Fuel Gauge Problem

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Boogercj7

Boogercj7

Mopar Boot
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Dec 13, 2010
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Location
Jacksonville, NC
I just installed a new fuel sending unit in my 72 Dart Swinger. Now that I have it on the road, the gauge seems to work, however, when the gauge reads empty, I can only put 6 to 7 gallons of gas in the tank. I have already checked the ground on the sending unit and it didn't make a difference. Just wanted to know if anyone else has seen this before I pull the sending unit to check for the correct resistance.
 
All of the other gauges work fine. The fuel gauge works too, just that it shows empty after using only 6 or 7 gallons.
 
I have to guess the problem is in the gauge. There is a bimetal strip inside that bows to move the needle. It should return to straight as an arrow at room temperature. If it has been overheated resulting in a perminant bow, the geometry or relation of the moving parts gets screwed up. Installing used gauges is a hit and miss / ganble at best.
If the 73 fuel gauge is the same , I have a known good one here or I can repair yours. Good luck
 
There is a certain amount of adjustment that can be made to the gauge and sender. You have to remove them from the car to do it however. I like to have them both on the bench and use jumper wires to connect them as I make the adjustments but you could start with just pulling the sender to see if you can get full range by tweaking some of the limit tabs. Just make sure the float doesn't rub on the bottom or top of the tank as it will wear a hole in it in short order. Some of the replacement senders these days have a different resistance than the factory original one did. And as RedFish mentioned, years of heating and cooling can change the curve of the bi-metal strip in the gauge and therefore it's accuracy. Throw in 40 year old wiring, circuit board, and voltage limiter and it could read anything!
 
Thanks for the help guys. I am getting ready to move, once again, and once I get settled I am going to tackle this. The first thing I am going to do is remove the sending unit and check the resistance. I just hate cruising around not knowing how much gas I actually have in the tank.
 
I have the exact same problem, and my garage guys have yet to solve it.
The sending unit is about nine (9) months old and came from YearOne.
 
Why would you need to remove the sender to measure the resistance? Next time you have it at a know volume (after fill up or down x gals and you will know x after you fill up), check the resistance. I recall the wire goes thru the "body connector" in the left kick panel (by driver's left foot). You can disconnect to measure it there. The wire also goes thru the trunk, but my 65 doesn't have a connector in the trunk. You could cut the wire and install a bullet connector, but best to not molest it. Otherwise, you could remove the circular connector on the dash to access the wire, but I hate working behind the dash. Even if you have to back onto ramps and check right at the sender, that is much easier than removing the sender.
 
At full tank the sender should show no less than 9.6 ohms. Empty is 73 to 78 ohms.
If the sender works properly 1/2 tank is 23 ohms.
Since the internal parts of the gauge have been respoding to heat created by the resistance, countless hours of toasting at full has taken its toll.
What was once a pale yellowish silk insulation on a nichrome wire winding often appears 3 or more times its original diameter. Caked with black, crunchy, nastiness. I suspect the worst examples I have seen was the result of smoking in the car. Anyway, it can't be cleaned and it does effect the needle responce.
Here's atip, If you remove the gauge , look first at the vent hole behind the top of the screen. If there is a yellowish or brwnish stain there you'll have an idea what to expect the inside to look like. Not good :(
Too much info ? Sorry just trying to shed light on why a new sender doesn't aways solve the problem. Hope this helps
 
I have the same problem in my 72 Swinger that I just bought. The guage shows empty way before it is empty. I guess that's better the the opposite. My car has a new sending unit and new gas tank. Could the new sender be improperly installed in some way?
Thanks,
Frank
 
RedFish said:
Nope a locating tang prevents installing wrong and or rotating the sender when the lock ring is rotated.
Click to expand...


I see. So I may have a bad guage then. I do have the solid state voltage limiter for the guages, but haven't installed it yet. I'll try that and if I still have a problem, maybe a new guage will be in order. Thanks for the help.
Frank
 
csx452 said:
I see. So I may have a bad guage then. I do have the solid state voltage limiter for the guages, but haven't installed it yet. I'll try that and if I still have a problem, maybe a new guage will be in order. Thanks for the help.
Frank
Click to expand...

Here's one thing you might try. Replace the gauge sender with a resistor (you should be able to get them at Radio Shack) You need a big wattage wire wound resistor, and probably don't want to hook it up longer than it takes to check the gauge.

According to the info I have

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

Those resistances don't have to be "that close" Fer 'xample, anything from 70-75 should give you pretty close to MT

Another thing you can do with clip leads is to

1 disconnect the temp sender wire and make sure it is not grounding out, temporarily leave it hang.

2 remove both nuts from the gas gauge unit, this will disconnect the gas gauge from the circuit

3 use a clip lead and jumper the fuel tank sender wire connection (at the cluster) over to the TEMP sender wire. This will turn the temp sender into a "gas gauge" and you can see if they read the same.

This might give you a clue as to whether the gauge is correct / not or the sender is wrong.

My usual rant on cluster problems:

1 Power to the cluster connector pins, due to broken/ corroded pins

2 Problems with the voltage limiter

3 Problems on the PC board, including bad connections at the limiter, corroded nuts at the gauge units, and bad pins again on the cluster connector going out to the sender(s)

4 Poor ground at the cluster. work/ tighten/ loosen all the ground screws holding the board down, and attach a separate ground wire, bolted securely to the dash brace behind the panel, leaving enough slack to get the dash in/ out

On my own 67, the "socket" (springy brass fingers) for the limiter was not really making connection to the board, I had to jumper solder connections across from the brass to the copper board. The nuts were loose / corroded on both gauges, and several of the cluster connector pins were damaged. I replaced the connectors with "Molex" style from Radio Shack
 
More good advice here. My car does have a smelly interior from the rubber mat getting wet from below due to 2 holes in the floor pan. I'm thinking now that if it was really wet inside that corrosion may be a problem on the connections. Time to pull the guage cluster and have a look see.
Thanks,
Frank
 
A quick check for all guages oil, temp, and fuel, is to take one or two aa or aaa batteries and connect them to the respective terminals on the guages. One battery should result in approximately 1/4 needle deflection and two batteries hooked in series (like in a flashlight) should give about half scale deflection. The voltage regulator for the instruments provides about 5 volts to the instruments.
 
#1 Solid state regulator on your guages. MA covered one eons ago, or you can buy them now.

#2. Check resistance at the sender, sender installed.

#3. Check resistance all along the sender wire. Resistance is resistance and it doesn't matter if it occurs at the sender or at that break in your 40 year old insulation.

#4. Mine, and obviously many others, have the same Year One origins and similar issues. I think I just need to bend the float arm if the resistance checks OK. This was not an issue prior to the new 3/8" sender, so I highly doubt that the needle is warped. I'd say it's rooted more in the cheapass parts from China that are infiltrating our hobby.

#5. Motorcycles don't have fuel gauges, Mopars don't typically have tripmeters or reserves, so you get to split the difference.
a.)Toss a 2 1/2 gallon fuel can in your trunk. Go fill up your gas tank AND fill the 2.5 gallon gas can in your trunk.
b.)Write down your odometer reading. Go for a drive. Mix it up, city n' highway. Try to make it a NORMAL drive for the way you drive, but go until you're out of gas. Literally...side of the road, stalled. (This is where your gas can in the trunk should come in handy, but first....)
c.)Make note of your vehicle mileage. This is your "range". Knock 30 miles off that, and write/memorize/record your mileage at each fill-up. Getting close to your range? Time to fill up!
 
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