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

[A383Wing]

found the company that rebuilds the OE bad sending units to as new condition and they work as they should

https://www.antiqueinstrument.com/

Bryan

[70 sublime]

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.

Does something like that need to be reset every time the battery is un hooked in the car or does it remember the settings ?

[oldchevelle541]

To all , thanks again for excellent feedback. Glad to know I have options. Here is photo of original unit disassembled to see what the problem was.

[b5blue]

See how the winding's are on a tapered backing board. That varies resistance. (Save the parts.)

[Canadian1968]

exactly.......... kinda of what i said at the very start of this thread

The aftermarket plain and simple is not any where close how the orginal oem was made. It's not that that sendING unit does not work or is not grounded . It simply is not desineed / calibrated correctly for the b body gas tank .

The thread mentioned before https://www.forbbodiesonly.com/moparforum/threads/yet-another-fuel-gauge-thread-but-different.124786/

its a bit of reading but explains alot .

[oldchevelle541]

Received a reply from the company in Willoughby Ohio who rebuilds the original units. $175.00 to rebuild plus the ride. I will hang on to original and consider the service if my frustration with aftermarket continues. This is a company to keep in your files. They were quick to respond.

[A383Wing]

Received a reply from the company in Willoughby Ohio who rebuilds the original units. $175.00 to rebuild plus the ride. I will hang on to original and consider the service if my frustration with aftermarket continues. This is a company to keep in your files. They were quick to respond.

they are also quick turnaround time also....I have used them twice now

Bryan

[oldchevelle541]

okay - level of frustration starting to set in.

Purchased OEM grounding strap from Year One and got it installed correctly. Tight and connecting output line from sending unit to gas line on other side of rubber gas line. Gauge moves about 3/16" when key is turned on butwill not go past "E". Grounded tank to chassis - no change. Grounded sending unit to chassis in addition to Year One ground - no change. Under hold I noticed my negative battery cable is not grounded to radiator support so I used an alligator clip wire from post terminal to bolt on rad support - no change. Even though not the correct gauge I was looking for some added movement of the needle. Went back under car and with my new multimeter and re-measured OHMs on the new sending unit. Meter read 40 Ohms very quickly.

so what next ?

[70sixpkrt]

http://www.kramerauto.com

I bought mine from them about 3 years ago and it is still accurate. A buddy of mine bought one last year and it reads accurate still. They check the calibration and recalibrate it before they ship them out. Before I bought one from KramerAuto, I went thru 3 other vendors and none of them worked.

[Nacho-RT74]

40 ohms takes to a good sender. Its between the range maybe ready to give you in between 1/2 or 1/3 of the gauge reading? dunno

have you grounded the BLUE WIRE of the sender ? it should give you FULL reading on gauge. Disconect the plug and ground it!

[oldchevelle541]

Thanks for the question - yes I did ground it originally before I purchased the sender. I used an alligator clip wire to sender post and the other end to chassis turned the key and needle went to full. That was suggesting to me wire and gauge in dash was good. Negative battery cable does not have aux lead ground but video I have of car before leaving owner showed gauge working plus I see so many mopars on ebay without the aux ground wire and I bet their gauges work. I also learned that if your temp and oil pressure gauge work it should not be a cluster limiter or volt regulator in the dash. Since new sending is stainless do you think it grounds differently or does not ground the same as oem unit ?

[Nacho-RT74]

yeap is true, if any of the gauges work, problem is not on voltage limiter. Maybe gauge calibration itself, some pin loosen at PCB, wire broken between sender and cluster, but definitelly not the limiter.

but it's weird having 40 ohms and needle barelly moving.

SS vs OEM sender ?... well, I can't tell it. Stainless steel have a diff electrical coeficient transmission than regular steel, but is not something to worry. No like this at least

I think original sender is fixable, with some soldering gun and lead, overlaping the copper tab... or using an intermediate copper section between both. Just will need to readjust the angle between point and rheostat. It worths the try.

