mack123

iTrader: (4)

Hello all,

I had some free time last week so I decided to repair my inop low fuel light on my
88 turbo.
I ran a jumper from the low fuel connection on the plug by the pump, and the light
came on, so I knew the in tank sensor or wire connections were bad.

When I got the fuel pump out the sensor is a little silver/aluminum can, about the
size of a finger end. One wire runs from it, it is a clear coated copper wire, which ends
at a terminal on the base of the fuel sending unit.
I cleaned all the wire connections nice and shiny, reinstalled it, and no luck.
The sensor is bad.

So I gave the sensor a good looking over, and heer is what I gathered.
Feel free to correct me if wrong...

Inside the little sensor can is a thermistor.
A temperature activated resistor of sorts that provides continuity at a warm temperature.
When the tank is full, the thermistor is totally immersed in gas, and this cools
the thermistor, so it acts as an open, providing no continuity.
Then, when the gas level drops, gass drains out of the can, it has 3 holes in the top,
3 holes in the bottom.

The can is soldered to a metal arm, which goes back to the tiny cover of the fuel level unit.
This is the pathway to ground, when the sensor warms up and provides continuity.
So this gives a ground to the low fuel light, in the warning cluster. Very simple.
When it works, ha.

On one end of the sensor can is a soldered end. This holds the wire in place on the bottom.
If you pull from the top, it will break the thermistor in half.
So I unsoldered the end, and widened the other rubber/cork end, and the wire assembly slipped out.
Then I saw why the sensor didnt work.
The thermistor in the middle was seperated, brittle, and broke.
It looks to be a charcoal type piece, and I can see how years of service would bring these tiny thermistors to ruin.
There is no repairing the thermistor, I need a new one.

So, I spent a lot of time online tracking them down.
Here it is....

Panasonic # ertlg12n5, a direct replacement, can and all.
So I contacted about 7-8 panasonic electrical dealers.
They ALL wrote me back and said the same thing...
" These parts are discontinued and not available. "
Im not one to give up, so I followed up with a request for just the specific thermistor,
since I could easily resolder one in.
I have recieved no answer. When I checked one company, it said they had 2,400 sizes, doh.

Does anyone know the part number for this thermistor ?
If so, it is the golden ticket to repairing my low fuel light...
And I know many other forum members would be grateful also.

I did find another way to buy the cans, many motorcycles use the same sensor,
they have low miles and would be an alternative.
However a thermistor is like 1.00, and I would prefer a nice strong new one
inside that little can.

I will post a pic/info of the data sheet for the ertlg12n5 specs....
and if there any electrical experts out there who would know a right sized thermistor for this application ?? ... please chime in...
Thanks

mack123

iTrader: (4)

this might help with some more info....

http://industrial.panasonic.com/www-...AUD0000CE2.pdf

mack123

iTrader: (4)

hey Pele or Hailers, you guys around ? I know you could figure this one out...

mack123

iTrader: (4)

anyone know what size thermistors ?
there are many rx-7 owners on here who have a non working low fuel light.
This info could really make a change for our cars, for the better.

J-Rat

iTrader: (2)

Looks like you are pretty much on the right track.. have you considered other vehicles and adapting their sensors? Might get lucky with a newer car not having a discontinued thermistor.

mack123

iTrader: (4)

Thanks J-Rat, good info.
Actually I did find out that nissan maximas and the older mazda 626's have the same sensor,
however the donor cars I found at the junkyard all needed the gas tank dropped to get to it.

I found one from a late model motorcycle, which I can connect/solder the copper wires and
all will be good.

Panasonic, which claims on its websites to have superior customer and technical support on all its electronics, did little to nothing to follow up on a simple question they have in all their books.
Sooner or later everyones low fuel lights will be inop and hopefully another vendor will step in.
Thanks again.

Pele

iTrader: (28)

Thermistors all carry a temp to ohms curve... Find the spec sheet for this thermistor and find a similar unit from another manufacturer...

mack123

iTrader: (4)

The specs sheet link is listed above. Panasonic claims this is the only one they have since it is now discontinued. They also list 2,400 thermistor types, sizes, etc, and I narrowed it down to about 20, however I wanted to be exact. I dont want the sensor coming on at half a tank, ha.
I did find only 1 more maker, and these are used on yamaha motorcyles.
The sensor is listed with this maker, however it is a 'custom packaged order' meaning they size the connecting wire etc, for a direct application, with a minimum order of 10,000 no doubt, ha.
I might do a test when my sensor arrives and find out the exact temp/omhs when it has continuity. Then I would know the exact specs.
Thanks for the input.

brent_strong

iTrader: (2)

Reviving a dead thread, but I've hopefully found a solution for this that doesn't involve spending $100+ on a new fuel level sensor unit just because the "low fuel light" stays on.

I found this thread:
[AEU86] EU AE86 community :: View topic - How to: Repair low fuel warning sender

I'm going to buy a few of these:
RL2004-582-97-D1 GE M&C / Thermometrics | Mouser

Then it should be a relatively easy job to follow the writeup in the thread and replace the thermistor. $1 part, $5 shipping, a couple hours of work...and hopefully it will fix the light!

misterstyx69

iTrader: (142)

/\ that first thread is Real good info!
Thanks for sharing.

brent_strong

iTrader: (2)

No problem! I picked up a pretty good condition '87 Turbo from a friend as a project. The first order of business for me is to get all (or at least most) of the electronics functioning properly...including the stupid ones like the low fuel and washer fluid idiot lights.

When I tear into the sensor, I'll be sure to take some pictures and do a writeup. It should be 100% identical to the thread I posted, but there might be some RX-7 specific tricks...

