fuel gauge problems

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mopar410

mopar410

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I have a couple questions
(1)when I had the dash part I tested all the gauges with a 9v battery and all tested fine.Being careful to not hold the power to the gauge very long so not to burn it up.Now the dash is in the car and the fuel gauge doesn't register anything,needle sits way down below empty.So I gound the wire going into the tank and turn the key on,nothing registers.Then I ohm the sending unit and it is pretty much ground out as it sits.I then rechecked the fuel gauge with a 9v battery and at first it would rise slowly and at just under empty it skipped and dropped a little then rose again but never passed that point.After a few trys it seems to not move much at all now.I didn't hold the battery to it more than 15-20 seconds at most each time and the key was off.I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster.
How can I test the sending unit better or do I need to pull it out,the ground strap is in place so I would like to figure this out before I have to mess with all that.
(2)Anyone know the wire color that goes to the temp sending unit.mine was cut by the PO and tape from one end to the other.Any input is appreciated.

Also if I need a new gauge and unit where is a good place to get them.
 
Thats not what I was hoping to hear lol.Any ideas what would have caused it,the sending unit shouldn't have caused it,right?I dont recall the gauge ever moving while the key was on.
 
Only way to tell for sure is to rig up a test circuit, one way to do that is to yank the cluster and unscrew the stud nuts on the gauges. Pull the VR for certain. This will isolate the gauge studs from everything, and you can hook clip leads to 'em.

If you then wire the two gauges in series, and hook to an power supply you can vary (AA cells, in series, etc) the two should read the same

That is, power supply + to temp gauge + ----- temp gauge sender terminal to fuel gauge + ---- fuel gauge sender terminal back to power supply neg.

So if the gauge you think is good reads 1/2, so should the second.

Here's some photos, 3V battery, first the gauges in series, then the two gauges in parallel. You can see that they read substantially the same, proving that either both are fairly accurate, or both are fairly off by the same amount
 

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Ok thanks that is a good idea.it will atleast show where the gauges are in relationship to each other.I will try it and see what I come up with.
 
""Then I ohm the sending unit and it is pretty much ground out as it sits. ""
Ohm meter doesn't say "pretty much dround out" , not one that I've seen anyway.
Ohm reading at the sender should be somewhere between 10 ohms and 73 ohms per how much fuel is in the tank. Sender wire should show the same behind the cluster also. If not that current path is flawed.

""I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster."" I'm totally buffaloed by that statement. You may have created your problem there.

Temp sender wire is purple.

Good luck with it
 
RedFish said:
""Then I ohm the sending unit and it is pretty much ground out as it sits. ""
Ohm meter doesn't say "pretty much dround out" , not one that I've seen anyway.
Ohm reading at the sender should be somewhere between 10 ohms and 73 ohms per how much fuel is in the tank. Sender wire should show the same behind the cluster also. If not that current path is flawed.

""I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster."" I'm totally buffaloed by that statement. You may have created your problem there.

Temp sender wire is purple.

Good luck with it
Click to expand...
Thats a good idea measuring the ohms at the guage end to compare it with the ohms at the sender.What i meant by"Then I ohm the sending unit and it is pretty much ground out as it sits. "I ohmed the sender off the tank strap bolt and then checked the ohms from that bolt to the other strap bolt and the readings were close to the same.I was useing a needle type reader set on x10 and it read about 6 on the sender and 5 on bolt to bolt.Also the tank is empty.
"I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster."It was late when I posted this and I couldn't remember what they were called but its a solid state resistorwith a built in fail safe like the ones you offer.Actaully I seen yours after I bought mine.
Thanks for the temp wire color also.
 
mopar410 said:
Thats a good idea measuring the ohms at the guage end to compare it with the ohms at the sender.What i meant by"Then I ohm the sending unit and it is pretty much ground out as it sits. "I ohmed the sender off the tank strap bolt and then checked the ohms from that bolt to the other strap bolt and the readings were close to the same.I was useing a needle type reader set on x10 and it read about 6 on the sender and 5 on bolt to bolt.Also the tank is empty.
"I do have a electronic resistor that is installed and is suppose to shut down if too much power is going to the cluster."It was late when I posted this and I couldn't remember what they were called but its a solid state resistorwith a built in fail safe like the ones you offer.Actaully I seen yours after I bought mine.
Thanks for the temp wire color also.
Click to expand...


Ohms test should be from the senders wire terminal to any chassis ground.
 
I think when you say "I ohm out the sending unit" you really mean you checked the resistance of the sending unit (a variable resistor) with an ohm meter. Resistance is measured in ohms, voltage is measured in volts and current is measured in amperes or amps.
 
In the event that I do have to get the sending unit and the fuel gauge(I'm sure I will).Where is a good place to get them.I found this at summit and it states it works with the old gauges.
http://www.summitracing.com/parts/RSD-YSU6301/
Or should I be looking for a combo or package from the same company to ensure a proper reading?
 
