NEW Gas Tank Sending Unit not working

[oldchevelle541]

Greetings, purchased Dodge Coronet last fall and when the video of the car was sent to me ahead of shipping gas gauge inside showed to be working. Once car arrived gauge did not work. I just attributed it to the 400 mile ride and getting josseled around in the transport trailor. Purchased new stainless sending unit from Classic Industries Part MF272 and installed. Gauge does not work.

Before installation I took the wire to the gauge and ground to Chassis and it worked hence not the gauge.

What should I be looking for.

[birdsandbees]

Tank/sender not grounded.

[Canadian1968]

As long as your temperature gauge is working as well you can ignore the voltage regulator as the culprit as well. Check that the sending unit is grounded as already mentioned .

You can also test the resistance of the sending wire. There is a plug connection bwhine the drivers side kick panle. It runs the wires for the lights in the back of the car as well as the wire that goes to your sending unit from your gauge cluster .

Check to see what the resistance of this wire is 80 to 75 ohms will be empty 10 is going to be full .

Your gauge will never read correctly with the new after market sending unit. Unless you have the gauge itself recalibrated .  With the new unit it uses a linear resistor connected to the float.  While the empty and full resistances are correct everything in between is way off. 

The factory gauge is calibrated to read 25 ohms for 1/2 tank . With the new sending unit half way threw it's travel will give you roughly 40 to 35 ohms depending on the unit. The will show an approximate 1/4 reading on your gauge when you actually have 1/2 in the tank.  Bending the float rod will only move the error reading . You may get it to read 1/2 properly but now your full and empty will be wrong .

The gauge itself must be calibrated correctly

[oldchevelle541]

Thanks all, all other gauges work properly hence will recheck grounds and wire behind kick panel. We took the new sending unit back out of the tank and bench tested it to make sure it was working and it was. The old sending unit was dead and regardless of where the float position was no change in ohms reading. I am sure it is something simple but will keep trying. I do not mind if gauge is not accurate but anything better than showing an E reading.

[oldchevelle541]

Spent a few hours under the car today trying different things.

1) I disconnected lead wire from sending unit and grounded it to chassis. When I turned the key it went from E to Full fairly quickly leading me to believe both wire and gauge are in good working order.

2) Put an ohm meter on new sending unit with lead disconnected and it was reading about 50 ohms suggesting I have a little over 1/2 tank.

3) I then took an old wire and wrapped the outlet tube on sender and connected the other end to rear shock bracket. When I turned the key needle moved about 3/16" then stopped.

Any other suggestions. With the sending unit being stainless from Classic Industries does the make of the ground wire have to be different.

[green69rt]

Does your car have the grounding strap like a charger?  There is a grounding strap that goes from the nipple on the level gauge to the metal of the fuel line.  Do you have it, here's one source?

https://521restorations.com/Sending-Unit-Ground-Strap-for-all-1964-1978-Mopar-cars-short-375in-style/

[Canadian1968]

50 ohms would be under half tank. Remember higher resistance is LESS fuel , lower resistance is more . That's when you ground the wire your basically giving the gauge no resistance so it shoots up to full.

So your gauge is probably reading about a needle width off empty maybe little less?  That unfortunately is correct for the miss match between the gauge and the sender .

[oldchevelle541]

Thanks green69rt.

How does that part stay tight to the fuel lines. Does not look flexible or spring loaded or appear to be semi circular for a snug fit. I am curious why all these grounds on line are 3 3/4". Since my sending unit is stainless do I need to get a stainless ground.

ps: I tried grounding the sending unit from the outlet tube to the chassis and it did not work using a simple wire. Is there something unique with this part in grounding to the fuel line forward of the rubber hose ?

[Canadian1968]

You do need a ground of some sort. Just leave the wire you already have / had on there.  Buying the the oem one isn't going to do anything different except cost you some extra money.

There is nothing special about the ground. I personally use an extra metal hose clamp with an 8 awg wire soldered to it, around the outlet tube on thesender . Then Up to the first mounting clamp of the fuel line that bolts to the rear shock reinforecment . The rest of the fuel line also ground with all the push in clips that hold it up to the front of the car.

[Nacho-RT74]

on my 74 the fuel sender allways worked, with factory sender and the replacement piece once my original said bye, with and without ground strap. I ended getting one strap just for correctnes and installing, but before get it I added a single wire inserted into the hose against the gas lines ( at sender outlet and body line ) and also worked. The gas tank straps it uses to be fairly enough, the ground strap is only a reinforcement




which is true, is the reproduction/replacement pieces are not a piece of art on how they are manufactured. Once I missed the reading on gauge, give a kick to the tank, and got back the reading LOL... points inside the rheostat assembly could be missing contact at certain points.

[Nacho-RT74]

and to test the fuel sender...
max reading is 10 ohms +/- 2
min reading is 72 ohms +/-5

( Chebbbbbbies are 0 to 90 or so as far I recall )

[b5blue]

Stainless has no spring grip, just ground the sender with tie wire twisted tight to test. 

[oldchevelle541]

Thanks all, good information. I did find an 8" lg OEM ground from Year One for under $10.00 with free shipping. The extra length over the st'd 3 3/4" gives me some flexibility and you can't go wrong with free shipping. I will add some additional ground using wire if needed. I will advise if I get it working this weekend.

