Got stranded on the side of the road today by the Superbird - Dam fuel gauge!

[70Sbird]

I went home at lunch today and at Noon, the sun was shining so I drove the 'Bird back to work!  Great day but a little hot. About 3:00 the skies turn gray and it looks like rain is moments away. I pack up my stuff and head home early. By the time I get to the car it has started raining, but not too heavy yet. I make it about two miles and run out of gas. By now it's pouring.  I call my wife to find the gas can, and bring me some fuel (she was thrilled). While I sit on the side of the road, in the rain, with the windows fogging so much I can't even see he when she pulled up, enjoying the moment.
So what is the deal with fuel sending units? Since I bought this car in 2001 I have never managed to get an accurate fuel tank reading. Here is what I have done so far:
I replaced the tank, sending unit and hardware as a package when I replaced the trunk floor in 2006. Old gauge (also likely a replacement) read between 1/2 and 3/4 when full and at empty I could only squeeze about 12 - 13 gallons in the tank. New gauge and tank read about the same. I sent my gauges off for cleaning/facing/repair last spring and ended up with another fuel gauge. I also used a new ground strap, checked all connections and resistance between gauge and sender, all check out. I also spent some time bending the float arm, trying to "tune" the sending unit.
If I ground the sending unit lead at the sender, the gauge swings all the way to Full.
Last fall I filled the car up the night before I left for Talladega and was greeted with fuel dripping out of the sending unit wire connection. Fortunately I never throw anything away and popped a new float and gasket on my old sender and put it back in, all the way to Alabama and back with no leaks, but the same incorrect readings.
So where do I go from here? I've replaced every component at least once and still can't get this right! I have now had to have my wife come and rescue me twice in the last 18 months with a can of gas, She is not impressed and I'm beyond frustrated.
Am I the only one with this issue? I seem to remember a thread or two about repop sending units all being crap, but someone has to have this figured out!

On a positive note, the windshield I had installed just before Talladega last year that leaked, and was re-sealed is now watertight!

[oldcarnut]

Here's some stuff I went through on similar problem in the gauges section.  Maybe it may offer some help. http://www.dodgecharger.com/forum/index.php/topic,57376.0.html

[70Sbird]

Oldcarnut,
Thanks for the links, Those are the threads I remember reading I just didn't think they were from over a year ago! So, the two fixes so far are your reworking of the float rod and 1 Hot Daytona's solution of welding an old/NOS float/sender assy onto a 3/8 pickup tube. Both of these threads are over a year old, has anyone seen an updates from the aftermarket? I can't believe (well I guess I can) that no one is reproducing 68 -70 B Body sending units that work!

[69Charger500]

Every 69 or 70 Charger I've owned has the same problem; stopped trying to fix 'em 25 years ago.

Full tank reads 3/4, quickly moves down to 1/4 after 50-100 miles.

Empty "E" is good for another 50-100 miles; gauge goes waaaay below empty...

When I can't take it anymore, I fill up, 12-13 gallons max is all I've ever gotten in it before it starts filling up the fill tube.

Back to 3/4 again, and start all over; never ran out with the '69 (yet), but I'm tempted to run it low, throw a can of gas in the trunk, and see how far that gauge goes below empty before it finally runs out...

[oldcarnut]

Oldcarnut,
Thanks for the links, Those are the threads I remember reading I just didn't think they were from over a year ago!

Your welcome. On the other hand it only reminds me of how much time has passed by and I'm nowhere near completion of a build I thought would have been done this summer   .  Maybe next summer.

[hemi68charger]

Man Scott, that stinks............. Hopefully it all panned out by the end of the day..........

[pettybird]

The Petty car's gauge used to go below empty, but I took the gauges apart, refaced them, cleaned them, and now it runs out ABOVE empty!  Ask us how we know   

[70Sbird]

The Petty car's gauge used to go below empty, but I took the gauges apart, refaced them, cleaned them, and now it runs out ABOVE empty!  Ask us how we know   

Doug,
Same deal here! the needle was just a hair above "E" on my refurbished/refaced fuel gauge as I coasted to a stop. I just "knew" it still has gas in it!
I guess I just need to keep it above 1/4 tank.

Scott

[hemi68charger]

I'm going to take my 5V bench power supply and for sure create a circuit with the sending unit and gauge in it and TEST !!!!

[70Sbird]

I'm going to take my 5V bench power supply and for sure create a circuit with the sending unit and gauge in it and TEST !!!!

I read somewhere that if you get 2 resistors: a 75 ohm, and a 10 ohm (limits on a factory sending unit?), you should be able to connect them between the sender lead (unhooked) and a good ground. With the key on, the 10 ohm resistor should make the gauge read full, and the 75 ohm resistor should make the gauge read empty. If these two tests work, the gauge, power supply and sender wiring should be OK, leaving the sending unit and sending unit ground as suspect

[70Sbird]

Just an FYI,
I came home from work and checked the FSM, mother Mopar specifications for the fuel sender are:

Full: 9.6 ohms +/- 1 ohm
Empty: 73 ohms +/- 12 ohms

So, using the 10 and 75 ohm resistors as I described above should be spot on and should isolate the problem.
Scott

[Dans 68]

I picked up a resistor substitution kit (http://video.ap.org/?f=VAAJN&PID=au_QX5_MKl9_fNSdhZR7GPATadkbyaHu) to get pretty much every resistance I would need to fine tune my gauge. It is a work in progress... http://www.dodgecharger.com/forum/index.php/topic,72497.msg813537.html#msg813537

Dan

[Kismgby]

My gauge used to be a smidge off - y'know, at FULL it would be just a needle below the mark, and EMPTY would be a tad below the other mark.  I was happy with this.  Would always get fuel when it was reaching the E marker and never had a prob.  Then someone decides to do me a favor and "fix" it.     Lasted all of, um, two days.  Now I'm always on E and just keep a record book of mileage at fuel stops.  Every 100 miles, I'm in search of fuel. 

[hotrod98]

That must have be difficult to keep up with on Power Tour.

[hemi68charger]

Here's the set up I have.. I'll replace the resistor box with the sending unit and see what happens............ I can make sure first of all that the gauge is accurate by making sure: As Scott has pointed out......

Full: 9.6 ohms +/- 1 ohm
Empty: 73 ohms +/- 12 ohms

If this holds true, then it's time to replace the resistor box with the sending unit... Not sure if being submerged in fuel affects the resistance values... That's one part of the simulation I won't attempt..........

[70Sbird]

Troy,
what resistance value are you using to get the 1/2 tank read on your gauge?
Scot

[69_500]

Glad I haven't had that problem yet. Luckily my gauge reads pretty accurate because last time I drove the car and it was down close to E it took 18.7 gallons to fill it up. I'm thinking thats pretty accurate on the gauges part.

[hemi68charger]

Troy,
what resistance value are you using to get the 1/2 tank read on your gauge?
Scot

Scott,
Sorry I didn't get the value to you today... Got wrapped up with life.... I'll get the book I have out tomorrow (Wed.)..

[hemi68charger]

Hey Scott,,,,,
What I have is:
E       73.0
1/2    22.8
F       9.6

[70Sbird]

Hey Scott,,,,,
What I have is:
E       73.0
1/2    22.8
F       9.6

Thanks AB, I'll have to run by the local Radio Shack for the "middle" one, but I just want to verify one more time that my sender is the culprit!
Scott