I already had tried being I'm overseas LOL. As somebody told somewhere... I allways have to think out of the box to fix my stuff on car because just the shipping kills me.

I in fact had a similar problem with my sender, but the tab got completelly loosed from the floater shaft, and lead doesn't hold the same between both materials, hence the reason they are electricaly welded, so never could get a nice fix. BUT I can see you can still get solded copper over copper with lead

[oldchevelle541]

Gents,
in addition to my comment above I want to disconnect lead wire to sending unit and if I am not mistaken should measure about 5 volts when key is turned on. This should also confirm limiter is in good order. If correct how do I connect wires from multimeter ? Red goes to end of dark blue wire but where do you suggest I hook up end of black ground wire ?  Chassis or sending unit ?

[oldchevelle541]

Yesterday I spent a good amount of time retracing my steps and I have decided to back away for awhile.
- pulled lead wire on sending unit and grounded it to chassis. Gauge needle went to full, check
- attached low voltage tester to lead wire, showed voltage going through but light was flashing not steady, not sure what this meant.
- attached multimeter to lead wire hoping to see about 5 volts. Meter would not steady out. May have not hooked it up correctly.
- attached new OEM ground at sending unit output to steel gas line other side of rubber hose.
- attached ground from gas tank to chassis
- installed new ground from negative battery post to radiator support. I see so many 1970 B Body Mopars with and without this aux ground.
- made other attempts to ground sending unit in different ways
- pulled kick panel under dash and did an inspection. Nothing looked out of sorts.
- as is when key turned on gauge needle moves 1/8" then stops
- all other gauges including temp works suggesting no problem with circuit board and regulator/limitator.

Although I am getting ohms reading out of the new sending unit I am beginning to think it and the original factory gauge are just not working together. It worked before car was delivered.

Like the old Model T's I will use a wooden stick to measure gas levels in the tank - more reliable. LOL.

[Nacho-RT74]

the voltage limiter is not a steady 5 volts reading, but pulsating signal which makes a 5 volts average. If you used a digital VOM won't get a clear reading. It can just tested by analog devices, analog VOM or test light, both going in and out at some speed rate.

( good one on the Model T gas tank check LOL )

hipothetically, check voltage on the gas sender lead agains ground doesn't work like that but just if there is some resistance failure around... check this vid

https://youtu.be/qdaOSiScEu8

however being the voltage limiter a pulsating signal I think will be a more complex reading to analize, specially being there is load being used on the rest of gauges ( after check the vid, will understand this statement ).

why don't try to check the sender out of the tank ?... ground it with a wire and conect it to the sender lead... move the floater.

or on the bench with the VOM on Ohms.

[b5blue]

The connector pins on the printed circuit board for gauges is a known possible trouble spot. I soldered the base of the pins to the board VERY carefully.     

[jlatessa]

B5 has it right, be careful the solder does not hang down under the board,
it can short out against something, but I can't remember what.
It's been a long time and old age has had it's toll!

Joe

[oldchevelle541]

Thanks all will check your comments out.  BTW I did try to look up behind the dash and looks pretty original, does not look like anyone has been in there. I am considering getting my original sending unit rebuilt. Wouldn't that be a hoot to plug that one back in after rebuilding and it works.

[Nacho-RT74]

even B5 has it right, gauge, wiring, plugs and terminals are checking good when grounding the fuel sender wire, so I seriouslly doubt that is the problem and I THINK there is something weird about the sender. thats why I would test it out of the tank

[oldchevelle541]

Just got my new gas gauge LOL. No wires, ground cables, or anything.

[oldchevelle541]

just watched video suggested by Nacho - good stuff. Will check reading on each side of sender. I have new ground on other side of sender and if I measure any volts then we have localized problem. Still thinking I am leaning towards junking that new Classic Industries sender.

