Topic: 1966 fuel sending unit connection ? not working

[Hipo giddyup]

 So I'm really stumped on this one. I have read many posts online  about testing and checking fuel sending units and the fuel gauge and now it looks like I need to head down this path for myself. I never really had any issues with the fuel sending units other than to replace one that no longer works. In the this case its my latest project, a 66' 289 coupe, that has been sitting for a while. The gauge reading was fine before I removed the gas tank for some trunk repairs. However, when I replaced the tank the gauge no longer worked/read anything. I performed the check where you ground the sending unit wire to make sure the gauge responds, and it does. It pegs without issue. So I decided to replaced the dated fuel sending unit. The tank is fairly new but the sending unit, to my knowledge, was reused. I found that it was very corroded and the fuel filter/sock fell apart, so I decided to replace it with an aftermarket unit, a SD. After doing so, nothing. Not registering even with 5 gallons in the tank. So, I drained the tank, pulled the unit and tested it. On my Ohms meter it is reading a range from about 9 Ohms to about 80 Ohms with the range of the arm, and from my research online this should be correct. I then checked the movement of the sending unit outside of the tank. Using a long extension from the tank wire (so I can watch the fuel gauge) I tried moving the unit to make the gauge work. Nothing, then it dawned on me that something needs to be making contact with the vehicle itself. I let the gauge touch the side of the rear windshield molding (what I was close to at the time), and the gauge then gave a decent reading by me manipulating the arm up, then down, etc. This seemed to be working fine. So, I put the unit back in the tank, I cleaned the lock ring to bare metal so as to give a good contact point for the unit to ground to, and replaced about 4 gallons of gas. Uh..., nothing still... Now I'm at a loss. I did use strip caulk between the tank and the trunk lip and now I am wondering if it could be causing the poor connection? I can't imagine this as all of the screws and the one bolt that hold the tank in place are going to metal? Any help on this would be greatly appreciated.

[67350#1242]

A quick check would be to run a clip lead from sending unit body to a chassis ground point while mounted in the car.

[65Ford]

Perform a continuity check between the ground side of the installed sending unit to the chassis to check for continuity.  If not, break it down by checking between tank and chassis and another from the sending unit to tank.

[J_Speegle]

I did use strip caulk between the tank and the trunk lip and now I am wondering if it could be causing the poor connection? I can't imagine this as all of the screws and the one bolt that hold the tank in place are going to metal?

That should not be a problem. Might just be another defective reproduction

[Hipo giddyup]

Good point to do a continuity test. I was fooling with it some more but didn’t have my meter handy. I used a test light, attach the clip to a bare metal portion of the trunk lip (I had sanded to bare metal ) where the tank mounts and touched the sending unit feed/wire. The gauge went to full so I know the ground was good. I then touched the locking ring that holds the sender in place and even touched the metal body of the sender and the gauge stays at E , empty. I would have thought that this would have surely given me a reading? I’ll try the continuity test but it seems like there’s no other option than to pull it out and try to return it?

Can anyone confirm that the ohm readings of 9 -80 of moving the arm one way then the other is a correct range for this sender?

[midlife]

13 to 73 is the normal range, but yours is not that far off from that.

[Hipo giddyup]

Thanks midlife. So I’m at a loss of what to do other than return the unit.

[aaatp]

You should check continuity between the tank and the chassi if you haven't already. I suspect your tank may be isolated from ground.

John

[Hipo giddyup]

 Thanks for responding, I did check the ground from the trunk floor to the gas tank with my ohm meter and it read .4. I then checked the continuity between the fuel sending unit and the locking ring and it again read .4. I’m guessing that is acceptable? However, I have another fuel sending unit that I hooked up to the fuel sending wire , then I grounded the fuel sending unit to the body of the fuel sending unit already installed in the gas tank. At this point I was able to raise and lower the arm and my son watched the needle go from empty to full and even stop halfway where I had the arm in the middle of its range. I can only assume the fuel sending unit might be bad in the tank? Or, I’m now thinking the float could be filled with gas giving it an empty reading all the time? It will have to wait till this weekend until I can drain the fuel and start over with this newer fuel gauge that seemed to  give an accurate reading. Thanks again for all who reply, hopefully this info can help someone else out in the future. I’ll respond back to this post once I am able to replace the unit again.

[Hipo giddyup]

I continued working on this issue over the past week. I added an external ground from the body to the sending unit and even this did not produce a correct reading.  I ended up ordering a new gas tank since this tank is 25 years old and had a lot of chalky corrosion internally, I'm guessing from sitting. I also ordered a new tail light wiring harness since this existing harness had splices at the tail lamps and fuel sending unit. When I placed the fuel sending unit in the new tank I slipped a piece of wire on the arm of the sender just enough to be able to move the sender once the tank was installed and also loose enough that if you put more tension on the wire it would pull off. I ran the wire up through the nozzle inlet and after turning on the key, I could pull the wire, moving the sender arm, and verified that the gauge gave a reading. I filled the tank with 2-3 gallons but yet again, no reading. At this point my only choice was to take the fuel gauge out of the cluster and adjust the needle from the back of the gauge. Not the solution I was looking for, but after adjusting the needle, I finally have an accurate reading. I had appr. 2-3 gallons in the tank and the needle read 1/8 of a tank of gas. I then filled the tank to full and the gauge was over the full line on the "F". That I'm ok with. Not sure if the gauge lost calibration, or if the new sending unit is just not quite calibrated to the gauge? Either way the problem appears solved. Hope this can helps others down the road that might run into this issue.

[sgl66]

I put a new tank in a few years ago and had the same issue. 2 gallons of gas from a gas can and it showed empty. When i topped it off the needle was at F. I would rather be at E with 2 gallons in the tank instead of E and stuck on the side of the road.