fuel sending unit and fuel gauge trouble

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70dart65coronet

70dart65coronet

mopar or nocar
Joined
Jan 2, 2013
Messages
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Hello All,

When i bought this 1970 dodge dart, they had removed the factory fuel tank and put a small fuel cell in the back with no fuel sending unit.

I put a larger fuel cell in with a sending unit.

https://www.summitracing.com/parts/jzp-251-012-01

I hooked up the factory sending unit wire to sending unit, and the other lead to ground, and i get nothing on gauge

Any ideas? Does anyone have a wiring diagram?

I have checked all the obvious things.

Thanks

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I can tell you this much.
Maybe the fuel gauge isn't working. With the ignition key on, briefly touch the fuel sending unit wire (the wire that plugs into the sending unit on the gas tank) to a good ground. Have a helper tell you if the gas gauge needle moves. it should. If not, try holding the wire to the ground a little longer. Also, with a volt meter, you should have a reading of about 5 volts at the fuel sending unit wire. If there is no current in the wire, and the needle did not move when the wire was grounded, you can next check for current at the back of the gas gauge. If there IS current going through the gas gauge, and none going out, the gauge is likely bad. If there is NO current flowing through the gas gauge, the IVR (instrument voltage regulator is likely bad. On a 69 Barracuda, the IVR is built into the gas gauge, and the gas gauge will have 3 terminals on the back: One terminal for 12 volts into the IVR, one terminal for 5 volts that will flow through the gas gauge (and that 5 volts also flows to one of the two terminals on the back of the oil and temp gauges), and one terminal for the current flowing back to the fuel sending unit wire. If your gas gauge only has two terminals on it (not sure when that happened), the IVR is not in the gas gauge, and is easier to replace. Also, if the IVR is bad, the oil and temp gauges will not work, but if they are working, your IVR is likely OK.
Your gas, oil and temp gauges all have a bi-metal filament in them similar to what is found in your home's thermostat. When current flows through that filament, it heats up and moves, causing the needle to move. The more current that flows through the filament, the more movement you get. The current flows through the gauge and through a wire all the way back to the fuel sending unit. First understand that the fuel tank MUST be well grounded! The fuel sending unit contains a rheostat that allows the current to flow from the gauge to the car's ground. With a full tank of gas, the sending unit's float goes all the way up, and the rheostat lets a lot of current flow through to the ground. Since you now have a lot of current flowing through the fuel sending unit (and, consequently, through the fuel gauge) you get a lot of movement in the needle, and it tells you your tank is full. If, however, there is no gas in the tank, the float is all the way down, the rheostat is not allowing any current flow through to the ground, there is no current flowing through the fuel gauge, and the needle will not move. So, the bottom line is that for your gauge to work with the fuel cell's sending unit, the sending unit must operate like your original (regulating the amount of current that flows through to the ground), and the resistance in the fuel cell's rheostat must be similar to what a 70 Mopar sending unit would be, and the fuel cell must be properly grounded. I am not saying you cant get your gauge to work with a fuel cell, but if all you are doing is hooking the fuel tank sending unit wire up to the fuel cell, this is likely why it isn't working.
 