[Nacho-RT74]

being a pulsating signal and limiter still getting load on the other gauges can't tell if you get some easy to read signal at VOM reading voltage. Even less being a digital VOM ( in this case )

Just got my new gas gauge LOL. No wires, ground cables, or anything.

LOL

[A383Wing]

just watched video suggested by Nacho - good stuff. Will check reading on each side of sender. I have new ground on other side of sender and if I measure any volts then we have localized problem. Still thinking I am leaning towards junking that new Classic Industries sender.

we tried three senders from them, every one was junk

Bryan

[oldchevelle541]

Tried to test for voltage and grounds again tonight - still cannot find anything abnormal or obvious. The factory original is getting boxed up and sent out tomorrow to be refurbished. If I don't need it I will keep it for the other '70 Mopar we have in the family which still has it's original. Never know when they go. 

[oldchevelle541]

To all,
will let you know how we make out but I wish to extend my sincere appreciation for all the helpful comments. I got rid of a 2016 Dodge Challenger R/T 392 for this Coronet because you can't work on the new ones. I like old cars that have character and personality but this problem has me stumped.

[Canadian1968]

Alright you have done a lot . You really have narrowed it down.  You are getting 40 ohms off the peg of the sending unit correct ? This should give a reading 1/4 tank on your factory gauge (give or take ). The fact that gauge is barely moving tells me your gauge is getting a lot more resistance . Possible sources are your signal wire from the tank up to the back of your dash cluster . From there is goes threw a pin on your dash circuit board and routed to your gauge . You have already told us other gauges are working fine BUT that does not mean the circuit for gas is not damaged some how.  You said if your ground the sending wire back at the gas tank that it moves the needle ?  Did you actually let it get to full? Or did you jist see that it moves and pull it off. 

I would try this quick test again. And look for 2 things . Does the needle seem to hang up or stall anywhere threw the.sweep and does it go all the way to full . But do becarful once you see its to full remove the group  you can burn oUT the gauge if left on to long.

If it does not go all the way to full you can looking for the unwanted resistance in the circuit .  If it hangs up you may have to disassemble and see if your can repair the gauge .

[oldchevelle541]

Good information, when I grounded the lead wire the gauge needle responded by going towards full. I let it go 3/4 way so I would not create any damage. It did not jump, hesitate or other. Seemed to be a smooth steady motion. My factory gauge is en-route to Ohio for a rebuild. Will hook that up as soon as I get it back. If gauge responds I will get it transferred to the tank and we are back in business. If it does not will keep as a spare for the 70 Roadrunner which still has it's original sender.   

[oldchevelle541]

Folks,
just received my original sending unit back from John Wolf and Company in Ohio. $165 refurbished. A lot of money but if it fixes my long standing problem then all worth it.

Mark who works there is great. Bench testing it this evening Ohm reading goes from 11.8 to 78.8 so that looked good. I hook it up to the car without actually installing it and yes gauge now works.    But when I set the float to the full limit tab the gauge reads 3/4 tank. When I set float to half way point by eyeball gauge reads "E"  empty. Can someone tell me if this sounds legit or will it behave differently when in the tank. It is original gauge to the car but I had not owned the car when gauge was working hence cant say at the time it was accurate. Did not want to bend float rod  because the solder at the connection to the main shaft looks fragile.

[Canadian1968]

Your gauge needs to be recalibrated then .

If you put the unit to full, which as you said should be 11.8 ohms your gauge should be very close to full mark . Doesn't matter if it's in the tank or not

[oldchevelle541]

Thanks, after a long journey I put the original unit back into the car. Tank was near empty and I filled it up half way afterwards. Gauge reads 3/8 tank. That's good enough for me now since if gauge ever went to E I know I have a few gallons in there. Not going to remove gauge. It's never been out of the car and even though for some reason it is not accurate it at least works and tells me I have gas in the tank.

[Nacho-RT74]

I have to admit, being not in person to check anything I can think off, I'm pretty lost on this.

( I don't think an untoched gauge will miss the calibration by itself... not by that much at least!!! )