1G AWD fuel sender solution!

[Drewpy Dawg]

I recently cleaned out my fuel tank after it sat for 20 years with a few gallons of old gas in it. It looked like a serious mess at first and I thought I was going to need a new fuel sending unit at the very least. Fortunately for me I was able to save my sender and get it working properly. (I can make another post about what I did to save mine that may be helpful to others if anyone is interested.) Even really nasty looking ones may not need to be replaced. However, if you really do need a replacement there is the issue of finding a good used one and what it will cost.

I figured there must be another car that uses a sender that might work for us with some modifications. Denso made our OE senders, and senders for many other Japanese cars. After some searching I found that mid-80s Toyota Corollas have a sender that looks nearly identical to ours. The top plate is completely different, but the most important part for our purposes is the variable resistor. The Corolla sending units are available cheap on eBay (albeit aftermarket Chinese made copies, not original Densos) so I spent $20 on one to experiment with. Here's what I found.

The housing of the variable resistor is basically identical to ours. It is held to the top plate with two small spot welds, so it should be a simple matter of drilling those out and separating it. The rod holding the float is shaped slightly differently and the float sits on the opposite side of the rod from ours, but that could be massaged if necessary. It also uses the same kind of low fuel sensor that operates the dash warning light.

But will it work with our electrical system and gauge?

Fuel sender specs in the FSM
Full - 3 ohms +/- 2
Empty - 110 ohm +/- 7

My original fuel sender reads 3.4 when full and 116.3 when empty, so working properly within spec.

The Corolla replacement sender reads 5.0 when full and 110.6 when empty. Within our spec!

So we have a fuel sender that is cheap, readily available new, and works in the same electric range as our originals. No, it is not a direct replacement, nor is it a Denso unit. Some minor modifications will be necessary, but most of us have done far more complicated things on our cars many many times. Figured I would put this out there for anyone who runs into the need for a replacement sender and either can't find a good one or doesn't want to spend over $100 for a used one that's probably still rusty. Below are the pics comparing my original sender to the Corolla one and my tests with the multimeter.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

 

[Car Cannibal]

Great detective work.

Is the low sensor the same length as the stock one, like it'll read fuel in the same spot in the tank?

My float arm is jacked so my fuel gauge isn't accurate so I go off of mileage and low light but I'd like to change all that if possible with a new arm etc. Thanks

 

[Drewpy Dawg]

The low fuel sensors look to be at slightly different lengths. I'm going to swap the sensor from the new sender onto my old one because my old sensor doesn't work. I'm not entirely sure how I'm going to achieve that but will be working on it today and I'll post if I come up with a good solution.

 

[Car Cannibal]

I'm trying this out soon, I'll report back with one I found as a genuine Toyota Corolla on Ebay so I can get many years out of it vs a possible junk knock off and I paid everyone to get out to talk to Haltech and pull the tank.

 

[Car Cannibal]

Any update on this, gauge rewards correctly, low level accurate?

 

[Drewpy Dawg]

I did not install the Toyota unit. As I said in my original post I was able to save my OEM sender which is now working fine. I don't see any reason why the Toyota unit won't work with our gauge as it reads within the specs for our OE sender. It's definitely not a drop in replacement and will take some creative modifications. The body of the sender will bolt up to our fuel hanger. It looks like it may be possible to swap the float arm. The biggest issue is the electrical connection. The Toyota unit has a plastic connector on top with a terminal riveted to it. If you carefully drill out the rivet you can remove the terminal. The terminal is attached to a very thin wire from the sender's winding. If you're good with such things I think you could strip the end from a length of 20 gauge wire, tin it with solder, and then attach the thin wire from the sender. Put some heat shrink over it, crimp a ring terminal on the other end of the 20 gauge wire, and bolt it to the OE hanger just like ours were from the factory. I did not go that far down the path since I didn't need to use this one, but I wanted to put the info out for others to try. Let us know what you come up with.

 

[Car Cannibal]

Thanks, was hoping someone would've done this and had a heads up on the mods and results. I'll probably do this in Feb and post back, seems like it's possible but needs some know how to pull off the wiring. Then a tweak to the low level to match the factory location and this might work.

 

[Car Cannibal]

This was only great in theory, not easy, not fast, definitely not cheap and it's not registering the low 2gal level correctly so total fail for the time/ money invested. I should've learned by now.

I could've had a company make us a custom float for all this in the end or just leave the stock broken and moved on, people on here have spent more for a full running car.

 

[erikoberdorfer]

Hello
I am running into an issue with my 1g awd low fuel light sensor on my oem sender assembly. The fuel level sensor portion works fine. I can test this with the sender unit removed from the tank and plugged into the wiring harness. Here I can see changes to the float arm position translating to fuel gauge changes (moves the needle from E to F). However, with the sending unit in free air with the level arm all the way down and the gauge reading empty, the low fuel light on the dash never comes on. I jumpered the black wire pin to the yellow with stripe pin in the harness, and this illuminated the low fuel light in the dash. Therefore I know the light works, but the sensor that detects the low level doesn't seem to.
Do you think this mid 80s corolla sender's low fuel light sensor would adapt to the 1g awd sender and work? I have yet to find a replacement (1g awd sending unit) to fix this.

 

[Drewpy Dawg]

Here's the proper way to test the low fuel sensor. It's not a simple switch, it's a thermistor, so you can't just check it for continuity like other switches. Using a 9 volt battery and some test clips connect it as follows:

Battery negative to ground of sending unit.
Battery positive to a 12 volt light bulb, such as a circuit test light or a light bulb from an aftermarket gauge.
Connect the other side of the light bulb to the wire from the low fuel thermistor.

It will take anywhere from 30 seconds to a few minutes for the light bulb to begin to glow. As the sensor heats up it begins to conduct electricity and the bulb will slowly brighten like a dimmer switch. With all the wires still connected, submerge the low fuel thermistor in a cup of water. The water cools the thermistor and the light bulb will go out.

 

[erikoberdorfer]

Hello,
I tested the thermistor on my fuel sending unit via the procedure listed above. I used an old gauge. Unfortunately the thermistor never allowed the gauge to light up. It seems like the thermistor is the issue.

 

[Drewpy Dawg]

If you Google “fuel level thermistor” there are a bunch of options for buying a replacement.

 

[92AWDHX40]

Im in Detroit ill look for one Monday

 

[erikoberdorfer]

All,
I was able to repair the oem low fuel level sensor on my existing sending unit. I am using a JMF bolt in fuel cell with a sump feeding an external pump. The JMF unit allows the factory sending unit to bolt in place and plug in, so the stock fuel gauge works (fuel level and low fuel light).

As described above I found the level side of the sender to work fine. The low fuel light side tested out to be defective per the test procedure outlined by Drewpy Dawg. I then decided to actually disassemble the low fuel light sensor / thermistor. I followed the guidelines I found on this page https://xs11.club/forum/miscellaneous/miscellaneous-tips/875854-fuel-light-thermistor-repair

When I removed the crimp on the top of the little metal container as described in the link, I discovered that my thermistor was broken in half. I was able to purchase a package of NTC thermistors from amazon. There were multiple ohm ratings in the pack, and I chose the 1K Ohm one. Using the information in the link I provided I replaced the broken oem thermistor with the new one (after bench testing the new one). This fixed it and everything works now.

 

[92AWDHX40]

Oh yeah I'll see you in Ohio in September with my baby.

 

[erikoberdorfer]

Victor,
I am looking forward to it!