confident that nothing bad can happend
about the soldering
Thanks for the soldering advices i have the solderingstation on the pic it is almost first time soldering and did much of what you have sayd ,but
my soldering iron now looks like something from first world war and it is impossible to get the solder to stick to it i think i got the wrong flux too
it is called "lodenwasser" solder water
Since i did not manage to measure the temps on the thermistors with a ir thermometer last time.I got a better thermometer and re-measured.
It is more accurate i think and it goes up to 300 degree celsius.I think the thermistors gets hotter than this thermometer reads but not much
mayby 10-20 degree more than measured value.I wanted to be sure that the temp stay under 250-280 degre that is gasoline ignition temp.
The hottest temp that was measured was 89 degree but it is probably a little more so i feel that the repair is safe.Nothing happened on the
2 days about 100km of riding with low fuel.I dont know what resistance the oem thermistor in a fj has ,but it is normal on other bikes to have
a 1K NTC installed same as i have done.
Maybe someone with a working fuel light can measure with multimeter to see what resistance the oem thermistor is .measure on the wires at the connectorplug it is 3 wires there.unplug the connector and measure on the black and on the grenbrown
wires. set multimeter at ohm
Thermistors change resistance with temperature. To compare them you must measure the resistance of each thermistor at the same temperature. There is also a temperature curve which is how much the resistance changes as the temperature changes so the resistance should be measured and compared at different temperatures to see if the curves are similar.Devices I work on that use thermistors usually provide a temperature vs resistance curve chart. Since you are only turning a light on and off it probably has some leeway.
Quote from: Old Rider on October 19, 2021, 08:32:38 AMabout the soldering
Thanks for the soldering advices i have the solderingstation on the pic it is almost first time soldering and did much of what you have sayd ,but
my soldering iron now looks like something from first world war and it is impossible to get the solder to stick to it i think i got the wrong flux too
it is called "lodenwasser" solder water
Old Rider,
Soldering irons are really pure copper, most often. Some soldering tools have replaceable tips. Contact the company who makes the tool, if possible, for new tips. Otherwise, you can refurbish the end of the iron. First, use a soft fine-wire brush to clean away the crusty flakes. Use a flat file to shape the copper into a blunt common screwdriver shape, or shape it like a large common nail, with three flat surfaces at the tip
/\. With only bright shiny copper showing, wrap the tip copper tightly with solder-wire, so the solder-wire looks like a tight coil spring on the tip. Add flux, and turn on the iron at a low setting, hot enough to melt the solder on the tip, but not extremely hot. When the solder melts, wipe the tip clean in the damp sponge. That process should give you a good working tool.
New solder tips may be coated (plated) with soft iron. I like to preserve the iron plating which you may get on some new tips, so a soft wire brush starts the tip cleaning. That brush may be enough to get the iron clean, and ready to be tinned with solder again. Once the plating gets hopelessly corroded, however, you will have to file down the end of the tip (when cold) to see the clean copper. All soldering tools were bare copper a few decades ago, so do not be concerned about any iron plating lost to the file. The tool will work well, with or without the iron plating.
A local plumbing supply house should have several good fluxes available; rosin is a minimally capable flux, and acid flux is
not for electrical work. I suggest LA-CO flux (or similar), if possible.
https://markal.com/collections/soldering-fluxes/products/regular-flux-paste?variant=9204786921519 (https://markal.com/collections/soldering-fluxes/products/regular-flux-paste?variant=9204786921519)
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Quote from: T Legg on October 19, 2021, 11:30:08 AM
Thermistors change resistance with temperature. To compare them you must measure the resistance of each thermistor at the same temperature. There is also a temperature curve which is how much the resistance changes as the temperature changes so the resistance should be measured and compared at different temperatures to see if the curves are similar.Devices I work on that use thermistors usually provide a temperature vs resistance curve chart. Since you are only turning a light on and off it probably has some leeway.