[Lennard]

Thanks all, good information. I did find an 8" lg OEM ground from Year One for under $10.00 with free shipping. The extra length over the st'd 3 3/4" gives me some flexibility and you can't go wrong with free shipping. I will add some additional ground using wire if needed. I will advise if I get it working this weekend.

YearOne and free shipping?

[A383Wing]

the reproduction aftermarket sending units will never work correctly....there's another thread, actually many threads about this....in one of them I had posted where to send your OE sending unit to get repaired, correctly....I just can't remember the name of the company

Bryan  (getting old sucks)

[Nacho-RT74]

I don't think the problem is the absence of the ground strap. That is just a reinforcement, but the tank itself is able to get enough ground throught the mounting straps to make it work. I think there is something else on this.

[oldchevelle541]

Quick Question.....even though lead when grounded will make gauge needle move to full is this enough to know wire is absolutely good or should multi-meter show a power reading going through the wire. Just a thought. If yes what reading should I measure with meter and what setting should it be set to ?

Electrical is not my strong point

[Nacho-RT74]

ok, I'm not sure If I'm getting the question. If you ground the fuel sender wire ( the blue one coming throught the trunk floor, which conects to the fuel sender ) the gauge will pegg out to max. That will discard the wiring, plugs and everything related between gas tank and gauge itself. Actually will be over full, because the straight ground is allmost close to 0 Ohms, where the max reading from fuel sender is 10 +/-2 ohms.

to check the sender itself the correct way would be on bench, between anywhere at the chassis/housing and the terminal outside with multimeter in Ohms position. Moving the floating arm it should change on the range mentioned.

You can check it mounted on tank on the same way but will read just one mesurement: the reading stricted to the actual gas content. Of course if you get any Ohms reading between the range ( 10-72 ohms ) it means it should give the signal to the gauge.



Replacement pieces are not a piece of art and is not weird the readings are not exact. In fact, sometimes they doesn't work in all the range and need to be opened to make the points tab/shoe make the correct contact with rheostat on all the shoe travel over the rhesotat/variable resistor coil ( BTDT ). I had to make it on the repro piece I got from VANs. I played with it also giving it some twists here and there to the assembly to get a better range measurement, but that was just a personal challenge.


The reading on stock pieces are progressive/geometrical, while as far has being told, the replacements use to be more linear. In my case I'm not that picky with this as far the FULL and EMPTY readings are quite good. If I have 2/3 on gauge but I'm having 3/5 on tank, That wouldn't important to me. Gas is allways moving and floater with it, Gast tank isn't flat either so the gas level is allways just a reference measurement.

[Nacho-RT74]

Thanks all, good information. I did find an 8" lg OEM ground from Year One for under $10.00 with free shipping. The extra length over the st'd 3 3/4" gives me some flexibility and you can't go wrong with free shipping. I will add some additional ground using wire if needed. I will advise if I get it working this weekend.

YearOne and free shipping?

I never have seen those words on same phrase since 2002 which I'm on line with this!!!!

[oldchevelle541]

Gents,
again thank you for your comments and suggestions. I will work on it again this weekend and may come to realize the unit I purchased is flawed from classic industries, not just with accurate reading but simply not working at all. When you pay $99 for new in stainless because you want your ride to have premium parts it is my expectation that the part works as expected. We quickly bench tested it just to confirm ohm readings changed as you moved the arm but never thought to fine tune readings for accuracy. Again for the money I expect a drop in and go part.

I am with Nacho RT in that complete accuracy is not a big deal to me. I just want to know when I am getting close to putting in some 93 octane again.

[Nacho-RT74]

That's why I'm "satisfied" with the $50 ( or so )  unit I got from VANs... but that was maybe 12 years ago LOL. Senders for 71/74 were a recent release on those days everywhere and everybody had them in $120 rate being plastic floater and wired instead the metallic strap like originally is. VANs unit was more accurate ( brass floater and metallic strap ) and WAY cheaper. Some tweaks made the job better

[b5blue]

Keep in mind 1/2 a tank of fuel may not be 1/2 of the arm's sweep.

[Nacho-RT74]

thats parts of the non linear reading of stock system. Half tank should be on 25-30 ohms rate, which is not definitelly the half way arithmetically between 10 and 72 ohms. SOOOOO, he could try to set the half way of the arm trace and check the ohms there. Just for reference

[histoy]

I'm having a similar issue with a '56 Chevy BelAir that I just bought.  It has a standard gas tank sending unit (0-30 ohms).  The car has new Classic Instruments gauges (33 - 240 ohms).  Tanks, a company here in Iowa that sells reproduction gas tanks and sending units, also sells a MeterMatch.  It's an electronic device that allows you to match different gauges and senders.  You have 4 set points that allow you to match the dash gauge readings to the sending unit output.  I chose empty, 1/4, 1/2, and full for my settings.  It sells for $69.

In response to the question... does it need to be reset when the battery is disconnected or turned off?  No.  It doesn't have to be reset.

[b5blue]

https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=748/category_id=184/mode=prod/prd748.htm