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Fuel and Temp gauge

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irby445 View Drop Down
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    Posted: Dec/11/2017 at 9:38pm
Hello everyone,

I am new to the AMC world but my wife and i have bought a 1959 rambler super 4 dr.  i have read a lot about the fuel and temp gauges not working and have tired most everything to figure it out.   the voltage regulator is good that goes to both gauges, the wiring is good and has good connections everywhere.  On the fuel gauge side of things the sending unit looked pretty rough so i put in a new one but that didn't fix my problem.  Just wanting to kick ideas around and see what i can come up with on a direction on where to go now. Any suggestions would be appreciated. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Dec/11/2017 at 9:59pm
To test your fuel gauge disconnect the sender wire at the tank and connect it to a good clean ground on the chassis. The gauge should peg on full.    You can do the same thing with the temperature gauge by pulling the wire off of the sender and connecting it to a good ground on the car.   That will tell you if the gauges have the proper voltage going to them and that they are responding to the senders.  Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote irby445 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/12/2017 at 12:25pm
i have connected a ground to the fuel gauge and it didn't more at all which lead me to believe that the gauge is bad.  i check the regulator with a volt meter and i had 12 going in and around 5 coming back out. i have read that 5 is about normal for this style of regulator.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Dec/12/2017 at 12:57pm
If you already determined that the voltage regulator in the panel has power upstream and downstream of the unit itself, (you said before that the IVR was good) then the remaining two problems to check are: (1))make sure the fuel gauge has voltage and (2) make sure you have continuity in the wire from the sender to the gauge panel.  If you have continuity and the gauge is getting power, and still no joy, replace the gauge.  Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/14/2017 at 9:51am
You won't see 5V coming out of the IVR unless you have a voltmeter with a long sample and hold time. The IVR output switches between 12V and 0V. The duty cycle, time on/time off, determines the average output voltage of about 5V. The switching speed is about 1/2 second depending upon the amount of gas in tank and the engine temperature. Most voltmeters cannot give a stable reading at this frequency.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcenthusiast Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2017 at 9:35am
Back in late '80s my parents bought a new GM car and the gas gauge was always flaky. The dealership technicians failed to solve the problem. The net result cast a much larger shadow on the whole car; everyone hated the car because the fuel gauge wouldn't work right & the whole car was perceived to be 'trouble prone' because the 'stupid' gauge. (false conclusion because the rest of the car was basically maintenance free but nevertheless true; switching drivers nobody knew how much gas was in the car -this inevitably created the old 'oops I ran out gas scenario' and hatred for the car.

That experience in my life taught me a lesson: do whatever it takes to fix the fuel gauge in order to enjoy the car.

IMO, one muster enough determination, perseverance, patience and endurance to fix it in order to enjoy the car. So IMO, just make your mind up right now YOU will obtain mastery over the electrical circuits and the fuel gauge is going to work over your dead body/if that's the last thing you ever do/or die trying!

*This is even more important on an AMC car because they are already assumed to be inferior by lack of popularity (false conclusion/false statistic again but nevertheless true = that's what other people think/can't change their world view, status quo, ego, self esteem etc.)
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Apparently, you have the external voltage regulator type system.

It may be helpful to understand why it has a voltage regulator in the first place; this is because the whole car industry changed from 6 volt systems to 12 volt.

I'm not an electrical engineer but the basic understanding is this: 12 volt system allows more electrical accessories with smaller wires, then with the invention of an alternator and transitors the car's electrical system became smaller, more maintenance free and lighter (even though in some cases 6 volt system has an advantage by merit of flowing more amps. Eg: the starter motor, ignition circuit and... the gas and temp gauges -because they both use a long 'sensor wire' to the sending unit)

-this is basically why the ignition circuit uses a resistor wire and the gauges use a voltage regulator: even though the car's electrical system was 'upgraded' from 6 to a 12 volt system, the 6 older 6 volt design works better for the ignition and the gauges... so the electrical engineers kept it that way & used a resistor wire on the ignition and a voltage regulator on the gauges instead.

So, in analogy, we could say the gauges and the ignition system still carry their 6 volt 'caveman DNA' even though it's a 12 volt car. (because the 'old caveman 6 volt DNA' works better on those two types of electrical circuits)

...so there's two types/two ways they modified the electricity to the gauges; they added an external or an  internal 'voltage regulator' to power up the gauges -both ways are accomplishing the same purpose -so the gauges operate 'the old way' (as they did before when the cars had a 6 volt electrical system... which is better, for this type of electrical circuit because the extra long sending unit wires (as I understand it))

*hopefully, the explanation will help dispel part of the confusion; that's why it-is-the-way-it-is.
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Now if you can measure voltage at the instrument cluster voltage regulator, good!

...but if the gauge is still not working, this basically means two things: 1) bad ground wire/connection to the instrument cluster (follow the copper pathway of the printed circuit; it may lead to a corroded screw connection? -measure the continuity with 'ohms' setting on the muli-meter) ...or #2) the gauge  itself is worn out; the 'electrical spring' inside the gauge is fatigued to a point where it no longer is able to move the needle the way it should

-if you have volts to the gauge and the needle does not move when you ground out the sending unit wire to the tank, this most likely means the gauge is not getting a complete circuit through the ground wire portion of instrument cluster...
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This is an article on an internal voltage regulator type gauge system but the principals are the same and you may glean a clue if only by comparison:

http://www.earlycuda.org/tech/gauge-convert.htm

-shows how to install transistors to accomplish the same purpose

I've done this on four of my AMC cars and it works every time.

Much easier to love the car when the fuel gauge works!
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The AMC TSMs tell the ohms readings for the stock gauges.

It may be a good thing to simply install an add on underdash gauge (choose an aftermarket gauge with the same ohms rating)

good luck (make your own good luck by trying everything/learning everything until you get it working!)

 
Link to XRV8 Race Parts website: http://amcramblermarlin.1colony.com/index.html
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jan/02/2018 at 1:31pm
There is a yellow wire on the fuel gauge. Disconnect that and run another wire from that terminal to ground. Turn the switch on. Gauge should peg. If it doesn't, the gauge is bad. If it does, the wire between sending unit and gauge is bad. You might have to ground the instrument cluster also -- might not get power from the regulator if you don't. I'm assuming you figured out how to read power from the regulator though, since you did note you have checked it and have "about" 5V on the output (which is correct). If the regulator were bad it could be replaced with a solid state 5V regulator instead of the factory bi-metal "on-off 5V average" regulator.

There should be a connector somewhere in or under the trunk in the yellow wire (will be yellow on each side of the connector). That could be corroded, so make sure you clean it. One last thing -- you might want to connect a ground wire from body to sending unit. I just sanded the gas line neck and soldered a wire to it (with the unit off the tank, of course!). The tank is supposed to ground through the body, but rust and corrosion can interfere with grounding.


Edited by farna - Jan/02/2018 at 1:34pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jan/02/2018 at 1:41pm
bigbad is correct on the IVR - 
The behavior of the IVR is more like that of a current regulator... so measuring can be tricky without a volt meter that can handle the cycle of the IVR
And it's not internal vs. external regulation. It's bimetal gauges compared to the moving coil type gauges. 
Once they moved away from the simple bimetal gauges they didn't need that external current regulation. 

You will be amazed at how little voltage drop, how very little a connection needs to be dirty or oxidized to not work properly, so don't just look at things, disconnect and clean from the sender ground and feed all the way to the dash - grounds and all.
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