Fuel gauge and sender

[raleighstang65]

I've posted about my fuel gauge troubles a few times now... Time to revisit it! Brief history- Gauge never worked since I bought the car two years ago, replaced sender.... still no reading, replaced IVR... still no reading, replaced gauge... still no freakin reading! So tonight I grounded the wire at the sender and turned the key to 'on' for a second and the needle moved!
From my searches on here I've read about making sure the tank is grounded well. I'm just not really clear on this part of it. It's the original tank and the trunk hasn't been resprayed or anything. How do I check to see if the tank is properly grounded?
Does it seem like I'm finally on the right track to nailing this problem down? I'm in the process of installing new Autometer gauges and would really like for that pretty new fuel gauge to do more than look cool!

 

[BarnStang]

The tank has more than several bolts holdiing it in place. Unless it's rusted to near falling apart, it should be well grounded. If you feel it's still a concern, loosen them up and retighten them. Make sure you have a good connection from the neg batt term to the block, and a good clean ground strap from the block to the firewall, and there should be a ground connection behind the inst cluster that has a ground wire with a little sheet metal screw in it to the dash frame. I had a customer with a HUGE gauge problem in a 64 Galaxie. After multiple gauge replacements, IVR replacements, it was the neg batt cable bolted to the alt bracket...believe it or not.
You say you grounded the wire at the sender and the gauge moved. Did it swing full scale? It should move somewhat slowly-damped by the IVR. If it swings full scale, the problem just about has to be with the new sender in the tank. The sender "can" be installed upside down if you try hard enough.
If you are switching to an aftermarket fuel gauge, other than good grounds, you will need to follow their directions for the gauge to work in that application.

 

[raleighstang65]

Barnstang- Thanks for the quick reply. I only turned the key on until it started to move. I'd read to not leave it on too long but it was definately moving towards full slowly. The sender is in the right way, only problem I had when I installed it was draining the gas out... had a few more gallons then I had figured was in there, lesson learned on that one though... use a bigger freakin bucket next time just in case that last 5 gallons you aren't counting on spills all over the garage floor!
Can a sender crap out if it's only a year old (guess it never worked though)? No other electrical problems aside from the fuel gauge. My temp gauge didn't work for a bit but turns out I didn't have it centered in the bezel when I had the cluster pulled trying to fix the fuel gauge. Temp gauge works fine now.
I didn't install a new retaining ring for the sender, could this be part of the problem if it's a grounding issue?

 

[BarnStang]

As long as the rubber seal is under the sender,and not under the retaining ring, it should have a good ground. You can always clip a ground lead to the metal ring, but I would be surprised if that were it. Worth a try. I've grounded the sender lead before on lots of cars. It goes all the way up there when the tank is full...granted you lose the resistance of the sender. But I wouldn't leave it hooked up like that, but seeing if the gauge swings full scale and yanking the clip off should not cause any problems. I would still lean towards the sender. Most any shop will tell you that parts are half the battle in fixing cars. At least check the plug at the end of the wire. Is it good and tight on the sender post? Not half falling apart and corroded? Good moderatly clean metal inside the plug end? Sender wire not getting pinched inside the car anywhere? Not sure the routing in a coupe. My vote is for a new sender. New does not always equal good...

 

[69gmachine]

Since you can get the needle to move by grounding the lead, it is definitely the sender. There are a 3 things to check for:

1) The float could have a hole in it and be sinking to the bottom. I had this problem with a brand new brass float. Just because it's new doesn't mean it's good.

2) The arm could be bent such that the float is not able to raise up where it should be. If this is the problem you should see the needle at least move up to empty when you have a near full tank.

3) check the resistance of the sending unit (when it's out of the tank) and verify you have 10 ohms when the arm is all the way in the full position, and 77 ohms when all the way in the empty position as measured from the stud where the wire lead attaches to the flat plate that would go to ground.

I just rebuilt an original '69 low fuel light sending unit. It took several tries to get the arm and float in the right position to give an accurate reading. Be patient, you can do it.

 

[raleighstang65]

Alright, making progress here... I hope! I finished up the new gauges today and went out to the garage this evening to see what they looked like lit up. I noticed that the fuel gauge just BARELY comes to life when I turn the key. They are Autometer gauges and it doesn't have to move much to get to Empty.
So does this look more like a float adjustment problem? If the float needs an adjustment what's the best way to go about this? Drain the gas, adjust the float, put gas in, check gauge, drain gas, adjust float, see if I got it this time?
Appreciate all the help! I feel like I'm so close just not there yet...

 

[69gmachine]

Alright, making progress here... I hope! I finished up the new gauges today and went out to the garage this evening to see what they looked like lit up. I noticed that the fuel gauge just BARELY comes to life when I turn the key. They are Autometer gauges and it doesn't have to move much to get to Empty.
So does this look more like a float adjustment problem? If the float needs an adjustment what's the best way to go about this? Drain the gas, adjust the float, put gas in, check gauge, drain gas, adjust float, see if I got it this time?
Appreciate all the help! I feel like I'm so close just not there yet...

Make sure your aftermarket fuel gauge is designed to work with an early Ford sending unit. A lot of the catalogs only list a GM gauge which reads in reverse to a Ford and on a different voltage scale. With the sending unit lead grounded, you should be indicating full scale past full. If that isn't working, you need a different gauge.

When you have the sending unit out, make sure it reads the correct resistance at the ends of travel. If the sending unit is good electrically, and the gauge is matched to the sending unit, then the only thing left is to make sure the float is not sinking, and the arm is bent correctly. Yes it is trial and error. With my 69 I have a 20 gallon tank with a drain plug. I use a 5 gallon gas can and adjust it to read a 1/4 tank. I drain it back into the can until it's set right. Sometimes I spill gas all over my garage floor and curse like a sailor because the o-ring didn't seat. Yes it's a pain. If anyone has a "trick" to do this job easier, I'd love to hear it as well.

 

[raleighstang65]

Appreciate the help guys. I'm pretty sure the gauge is the correct one, I made sure I ordered the correct resistance for a Ford sending unit. My tank does have a drain plug but I can't get it out, PO must have tried to take it off at some point and rounded it so I can't get a grip on it. So I know what you mean about cursing it like a sailor! Basically I try to syphon out as much as I can then just pull the sender and let the rest gush out... I aimed for the bucket but ended up covered in gas anyways. Thanks again for all the info guys, definately have better knowledge to trouble shoot some things now!