Thanks for that info .The thermistors i have has a range from 25 to 150 degree it was 17 in the room and i noticed that when the thermometer raised to 25 the bulb started glowing.
When i did the testrides it was only about 4-8 degree outside i then had filled 4 liter before the ride and the bulb started to glow anyway ,but that is maybe because it was heated from the current .When at gas station filled 4 liter again the bulb shut of and started to light up faint again after riding 50 kilometer but by then the heat from engine must have heated the fuel in tank
wonder how it is in hot summer temps cant check that before next summer as the first snow fall came tonight
Red : Thanks for many good hints to save the solderiron i will try them out .The label on the flux i got says it is acid so now i know that was no go :good:
Here in the US there is a goofy TV commercial for a mortgage company selling home equity loans.
The commercial shows a guy driving a crane with a wreaking ball, towards his house. He said to his neighbors who are watching, that he is going to find the "hidden money" in his home.
The neighbor wife said to her husband, "Should we tell him about home equity loans?"
The husband replies, "No, let's just see where this goes..."
I'm with Red on this one....but still.....I can't seem to look away.
Please be Uber careful...I really appreciate your documentation. Really.
He he i could always put in a 3w bulb or less that will keep the thermistor cooler ,but i think the temp on it is safe.
I will report how it goes but so far no problems. :biggrin:
King winter now starting to arrive so i have now wrapped the bike in for hibernation.The testrides showed that the fuel light worked as it should,but
when riding i also taught about the test i did earlier with water when the bulb did not shut off. It could be that i installed the thermistor not careful
enough and one of the wires got too close the metal inside the canister making a short.i have to replace the sender gasket anyway so i decided to check
the thermistor some more.After inspecting it more i found that one of the wires on the thermistor was very close to the metal wall inside and need to be
fixed.
After reading a little in the docs i linked to about explosions in gas tanks the repair now feels very safe.
https://www.nrel.gov/docs/fy09osti/44040.pdf (https://www.nrel.gov/docs/fy09osti/44040.pdf)
https://www.nrel.gov/docs/fy10osti/47819.pdf (https://www.nrel.gov/docs/fy10osti/47819.pdf)
https://www.nrel.gov/docs/fy11osti/52043.pdf (https://www.nrel.gov/docs/fy11osti/52043.pdf)
Old rider, I see you had the same issue with your fuel light sensor. I have had issues with mine as well. I see this is from October of last year but thought this might be worth mentioning anyway. I ordered up the Thermistor unit (the case with the Thermistor inside) on eBay here in the US. It is for a Datsun 280ZX Thermistor Low Fuel Warning SENSOR Replacement. It looks to be exactly the same size and specs as the FJ1200. If you do have any issues with your fix you may want to locate one. I have not received it yet but I think it will do the trick unless there is something I missed.
Thanks for the tip Wayne, please report back when you get the unit and let us know how it works out.
Cheers
Quote from: wco56 on January 20, 2022, 12:10:05 PM
Old rider, I see you had the same issue with your fuel light sensor. I have had issues with mine as well. I see this is from October of last year but thought this might be worth mentioning anyway. I ordered up the Thermistor unit (the case with the Thermistor inside) on eBay here in the US. It is for a Datsun 280ZX Thermistor Low Fuel Warning SENSOR Replacement. It looks to be exactly the same size and specs as the FJ1200. If you do have any issues with your fix you may want to locate one. I have not received it yet but I think it will do the trick unless there is something I missed.
Hi Wayne i also found that on eBay also found another one that has 2 wires on it. I posted 2 pics of how they look .The canister has to be welded/soldered on the fuel level sender holder arm and the wire soldered in the sender or spliced so it is a little work involved with that too.
Mine works fine ,but i did some more searching for a thermistor that was straight so you don't have to bend the wire inside the canister and i did find one see the pic
below. I ordered it to see if that was a better option than the thermistor i installed ,but that ended up beeing a funny story.
