Fuel gauge finally works, but only briefly

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insidegroove

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i finally got around to replacing my sending unit today. once it was installed i turned the key on and was thrilled to see the needle move up to quarter of a tank.......then it slowly went back down to where it always was (below empty). every time i turn the key on the needle comes back up, but then the same thing....it goes back down. anyone know what would cause this?
 
What does the temp guage do?

How much fuel is in the tank?

What sender did you buy?
 
Dana67Dart said:
Yes but all A bodies work on the same electro mechanical principals so it is ALMOST moot
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I'm not sure I'd go quite THAT far. For instance, HOW they get that signal is pretty say from a 64 model like mine, to a last year of production 76 model. So there could be some different variables going on for sure.
 
I don't know RRR



there is a rehostat in the gas tank that varies the resistance to ground

There is a wire to carry that resistance to the guage

The guage has a heater that changes temperature with a change in the resistance of the rehostat.

That change in temperature bends a bimetal strip that makes the needle move.

The IVR lowers the voltage for the heater in the guage.

Are your gauges on your 64 straight electrical, does the fuel gauge move wildly as the fuel sloshes in the tank?
 
Dana67Dart said:
I don't know RRR



there is a rehostat in the gas tank that varies the resistance to ground

There is a wire to carry that resistance to the guage

The guage has a heater that changes temperature with a change in the resistance of the rehostat.

That change in temperature bends a bimetal strip that makes the needle move.

The IVR lowers the voltage for the heater in the guage.

Are your gauges on your 64 straight electrical, does the fuel gauge move wildly as the fuel sloshes in the tank?
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No, they are as factory with the IVR inside the fuel gauge. The later models have an external IVR that plugs into the back of the cluster. I am unfamiliar with say, 73 and up, but I suspect they are similar. My 75 F250 has one that bolts to the back of the cluster.
 
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Golden Star. Never heard of them. Here's their web site.
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Fuel sending units are one of the areas Mopar guys are having great difficulty. IMO, a genuine Spectra is about the best you can get "other" than NOS, or a remanufactured original. Spectra is made in Canada at least in North America. I've used lots of them through the years on my cars and customer cars and never had any complaints. Although some here say they are inaccurate, I've not witnessed that. I see no mention on the Golden Star web site of where their sending units are made. I could have missed it. I didn't inspect it with a magnifying glass.
 
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RustyRatRod said:
I'm not sure I'd go quite THAT far. For instance, HOW they get that signal is pretty say from a 64 model like mine, to a last year of production 76 model. So there could be some different variables going on for sure.
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There was a change in the resistance and marking points on the gage that Redfish has mentioned.
And we know they changed the fuel gage part number. The early ones have the long pickup tube and long float arm.

edit Redfish on resistance in gage units
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I have my dash apart on my 68 barracuda I am testing for continuity between circuits on the PCB. I have hooked an alligator clip up to the positive on the oil pressure gauge and then grounded the pins leading to the negative of each gauge oil, temp, fuel. The temp and fuel gauge sweep but the...
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Principle of operation should be about the same.
Bet its not terribly accurate but poke around the b-body forum and moparts to see if thats a common problem like it is with the A-body senders.

Anyway.
It sounds like its losing connection to the sending unit or the sending unit to ground.
Another possibility is the something in the feed line is opening. There no fuse so it could be the IVR opens and doesn't shut???

Set up each gage with a reostat or a set of resistors. About 11 ohms, 23 ohms and 70 something ohms if I recall correctly.
If I recall correctly your car had a standard instrument panel. So only two gages. Temperature and Fuel.
Test each gage to see if it works when connected to the resistors. If the gage works, the problem is downstream.
Makes sure neither wire to the sending unit touches ground.

edit: Make your own gage tester
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I went through something like this last year and it turned out that the float had gas inside of it although no hole could be found. The sender was new but the float was very thin walled so I replaced the float with one for a Mustang which had a thick wall. Problem solved. One other thing to watch out for is the float hanging up on the fuel pickup tube not allowing the float to rise past the tube. That was another problem that I encountered when resolving a fuel gauge issue.
 
Dana67Dart said:
They are. The amp meter changed some where in there from a pass through to a remote sensing with an external shunt.
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Yeah, like Del has tried many times to explain that to my stupid *** and I just cannot grasp it. LOL I know my limitations. LMAO
 
mcodecuda said:
I went through something like this last year and it turned out that the float had gas inside of it although no hole could be found. The sender was new but the float was very thin walled so I replaced the float with one for a Mustang which had a thick wall. Problem solved. One other thing to watch out for is the float hanging up on the fuel pickup tube not allowing the float to rise past the tube. That was another problem that I encountered when resolving a fuel gauge issue.
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That is a common problem too. We're stuck with really crappy parts for the most part. It sucks.
 
insidegroove said:
There's 6 gallons of fuel in the tank (18 gallon tank)
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My bet is 6 gallons in an 18 gallon tank with the aftermarket sender and their inaccurate results its working fine.

I have tried 2 aftermarket senders and both read empty for the last 1/3 to 1/4 tank.

The fact that the gauge is rising is a normal part of thermo gauges and might indicate yours is functional. the IVR provides full battery voltage for a few seconds at startup to get the gauge and the IVR ready to work. once the thermo aspect of the IVR is working it will start turning on and off like a flasher unit providing the needed ABOUT 5-6 volts ( in this case a square wave). Real Time engineering MOPAR Products actually simulates this with their full electrical IVR.

If you want to see this in action, get an OEM IVR or the RT IVR and attach a small lamp to the output. when you first attach 12V to the input the lamp stays on full then after a few seconds starts flashing
 
Product Review: A100 Fuel Sender For 67 Dart
This is real world testing

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