7speed

I'll be following this closely. For whatever reason I find it important to have this working as well. Document your findings thoroughly and hopefully it'll be archived. Good luck!

brent_strong

iTrader: (2)

Well, I got the thermistors from Mauser tonight, followed the instructions in the link, and now I have a perfectly working low fuel light!

The steps were essentially the same on the RX-7 as on the AE86 writeup. My car is an '87 TII. I think the S5 cars had a slightly different fuel pump assembly, but if it uses the same low fuel sensor, these instructions will work fine.

I didn't think to take any pictures until it was too late. I have two leftover thermistors though, so I guess if someone wants me to repair a low fuel sensor for them, I can do it and get photos this time. Or just reference the pictures in this thread:

[AEU86] EU AE86 community :: View topic - How to: Repair low fuel warning sender

Part source:
Ordered 3 of these at ~$1 each and $5 shipping.
RL2004-582-97-D1 GE M&C / Thermometrics | Mouser

Tools needed:
Screwdriver, pliers, 6mm(?) socket/wrench for fuel pump removal
Soldering iron
Butane torch or high power soldering iron
Electrical solder
Wire cutters
Multimeter (optional)


My writeup:
*For the more delicate soldering, I used a Hakko FX-888D soldering station, but any decent soldering iron or lower power butane iron should work.
*For the heavier de-soldering work, I used a butane soldering iron with a torch tip on it. The old and heavy solder used to seal the tip of the canister and also to hold the canister in its retainer ring took some serious heat to melt. The torch also made it easier to re-solder the canister into the retainer ring.

1. Remove fuel pump assembly.

2. Remove fuel sender assembly from pump. At this point, I dropped the fuel pump assembly back into the tank to keep anything from getting into the tank and keep most of the fumes from escaping.

3. Let everything air out for at least a few hours - you don't want to be working on something that still has fuel vapor all over it.

4. If you have a multimeter, now is a good time to just sanity check things. Check the resistance between the red wire (float) and any metal piece on the sensor housing. From what I remember, this should range from ~5-10ohms with the float all the way up to about 110-130 ohms with the float all the way down. That is what runs the fuel level gauge.

To check and verify that the low fuel sensor has failed, check the resistance between the clear/copper colored wire and the "nib" (the very end) of the sensor. At room temperature, resistance should be between 900 and 1000 ohms. As it heats up, that resistance would go down.

5. After you verify that the low fuel sender is actually bad, you'll want to de-solder the cylinder from its retaining arm and then unwind the write, open up the clip holding the wire to the assembly, and then the low fuel sensor and its wire should be completely free from the rest of the assembly.

6. Using some small pliers and maybe a small screwdriver and hammer, gently start working your way around the canister's lip, bending it out enough to allow it to release the "disk" that the wire goes into. Once that is released, you should be able to get a look at the thermistor which runs the show. It's VERY likely going to be in two charred pieces, otherwise you wouldn't be reading this or doing all this work.

7. De-solder the top half of the old thermistor or cut it off close to the "disk". You don't want to leave anything except some bare clean wire or a clean piece of metal you can solder onto later.

8. De-solder the tip of the canister, remove the other half of the old thermistor from the canister, and ensure the middle hole of the canister is clear of solder.

9. Bend out the wires of the new thermistor (if needed) so it is in a straight line. Lay out the thermistor so that the "bead" of the thermistor will sit roughly in the middle of the canister when you're done. Trim the side that will be soldered to the "disk". Leave the other side long.

10. Solder the short side to the "disk". To ensure you have a good connection, check the resistance between the ring terminal of the wire and the long side of the thermistor. It should be 900-1000. If not, your soldering job might be bad. To get a consistent reading on my project. I had to firmly hold the test leads onto the wire, otherwise the reading wouldn't be consistent.

11. You should now have a wire with the "disk" from the original sensor on it and the new thermistor soldered to it. Slip this into the canister, passing the long wire remaining on the thermistor through the center hole in the canister. Solder the wire into the center hole, making sure to get a good connection for the wire on the canister, but making sure *not* to plug any hole except the center one! We have to have fuel flowing through the canister to allow the sensor to work!

12. After soldering the thermistor to the end of the canister, you can again check the resistance between the wire ring terminal and the end of the canister. It should be 900-1000 ohms.

13. Using the same combination of pliers, flat head screwdrivers and sheer determination, fold the top of the canister over the disk as well as possible, trying to keep from damaging the disk or canister in the process. I managed to get mine to hold the disk pretty snugly...

14. Re-insert the canister into its retainer ring and solder it onto the ring similar to how it originally was. Wind the wire around the shaft like it originally was and clip it back into the retainer. At this point, everything should look about identical to when you started.

15. Re-install the sensor assembly onto the fuel pump assembly and hook up the two sensor wires (red for the float should go in the middle, the clear/brown wire for the low fuel sensor should go to the back terminal [the one closest to the sensor assembly that you just bolted on]). DO NOT HOOK UP POWER TO THE FUEL PUMP!! REMOVE THE BLUE WIRE POWERING THE FUEL PUMP IF YOU WANT TO DO THIS TEST!!! If not, just install all wires and put the pump assembly back into the tank.

16. To test the low fuel light, leave the fuel pump assembly out of the tank and turn the key on. As long as the fuel pump power is not hooked up, this won't do any damage, but it will simulate the conditions that the low fuel sensor sees when the tank is low. It took my low fuel light somewhere between 30 seconds and a minute to start lighting up. I actually thought the sensor didn't work when I first turned the key on....but it just took longer than I expected for the thermistor to heat up enough. Anyway, if you don't have the low fuel light on within about 2 minutes, then something is definitely wrong. If you're sure the thermistor repair is right, I'd suggest checking the bulb and solder joints in the warning light/clock assembly.

17. If your test worked, turn off the key, reinstall the wire for fuel pump power, and put the pump assembly back into the tank.