I pulled the sender unit out and had everything waiting to go when the new thermistor arrived (see attached photo). The size was exactly the same as the old part and the install was very straightforward. I did have to solder the casing into the wire mount, which was simple enough. I also cut the thermistor wire to length and soldered it in place to complete the circuit. I would say the only thing to be aware of is when you solder the wire inside the housing be sure the slack in the wire does not interfere with the sweep on the sender itself. Sorry but I was remiss in not taking photos of the new thermistor in place. I bench tested the sender unit and the thermistor to be sure it was operational and I installed with a new rubber gasket to seal it in the tank. It works fine and it doesn't get much easier than that from my perspective. I will say that when I bought the thermistor on eBay I paid $5.00 USD. After I bought mine I see the seller is asking $30.00 USD now. At $5 I got a true bargain, but at $30 I would consider Old Rider the fiscal winner, and I would seriously consider doing the extra work to make the fix.
Quote from: wco56 on January 29, 2022, 09:20:22 AM
I pulled the sender unit out and had everything waiting to go when the new thermistor arrived (see attached photo). The size was exactly the same as the old part and the install was very straightforward. I did have to solder the casing into the wire mount, which was simple enough. I also cut the thermistor wire to length and soldered it in place to complete the circuit. I would say the only thing to be aware of is when you solder the wire inside the housing be sure the slack in the wire does not interfere with the sweep on the sender itself. Sorry but I was remiss in not taking photos of the new thermistor in place. I bench tested the sender unit and the thermistor to be sure it was operational and I installed with a new rubber gasket to seal it in the tank. It works fine and it doesn't get much easier than that from my perspective. I will say that when I bought the thermistor on eBay I paid $5.00 USD. After I bought mine I see the seller is asking $30.00 USD now. At $5 I got a true bargain, but at $30 I would consider Old Rider the fiscal winner, and I would seriously consider doing the extra work to make the fix.
Great work! I'm very curious about what type thermistor is mounted inside .Is it the original yamaha shape or maybe it is the same type i have mounted a bead with 2 wires coming out from one side. Did you try to take a look inside the canister and did you measure the ohm resistance ?
Sorry, but I never opened the canister up. I didn't want to take a chance on causing damage. I didn't take readings on the resistance but I did check resistance to see if it changed when heat was applied to the canister. Everything checked out good and I installed it. I figured I will give it a real world test when spring arrives here in New York State, but that will be a couple of months from now.
Hello some of you might think (or hoping) i was dead from a gastankeksplosion ,but im not! im alive so far :good2: I have now added a fuse and a weaker bulb to make
things more on the safe side .Since im not a expert on electronics im not sure if the fuse will do anything =) But a weaker bulb will atleast make the thermistor run cooler that i have tested.
Quote from: Old Rider on April 17, 2022, 02:25:25 PMHello some of you might think (or hoping) i was dead from a gastankeksplosion ,but im not! im alive so far :good2: I have now added a fuse and a weaker bulb to make things more on the safe side .Since im not a expert on electronics im not sure if the fuse will do anything =) But a weaker bulb will atleast make the thermistor run cooler that i have tested.
Old Rider,
Just a suggestion, but if you have another thermistor handy, you might want to keep what you have going there. As a separate experiment, try using an LED bulb instead of an incandescent bulb. They are more Off/On, and need much less power than a normal bulb. You may need a resistor in line to reduce current flow into the LED bulb, but the LED should be brighter in-flight.
Hi Red. I have tested with a LED bulb i wrote about it in my first post .If using a LED bulb it will pop on and off too fast so i think that the bulb will light up even if there is alot of fuel in the tank when turning left or accelerating and fuel is splashing around.I will flicker.With the normal iridescent bulb it takes about 10-15 seconds for the bulb to start to glow and it light up first weak when fuel getting lower and stronger and stronger as fuel level sinks.