Fuel Gauge and Temp Gauge not working

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Fuel Gauge and Temp Gauge not working

Postby pgillott » Thu Nov 17, 2016 7:32 am

New to this site but this group is AMAZING! Need some help. Im also having a fuel gauge and temp gauge issue that i can't resolve. Heres where i am. (71 dodge sweptline 318 motor) Gas gauge and fuel gauge are both needle all the way to the left once car is hot and full of gas. 12v confirmed on left brass spade terminal on gas gauge. Top center post has pulsing voltage. Its a challenge to read on my digital volt meter but it seems to pulse from 0-3.96. It could be getting up higher but the meter doesnt have time to get there because it changes so fast. Should that be higher? The gas gauge isn't moving, as previously mentioned, but if i ground the sending unit wire on the gas gauge to the chassis, after 5 or so seconds, the gas gauge begins to pulse up in small swoops. till it gets to the full mark. So I think the gauge is good. My sending unit could be bad but i haven't gotten into the tank yet. Its aftermarket and under the bed. My main concern is the temp gauge. It functions the same as the gas gauge. If I take the sending unit wire from the gauge and ground it, after 8 seconds, it will begin to make small swoop until it gets to the right of the gauge. I also found the temp sending wire next to the thermostat on the engine where it attaches to the temp sensor. I removed the wire from the sensor and attached it to the block and the gauge does the same as grounding it inside the cab. After a few seconds it begins to move in small sweeps. After this test i assumed that the temp sensor was bad so i replaced what looked to be a new sensor. Still no movement on the temp gauge once the engine is clearly warm. Im stumped...any advice would be appreciated. Could the voltage regulator in the gas gauge be dying and creating too much resistance and not allowing the voltage to get high enough or is there something else going on. THANKS IN ADVANCE!!!
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Re: Fuel Gauge and Temp Gauge not working

Postby MadMC63 » Thu Nov 17, 2016 10:13 am

Based on what you've written the fuel gauge is the problem. The fuel gauge receives 12V in and the voltage is reduced by a thermal resistor to approximately 5V's. I believe the OEM resistor pulses between 7 and 5V's. If you're seeing a pulse through the gauge function on both the fuel and temp gauge the internal limiter is going. If you have verified that the 12V in does not pulse that's the only real conclusion. Here's a schematic for a digital voltage limiter. It's easy enough to build and works flawlessly.
Voltage limiter.jpg
Voltage limiter.jpg (15.44 KiB) Viewed 699 times
1971 Dodge D100
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Re: Fuel Gauge and Temp Gauge not working

Postby Hobcobble » Thu Nov 17, 2016 11:28 am

:goodpost
Welcome to the site. :welcome :usa I ended up making voltage
limiters for three of my Sweptlines. No more worries. :Thumbsup
John
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Re: Fuel Gauge and Temp Gauge not working

Postby pgillott » Thu Nov 17, 2016 1:50 pm

You guys are awesome! So does the resistor go inline where the 12v comes in to the gas gauge? Basically it steps it down then would attach to the 12v terminal on the gas gauge? Or do i have to open the gauge up and attach inside of it. Ive attached a pic of what I'm looking at. FYI...The send wire to the temp gauge and the sender wire to the tank are unhooked.
Thanks
Pete
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IMG_6829.JPG
IMG_6829.JPG
gas gauge is on the far right.
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Re: Fuel Gauge and Temp Gauge not working

Postby MadMC63 » Thu Nov 17, 2016 2:22 pm

That's right Pete. Run 12V to the digital voltage limiter and then from the limiter to the 12V connection on the back of the fuel gauge. Don't forget to use some type of heat sink.
Good luck, Joel
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Re: Fuel Gauge and Temp Gauge not working

Postby pgillott » Thu Nov 17, 2016 10:05 pm

My confusion is that there seems to be a buss bar that runs from the 12v terminal on the back of the gas gauge to the the amp gauge thats next to it. Im assuming that the red wire in the pic above feeds 12 volts to the gas gauge and the amp gauge through that brass buss bar. Isn't stepping down the voltage on the 12v spade wire that connect to that terminal/buss bar down to 6v, going to mess up the amp gauge. Do I need to disconnect the bus bar from the back of the amp gauge and supply a full 12v to it or is my assessment of the schematic wrong?
Thanks again
pete
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Re: Fuel Gauge and Temp Gauge not working

Postby MadMC63 » Fri Nov 18, 2016 8:03 am

Yes, the 10 gauge red wire supplies 12V to the fuel gauge. No, the buss bar does not power the amp gauge. The amp gauge has it's own, separate wiring hidden by the buss bar in the picture. Here's the tech link I got the schematic from.
viewtopic.php?f=33&t=22961
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Re: Fuel Gauge and Temp Gauge not working

Postby Txas2step » Fri Nov 18, 2016 1:43 pm

You need to step down the 12v to the fuel gauge to 5v with a limiter. You can make one or they are available on Ebay. Jumps to temp gauge from fuel. 12 volts will fry both.Been there on 2 swepts. :pale .
61 shorty 170/ 3spd 3:91(sold)
66 lwb 318 poly/727/4:10 (sold)
67 shorty 318poly/4spd 3:55
68 ute 318/3 spd/3:55(sold)
70 318/727/3:23
66 d200 225/4spd/4:10( military)(sold)
68 d100 383/727/3:55
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Re: Fuel Gauge and Temp Gauge not working

Postby Hobcobble » Fri Nov 18, 2016 3:43 pm

Txas2step wrote:You need to step down the 12v to the fuel gauge to 5v with a limiter. You can make one or they are available on Ebay. Jumps to temp gauge from fuel. 12 volts will fry both.Been there on 2 swepts. :pale .