harrisonm said:
I can tell you this much.
Maybe the fuel gauge isn't working. With the ignition key on, briefly touch the fuel sending unit wire (the wire that plugs into the sending unit on the gas tank) to a good ground. Have a helper tell you if the gas gauge needle moves. it should. If not, try holding the wire to the ground a little longer. Also, with a volt meter, you should have a reading of about 5 volts at the fuel sending unit wire. If there is no current in the wire, and the needle did not move when the wire was grounded, you can next check for current at the back of the gas gauge. If there IS current going through the gas gauge, and none going out, the gauge is likely bad. If there is NO current flowing through the gas gauge, the IVR (instrument voltage regulator is likely bad. On a 69 Barracuda, the IVR is built into the gas gauge, and the gas gauge will have 3 terminals on the back: One terminal for 12 volts into the IVR, one terminal for 5 volts that will flow through the gas gauge (and that 5 volts also flows to one of the two terminals on the back of the oil and temp gauges), and one terminal for the current flowing back to the fuel sending unit wire. If your gas gauge only has two terminals on it (not sure when that happened), the IVR is not in the gas gauge, and is easier to replace. Also, if the IVR is bad, the oil and temp gauges will not work, but if they are working, your IVR is likely OK.
Your gas, oil and temp gauges all have a bi-metal filament in them similar to what is found in your home's thermostat. When current flows through that filament, it heats up and moves, causing the needle to move. The more current that flows through the filament, the more movement you get. The current flows through the gauge and through a wire all the way back to the fuel sending unit. First understand that the fuel tank MUST be well grounded! The fuel sending unit contains a rheostat that allows the current to flow from the gauge to the car's ground. With a full tank of gas, the sending unit's float goes all the way up, and the rheostat lets a lot of current flow through to the ground. Since you now have a lot of current flowing through the fuel sending unit (and, consequently, through the fuel gauge) you get a lot of movement in the needle, and it tells you your tank is full. If, however, there is no gas in the tank, the float is all the way down, the rheostat is not allowing any current flow through to the ground, there is no current flowing through the fuel gauge, and the needle will not move. So, the bottom line is that for your gauge to work with the fuel cell's sending unit, the sending unit must operate like your original (regulating the amount of current that flows through to the ground), and the resistance in the fuel cell's rheostat must be similar to what a 70 Mopar sending unit would be, and the fuel cell must be properly grounded. I am not saying you cant get your gauge to work with a fuel cell, but if all you are doing is hooking the fuel tank sending unit wire up to the fuel cell, this is likely why it isn't working.
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I didn`t read all of the second posters advise. but, if u bought a fuel cell w/ sender in it, and didn`t specify it was for a Chrysler product, it will be a Chevrolet sender, which will not work w/ a mopar gauge. they are diff. ohms operation.
 
The link to aftermarket tank kit purchased shows a 70-10 ohms sender which is close enough to Chrysler OEM gauge.
Use a volt meter to check at the sender. You're looking for a pulse voltage 2.x, 3.x, averaging about 6 volts. If there's no voltage there you could check at the rear harness connector behind the left kick panel but... a fault there is extremely rare.
The temp gauge operates on the same pulse voltage. If it doesn't work either, the limiter that produces the pulse voltage is suspect. If the temp gauge does work just fine, The fuel gauge may be loosing connection where it attaches to the printed circuit board with pal nuts. This is a somewhat common fault.
Sure there are other possibilities, like broken connector pins on the circuit boards. Most of these inst' panels have been removed before for one reason or another and that's how the connector pins get broken. So... If your tests determine the panel must come out, be careful. Consider installing a new limiter, new light bulbs, every service practical, while its out.
 
halifaxhops said:
Repair Your Fuel Gauge
This should cover it all for you.
Click to expand...
That page can help but... There are errors within it.
First; The oil warning lamp does not ground at inst panel. Oil warning lamp and park brake lamp both ground through remote switches. These are the only 2 lamps in any model printed circuit board that require 2 wires.
Second; These gauges and senders operate on a 80->10 range. 80 = no needle movement. Approx' 73 ohms will bring the needle up from its home position to the empty hash mark. You can't break out the calculator and determine half the ohms ( 35 ) is half the gauge range. They don't work that way. As the ni-chrome wire inside the gauge heats up, its per inch ohms resistance changes. It's 13.4 inches of a 1.5 ohms per inch at 68 degrees wire. Heat changing the resistance, generates more heat. And I'm sure that goes over the head of the novice. Anyway... FACT approx' 23 ohms is half range. That author states 10 -> approx. 100 ohms and then assumes/states 50 ohms is half range. Totally wrong. I should stop there but... There are also gauges containing 13 inches of 1 ohm per inch wire ( varies with application ). So some gauges measure 20 ohms across while others measure only 13 ohms across. The same 23 ohms = half the range applies to all. Now I'll stop.
Just like "open the rallye fuel gauge and bend the little thingy" BS found online. Once its published, it can't be corrected. Or maybe it could be but just isn't. Only the author knows why. Good luck to all
 