Sorry to thread jump, no highjacking intended. But I have the exact same issue, my gauge has been working but sort of intermittenly but the other day I put $20 in and I had more fuel than its had since I owned it and was glad to see the gauge go just past half tank, the next morning nothing and it hasnt moved since, I can see one big purple wire coming from the tank in the trunk, is the ground supposed to come from there as well? Its my understanding sometimes in these old cars the gauge in the tank itself can get gummed up and stuck? I'll tinker with wires and see what happens but any ideas are helpful.
 
mopar410, you need to tell us what model and year your car is and whether you have a tachometer (Rallye dash). Early cars had a Vreg inside the fuel gage. What is this "electronic resistor" you talk of. Posting photos would help you a lot. I am guessing an electronic Vreg, but no need to guess.

Outkast. The ground for the fuel sender is the body of the sender. There should be a factory clip that connects the two metal tubes across the rubber hose. Clean it and add a ground wire w/ hose clamp if needed. After that, ground the sender wire and see if your gage goes to max. To go further (calibration), you need to measure the resistance signal of the sender and substitution resistors to check the gage.

For anyone getting a new sender, think long term. A 3/8" outlet might be better. One with a return line is needed for EFI. All exist and fairly cheap from $38 to $55. See ebay and Summit Racing.
 
BillGrissom said:
mopar410, you need to tell us what model and year your car is and whether you have a tachometer (Rallye dash). Early cars had a Vreg inside the fuel gage. What is this "electronic resistor" you talk of. Posting photos would help you a lot. I am guessing an electronic Vreg, but no need to guess.

For anyone getting a new sender, think long term. A 3/8" outlet might be better. One with a return line is needed for EFI. All exist and fairly cheap from $38 to $55. See ebay and Summit Racing.
Click to expand...

yeah it was getting late and I was tired.Its a factory 318(reg dash)70 dart,no factory tach.It is a regulator not a resistor.The reason i mentioned the one from summit is I heard people getting new senders and the calibration being way off.the summit one says it works with the old gauge but I've never had to buy one so I didn't know if it was a good brand or if it had a bad reputation.
 
Well crap! I think I found the problem, I just went on lunch and put 10 bucks in and I think the solution maybe get a garage or the cheaper rout and get a locking gas cap unless somthing is hit and miss.
:wack:
 
Just took the sender out and wouldn't you know it the float popped off inside the tank(fairwell little buddy).The board that the wire wraps around was broken and unrepairable.By the looks of the crud and the tank and outter sender it is the original.The guage is still in the car and it still only goes up the empty with a 9v battery which is odd because to get any movement it has to be a complete circle of wire,maybe a rough spot that it cant cross.My next step is to check for bad wire connections,just trying to get some kind of movement from grounding the sender unit wire.I hate chasing wires.
 
Update.After a few hours chasing wires I came up with the gauge is still working but the nuts holding the gauge on lost its connection so I sanded the copper surface and the nut surface and the hole for the bolt.Reinstalled the nuts and everything is working.My purple temp gauge wire is cut at the back of the engine but not a big issue just run some wire and that should be working also.The six pack intake doesn't have a port for a after market temp gauge.the annoying thing is back over the winter I sanded the instrument cluster and had everything working.So I guess it glazed over while sitting in my climate controlled basement.
Now I seem to have no dash lights or blinkers](*,)](*,)](*,)](*,)](*,)](*,)
 
On my project none of those lights were working either, so I spent almost $40 on bulbs and cleaned every contact point I could get too and used that blinker grease to lube every bulb and connection and so far so good even the funny little front fender blinkers are working, vasaline works well also for bulbs to prevent humidity on the contacts.
 
Outkast said:
On my project none of those lights were working either, so I spent almost $40 on bulbs and cleaned every contact point I could get too and used that blinker grease to lube every bulb and connection and so far so good even the funny little front fender blinkers are working, vasaline works well also for bulbs to prevent humidity on the contacts.
Click to expand...
Before I disassemble the car all the exterior lights worked so I think there is a loose wire somewhere or a bad connection.Possibly a bad ground somewhere as the blinker flasher is not working either.
 
Another update.I found my blinker flasher had a wire pulled out of it so I put it back together and the blinkers work and I also removed the headlight switch to find the coil spring that works the dimmer was broken and that was causing the dash light to not work.But my gauge is till not working,reading with 22.8 on the ohm meter to the sender.The hand just throbs ever so slightly but doen't rise but maybe 1/32.I need to get it to the gas station to fill it up and see what it does then.I did have an idea for a temp or long term work around.At some point between the gauge and sender splicing in a wire that can be stored out of sight and when you want to check your fuel just take your ohm meter and see where it ohms at and you know(after trial and error) how much fuel you have.With the switch off seems to be more accurate as it would be reading just the sender with no other parts to contaminate the signal.I need a new gauge as I think this one is roughed up and the needle hangs up inside it.So untill I get it fixed right I think this will work for now.
 
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