I think I stepped from 12v to 8v... then to 5v as per the first diagram in this
thread. :study I used a thick chunk of aluminum as a heat sink and put it
together with a couple of rivets. :idea :2cents
John
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Re: Fuel Gauge and Temp Gauge not working

Postby pwadventurer » Fri Nov 18, 2016 7:58 pm

pgillot, I haven't done this conversion yet, but what I read about it is, you need to move the red 12 volt feed wire on the fuel gauge to one of the bus bar stabs. Remove nut and bend bus bar tab on back of 12 volt fuel gauge stud up away of stud, replace nut. This isolates fuel gauge from 12 volts. Run 12 volts to new regulator from bus bar. the 5 volts from new regulator goes to the same 5 volt terminal on fuel gauge that also feeds temp gauge. Hope this helps.
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Re: Fuel Gauge and Temp Gauge not working

Postby wally426ci » Sat Nov 19, 2016 5:48 pm

I use the ivr3 voltage limiter for mine with no issue :salut
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Re: Fuel Gauge and Temp Gauge not working

Postby Txas2step » Sun Nov 20, 2016 7:20 am

wally426ci wrote:I use the ivr3 voltage limiter for mine with no issue :salut


I made a step down from 12 to 8 to 5 on my first one. 2nd one, a used what Shawn has here ivr3. :Thumbsup
61 shorty 170/ 3spd 3:91(sold)
66 lwb 318 poly/727/4:10 (sold)
67 shorty 318poly/4spd 3:55
68 ute 318/3 spd/3:55(sold)
70 318/727/3:23
66 d200 225/4spd/4:10( military)(sold)
68 d100 383/727/3:55
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Re: Fuel Gauge and Temp Gauge not working

Postby 6969 » Sun Nov 20, 2016 8:55 am

I have just upgraded the 5v limiter to electronic.

I disconnected the 12V feed to the fuel gauge completely. That's going to the electronic now, no connection on the fuel gauge. The connector to the temp gauge now has the output of the electronic limiter connected as well.

The electronic limiter is a 7805 (1.5A version). I soldered two tiny 10n condensers between input + gnd and output + gnd, directly at the 7805's pins. Further, I shortened the input-pin of the 7805 and soldered a 1N4004 rectifier to cope with wrong input. One further rectifier (1n4004) was put out-to-in between output and input of the 7805, also directly at the pins. Input was then connected to the open 12V wire of the fuel gauge. To connect gnd, I mounted a heat sink to the 7805 and bent it, so I could mount it under the screw of the condenser which is mounted on the back side of the instrument cluster.

Always check your limiter on the bench first.

Be aware, even though your individual application of any voltage limiter might seem to work just fine, but it is a car-application, with all kinds of weired things going on on the wires. Better to have appropriate protection against any faults. :thinking
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Re: Fuel Gauge and Temp Gauge not working

Postby pgillott » Mon Nov 21, 2016 7:42 pm

So i received the aforementioned parts and got to work today. Benched tested the voltage limiter and got a constant 4.98volts. Took it to my truck, pulled the 12v female spade from the gas gauge, hooked it to the male spade on my limiter, grounded my limiter and attached the male spade terminal to the terminal on the back of the gas gauge where the 12volts was hooked up. Nothing on either gauge. To side step the gas gauge, I attached my voltage limiter to the back of the temp gauge with the engine hot and running and still nothing. I verified the voltage on my limiter again and it is still sending a good 4.98v. Took the wire off of the temp sending unit in the block and grounded it. The temp gauge slowly moved to the half way point and stopped. My assessment is that the gauge is bad. Am I correct? Remember i side stepped the gas gauge because I have an aftermarket tank and there is not sending unit in the tank but that shouldn't mater. I need the temp gauge.
Thanks again for any advice.
pg
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Re: Fuel Gauge and Temp Gauge not working

Postby MadMC63 » Mon Nov 21, 2016 8:43 pm

If you supply 5V to the fuel gauge and run the fuel sender side straight to ground the gauge should read full, peg. The same applies to water and oil. If they don't the gauge is bad. All the gauges ground thru the sending units. Once you've tested your gauges then verify their sending unit wire. At that point you're left with the actual sending unit.When testing, the assumption is that the gauge is properly supplied by a working voltage limiter at 5V.
Fuel gauge at empty, half and full.
L= 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H= 10.2 Ohms (full)
Unfortunately like the A,B and E bodies once the limiter goes so do the gauges in a lot of cases.
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Re: Fuel Gauge and Temp Gauge not working

Postby pgillott » Mon Nov 21, 2016 9:08 pm

So where do i get a temp gauge? Any recommendations?
pg
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Re: Fuel Gauge and Temp Gauge not working

Postby powerwagon54 » Mon Nov 21, 2016 9:20 pm

pm sent
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Re: Fuel Gauge and Temp Gauge not working

Postby 6969 » Tue Nov 22, 2016 12:55 pm

The output of your newly made voltage limiter needs to be hooked up on the other side of the fuel gauge - not the 12v in (formerly connected), but the side which is also connected to the temp gauge.

With 5V fed to the 12V-input, your gauges will not show anything.
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Re: Fuel Gauge and Temp Gauge not working

Postby pgillott » Tue Nov 22, 2016 7:56 pm

That is the opposite of what two other have said. Im inclined to agree with you and thats why I asked that question earlier in the thread but i was told it goes back on the same terminal.
PLEASE ADVISE
pete
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Re: Fuel Gauge and Temp Gauge not working

Postby MadMC63 » Tue Nov 22, 2016 9:43 pm

All technical issues aside It's obviously been done both ways with success you pick.
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