RedFish said:
That page can help but... There are errors within it.
First; The oil warning lamp does not ground at inst panel. Oil warning lamp and park brake lamp both ground through remote switches. These are the only 2 lamps in any model printed circuit board that require 2 wires.
Second; These gauges and senders operate on a 80->10 range. 80 = no needle movement. Approx' 73 ohms will bring the needle up from its home position to the empty hash mark. You can't break out the calculator and determine half the ohms ( 35 ) is half the gauge range. They don't work that way. As the ni-chrome wire inside the gauge heats up, its per inch ohms resistance changes. It's 13.4 inches of a 1.5 ohms per inch at 68 degrees wire. Heat changing the resistance, generates more heat. And I'm sure that goes over the head of the novice. Anyway... FACT approx' 23 ohms is half range. That author states 10 -> approx. 100 ohms and then assumes/states 50 ohms is half range. Totally wrong. I should stop there but... There are also gauges containing 13 inches of 1 ohm per inch wire ( varies with application ). So some gauges measure 20 ohms across while others measure only 13 ohms across. The same 23 ohms = half the range applies to all. Now I'll stop.
Just like "open the rallye fuel gauge and bend the little thingy" BS found online. Once its published, it can't be corrected. Or maybe it could be but just isn't. Only the author knows why. Good luck to all
Click to expand...
reply is good info. I put a new 3/8 sending unit in my fish, using it as a return for the fuel inj. system. I cut the sock filter off, leaving the p/u as long as possible. then installed a new autometer gas gauge, w/ a new digital filter that's supposed to be 6 ohm output. I rewired the whole car w/ an EZ kit.the gauge still doesn`t work right. autometer says the gauge can be calibrated w/ an empty tank. guess I`ll have to wait on warm weather, I just filled up the last nice day we had. the gauge goes up to full and then settles back about 3/8 of a tank low, and goes down from there. all comments appreciated------bob
 
ok guys, i have a blue wire at the sending unit, its good all the way up to the dash. no volts at the sending unit. doesnt move the needle if i touch the blue wire to ground either. so it must be somewhere in the dash. i forgot how much a pain it is to get ic out, how should i trouble shoot the ic, remove it completely or just pull it out of the dash with the wires still connected? i gave up on it tonight, i got the speedo cable removed.
 
In a group this size you can get a wide range of responses. Some will get ( sort of sit ) upside down, others remove the front seat to be more comfortable while changing bulbs, limiters, etc.., from underneath the dash.
To remove the inst' panel and take it to a workbench is the proper method. The "how to" procedure is detailed in factory service manuals. Many of those are free downloads ( at Mymopar.com I think ).
Through a lot of experience I have modified their method a little to suit myself. No need to go into that though.
 
ok guys so i crawled under there with the flash light and looks like there are no wires hooked up to the fuel gauge or the temp gauge... i found a wiring diagram online...looks like a wire comes off the voltage limiter, goes to one side of the fuel guage, and the other side takes the blue wire that goes to the sender, that should be pretty basic to do?
 
70dart65coronet said:
ok guys so i crawled under there with the flash light and looks like there are no wires hooked up to the fuel gauge or the temp gauge... i found a wiring diagram online...looks like a wire comes off the voltage limiter, goes to one side of the fuel guage, and the other side takes the blue wire that goes to the sender, that should be pretty basic to do?
Click to expand...
you got a wiring diagram ?
 
