Fuel sender resistance settings?

I believe the factory sender used 73-23-10 ohms for empty-1/2-full. Has anyone made these same resistance measurements on reproduction senders?

It took me having 4 units shipped from 2 different vendors to get one that was in spec. I learned to test them after the 2nd dud.

Vans Auto provided the one that actually worked, and it was the 2nd one they shipped. I bet if you called them, they would do the same on the 1st one.

The ones from Classic were both had the correct readings in way less arm travel. The 1st Vans one went to infinite resistance halfway through travel.

Vans tested the 2nd one they sent me before shipping. I now have my original 5/16" sender and three 3/8" senders that don't work. No one wanted them back, Classic just gave me a store credit, including the shipping cost which was cool.

I just checked a new one (not sure what brand) & got 13/88

Hearing this concerns me as I replaced the unit in my Challenger because the original had failed. Since I'm redoing a bunch of other stuff, I haven't put power nor fuel to it to test. If my replacement isn't right, that's kinda sucks. Do we have anything in the tech archives about testing and correcting these new units with the incorrect range?

I don't know about correcting, but easy enough to test. My sloppy editing made my response not so clear, but Van's tested the 2nd one they sent me before putting it in the mail. I double checked it and it prior to installation worked as it should on install. I'd guess if one were to call in the order and request that they test, they probably would.

Anyway, on the bench with a multi-meter on the 100 ohm setting, alligator clip one lead to the terminal and one lead to the "bulkhead". With the arm all the way up (furthest from the pickup) you should have ~10ohms (+/- 1ohm, per fsm). Move the arm down watching for a roughly linear increase and when the arm is all the way down, you should see ~73ohms (+/- 12ohms, per fsm). In the car, you could probably pull the filler tube and move the float arm up with something and do the check. I didn't try that, but I did go in through the filler hole (Barracuda) with a grabber to get the sock from the original pickup out of the tank. I did move the float in trying to nab the sock.

The float arm may need some tweaking to indicate correctly, though the one I finally got that worked that I got was spot on. I did, however tweak it to show empty with 3 gallons in the tank instead of two just to be sure the the pickup would stay covered while cornering with low fuel. This had the net effect of having the 1st 5/8 tank drop rather more quickly than the rest of the tank.

I did try tweaking the arms on the 1st two units I got, but best I could get was either never full, or never empty as it only worked on maybe half of the arm travel.

The 3/8" pickups are dicey to R&R in the car (though the Vans one was far easier than the other two, they are built slightly differently), I imagine a 1/2" pickup would have to be done with the tank at least lowered. The combined diameter of the pickup tube and float are a bit larger than the opening so some maneuvering has to be done to get it in. 5/16" pickup was a cinch to remove in the car.

Were you able to check 1/2 tank? My repro is about 14 ohms at full.

I just now got 43 EDIT mainly I want it to pretty much be dead on at the lower end so when it hits E that I have just enough left & a cushion (but not 10 gallons) to hit a gas station.

Over the winter I put a Spectra EFI in my 69' Coronet and fighting the same issue with their unit. I didn't check the readings when initially installed the tank and upon filling it with 5 gal of gas the needle didn't move past E on the gauge. Should have been near 1/4 on the gauge. I drained the gas and pulled the tank to check and adjust the sender as needed. Word of caution on the pickup/sender unit on the Spectra EFI tank.....go slow and keep your cool. Getting the unit out will try your patience and you may need to keep easily offended people away from you as your vocabulary will match the difficulty. At least it was for me. My kids heard some very interesting word combos during this process.

Once I had the sending unit on the bench I tested it and had to move the float arm and bend the limit tabs to get to the factory specs. Putting the unit back in the tank was probably 2x as difficult as getting it out....again...go slow. With the tank dry I flipped it over to have the float at max full and hooked up some jumpers to the frame and lead wire and hit the key. It read Full on the dash gauge and it would read 1/2 when I moved the arm (with a yard stick from the filler neck) to a line on the unit I marked based on Ohms for "Half Full". All worked fine throughout the range of the unit.

Reinstalled the tank and put a measured 19 gal into the dry tank. Hit the key and 3/4 full on the gauge and then hand to forehead. Even added an extra gallon to make total capacity 20gal and gauge stayed steady at 3/4. So, for now 3/4 is my Full mark until I dare to try and tackle it again.

The tank is grounded well through the tank straps and even has a ground wire from the unit to the frame, so that is covered and not the issue. It may be in the dash or needs to be cycled a few times through the ups & downs of the fuel level in the tank. I only have about 30 miles of driving on the new tank and time will tell with more miles and fill ups.

^^^ this tells me that the next one I do I am gonna with the tank still outside fill it with water & go thru the checks to get/confirm that the sender reads right BEFORE the install. thank you for the heads up.

I've also thought the high resistance position was 90 ohms but all my stuff is from the 70s and I can't tell you if earlier years were a different resistance. I will mention that it is often possible to peel the cover off the rheostat portion of the sender to clean up the mechanical contacts and tweak how the blade sweeps across the coil. Not exactly the same net effect as bending the float arm but same idea. Resistance changes should be linear as the wiper moves across the coil but if ya play with one on the bench, you'll see that's not always the case. The idea with tweaking the wiper is to get the sender reading 0-90 first, hopefully w/ 45 at the center and then tweak the float arm to line up.

You might also find it worth the time to connect the sender to the tank wiring before installing it in the tank. Continue doing the bench testing and tweaking using the cars gas gauge instead of the multi meter. After you get the sender working [close to] right on the bench, if the gauge isn't reading the way you expect, chase the body wiring issues until it does. The most common problem I have with that is the chassis ground connection at the tank. With Dodge trucks the bulk head disconnect is often a problem too.

Get all the electrical working then put it in the tank and work on getting the float arm to land where it should.

Very nice, I have never seen that spec chart..

Thank U.

Just my $0.02...

I also put a Spectra efi tank on my 74 Challenger. Before I installed the tank, I made a half hearted attempt to remove the sending unit / pump assembly. I didn't readily see a way to get it out unless I drilled out a couple of rivets so I just sealed it back up and put it in the car.

It seems to have roughly ten gallons in it when the gauge reads one quarter.

I don't know how different the Coronet tank is from the Challenger tank, but I would like to hear how you removed yours.

I think it may be easier to reassemble a 1911 or AR platform blindfolded when compared to getting the pickup unit out of the tank....and back in without mangling it all up. It was about an hour of trial and error in getting the correct angle and "push/pull" on pump base. The biggest hang up is the rubber nipples that protrude from the isolation seat/bracket. Those little things will hold it all up from coming out. The locating tang cutouts are your friend on the tank and that is where you have to line up the arm and other larger pieces. It comes out at a position of 90* or more when you figure out the combo. The plastic float WILL come off and so be ready to fish it out and PRAY that the small lock washer that keep the fuel sock on does not come off during the removal.

The sender for the spectra tanks is way off. Did a EFI tank from them and took the sender out and messed with it. Best I could get it down to was around 30 ohms, reads around 3/4 tank when full.

I have a spectra as well out of the car I am going to test. In order to get the sending unit and pump out you have to twist it around.

I converted my Challenger from 5/16 to 3/8. Getting the sender out and back in is not too difficult, even with the tank installed. I put the car in the air, remove the right rear wheel and sending unit is accessible right there. Knock the retaining ring loose and work it out the hole. Now, that doesn't mean I'm looking forward to messing with it, but at least I don't have to drop the tank. But this is the stock tank and stock style sending unit for a carbed application.