70dart65coronet said:
ok guys so i crawled under there with the flash light and looks like there are no wires hooked up to the fuel gauge or the temp gauge... i found a wiring diagram online...looks like a wire comes off the voltage limiter, goes to one side of the fuel guage, and the other side takes the blue wire that goes to the sender, that should be pretty basic to do?
Click to expand...
Did I not mention printed circuit boards and their contact pins in a earlier post? Your wiring diagram show current paths. Maybe someone could post a photograph here for you. I don't have. Anyway.... The gauges do have threaded mounting posts and nuts. The only instrument in the a-body panel that has wires directly attached to its mounting studs is the amp/ALTERNATOR gauge. Printed circuit boards conduct current to everything else.
And by the way, although one of those 2 wires with ring terminal is a black, it isn't a chassis ground wire. Both red and black are unfused firecracker hot at all times.
 
yep, that drawing shows the harness connector attached to 5 pins on a circuit board. From there the current path is drawn in broken lines, as in not a actual wire. The paths on the board itself can look more like getting the rabbit to the Trix on the back of your cereal box. It's not tiny or complicated.
One test you could do is check for a pulsing voltage at the purple wire that was supposed to go to the OEM temp sender. That would check the limiter output. We already determined no pulse voltage through the fuel gauge but that doesn't fully suggest a failed limiter. No pulse voltage through either does bring limiter to higher suspect.
Beyond that, 2 suggestions, Disconnect the neg' battery cable, get in the floor, reach up in there with a 3/8 socket, and attempt to snug the nuts that mount/attach these 2 gauges to the circuit board. Dont overtighten!
OR
DL a service manual. Pull the instrument panel.
 
Oh and by the way, If that purple temp sender wire out there is or has been shorter to ground, That would kill a limiter and possibly damage/kill a fuel gauge at the same time.
 
Oki tested for pulse voltage...at first I had it, then I checked again it was gone, so I wiggled the IC and I got pulse voltage again. While having pulse voltage I took the blue wire at the sender and touched it to ground, I still couldn't get the fuel needle to move.
 
wiggling the inst' cluster to make pulse voltage come and go that far out the circuit doesn't help much. You have to have the 12 volts into the limiter, then pulse out of it, and into the fuel gauge, and through the fuel gauge and down that length of wire to your test point. Any loose connection in that path ( pull the inst' panel! ) Also know that a digital volts meter doesn't report the pulse accurately but... any meter can report voltage present that isn't enough to operate the whatever. In this case you need enough current to generate heat in a resistor/thermal range indicator.
A pal nut is stamped from tin. It has a inner edge touching a single thread in a contact post. Then a outer edge with nearly no flange sitting on a contact pad of the board. Imagine a stranded wire with all but one or two of it's strands broken. Meter will show voltage but..., Enough current passing to operate anything aint happening ( unless the wire was waaaaay oversized. 1 stand of a battery cable will operate a dome lamp LOL ). Anyway... A loose pal nut is the same broken wire condition.
Many owners here in this forum have found this very same fault, 2 within the past week. Others of us answer the same questions over and over.
I wont go into why engineers choose to use pal nuts at these locations but used machine nuts and toothed washers at the amp gauge.
The limiter could be loose in its contacts too but those are heavy gauge male spades in springy females that absorb vibration. Anything is possible, just some things less likely.
What we can assume at this point... the limiter can operate, the resistor winding inside the fuel gauge is intact. Conductors that are actual wire are probably ok.
 
Ok I got the IC out, looks like someone has been in here before...some of the pins are soldered and loose and broke...what's the best way to go about fixing these? What tests should I do after I get these pins fixed.

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Attempt repair or buy new? I can't advise there.
 
Ok I got the new printed circuit boards in there....and now it works! It reads at a half when it's full, not sure if it's coincidence or not but the tank is about half the size of stock...

Another odd thing that took me a bit to figure out is that the gray wire for oil pressure sender was removed from the firewall pass through connector.

I'm running a set of after market auxiliary gages, so now I will have the factory gages as a failsafe. What do you guys use for that oil pressure line, they provide a plastic line which I don't like...do they make a better option for that little line?

Also what are you guys using for transmission cooler lines? I want to get away from the rubber hoses.
 
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