jamesromeos
Well-Known Member
any recommendation on how to determine weather a sender for the temperature gauge is working or not? I'm getting no reading on the dash gauge which is factory also how do you figure out if a fuel gauge is bad?
1968 barracuda temp gauge and fuel level inop
- Thread starter jamesromeos
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I had the same problem with my 66 Barracuda. I searched around the electrical forums and found some great information. And, several very smart FABO members helped me get mine going!! I'm not sure of the difference between years but the 66 has a voltage regulator inside the gas gauge that drops the 12 volts from the battery down to 5 volts to operate the gas and temp gauges. In these old cars the regulator goes bad.
I replaced mine with a 7805 regulator from Radio Shack and now have a working gas gauge. There are several great threads that have great info. Here's one link.
http://www.forabodiesonly.com/mopar/showthread.php?t=292861&highlight=sending+unit
I replaced mine with a 7805 regulator from Radio Shack and now have a working gas gauge. There are several great threads that have great info. Here's one link.
http://www.forabodiesonly.com/mopar/showthread.php?t=292861&highlight=sending+unit
Oil gauge operates on same regulator as temp and fuel. If oil gauge works regulator is not the problem. Must be 837642 threads here about these gauges. Read them all. Pay attention to the percentage of do it yourselfers who do it over and over again.
Even if a solid state regulator does get needle movement from these 40 to 50 year old gauges, they aint gonna be accurate.
Even if a solid state regulator does get needle movement from these 40 to 50 year old gauges, they aint gonna be accurate.
Pete in NH
Well-Known Member
Hi,
For a quick test disconnect the temperature sending unit wire and with the ignition switch in the run position you should see a pulsing voltage on a meter or test light between that wire and ground. If not the instrument regulator is likely bad. Also, a 27 ohm resistor from Radio Shack between that wire and ground should give a half scale reading on your temperature gauge. It's the same for the fuel gauge, that 27 ohm resistor should give a half scale reading.
Let us know what you find.
For a quick test disconnect the temperature sending unit wire and with the ignition switch in the run position you should see a pulsing voltage on a meter or test light between that wire and ground. If not the instrument regulator is likely bad. Also, a 27 ohm resistor from Radio Shack between that wire and ground should give a half scale reading on your temperature gauge. It's the same for the fuel gauge, that 27 ohm resistor should give a half scale reading.
Let us know what you find.
68gtxman
I used to reMember
Disconnect the wire on the fuel sending unit and ground it. Turn on the ignition switch to "run" and see if the gauge moves. If so, the gauge is good. Look for a missing ground strap at the sender to the steel fuel line. You can add a ground there and if that fixes it you're good to go. If not, then replace the fuel sender.
jamesromeos
Well-Known Member
Temp gauge test with a multimeter fluctuated when hooked up to the ground .01-.03 would that tell me that the gauge is fine?
jamesromeos
Well-Known Member
I need to go to radio shack tomorrow to test it further.
OK if you're going the do it yourself route for testing... 23 ohms is the center of the gauge, not 27.
A solid state regulator will not live very long in a corrupt circuit. There are manners in which the original mechanical limiter failure is corrupt so bend the little thingy doesn't fix anything. And in most cases, a solid state regulator will provide needle movement only. Gauge accuracy is gone. Good luck though.
Pete in NH
Well-Known Member
I mentioned a 27 ohm resistor as that is a value Radio Shack might have in stock It will be close enough to give a reading on the gauge close to the center. Stock resistor values run 22 and 27 ohms with 10% tolerance resistors and there is a 24 ohm 5% value as well. Radio Shack is unlikely to stock any thing other than 10% values.
The readings you measured with your meter on the temperature sensor line are very low and I suspect so low that there really isn't anything there.
The readings you measured with your meter on the temperature sensor line are very low and I suspect so low that there really isn't anything there.
jamesromeos
Well-Known Member
so would it be right to guess the gauge is bad, or the resistor? Next question, if the gauge is bad, are they able to be removed from the bezel to be replaced?
After the instrument panel is removed from the dash and placed face down on the workbench. The plastic bezel is removed, then gauges can be removed.
The rally inst' panel you have is one of the more difficult to remove. Standard panels don't encompass the radio and climate controller so those are easy by comparison. Even so, lots of owners have struggled to remove standard panels.
You're going to need a factory service manual.
Pete in NH
Well-Known Member
I would not start guessing about what is bad or not. You can make a lot of work for yourself by guessing. If your meter has an ohms position you can measure the temperature sensor in the engine block. From the center terminal on the sensor to ground it should read around 70 ohms cold to around 20 ohms at operating temperature.
Also, this has been asked before but does your oil pressure gauge work correctly?
There are quite a few things that can be the problem even though these gauge systems are fairly simple. You would not want to pull the whole dash apart only to find out there was an open wire somewhere in the engine compartment. I would do some simple trouble shooting before making any guesses.
Also, this has been asked before but does your oil pressure gauge work correctly?
There are quite a few things that can be the problem even though these gauge systems are fairly simple. You would not want to pull the whole dash apart only to find out there was an open wire somewhere in the engine compartment. I would do some simple trouble shooting before making any guesses.
cudajim
cudajim
You may also want to check your ignition switch, they tend to go bad or at least open up causing the fuel gauge regulator not to get 12 volts while the engine is running. You can possibly fix it easily by taking it apart and soaking it in WD-40 so the contacts make connection to ign1 and ign2.
As mentioned above, the problem could also be the in dash regulator (likely), the sending unit in the gas tank, the ground strap at the sending unit, the wiring from the tank up to the gauge or lastly and most unlikely the gauge itself.
As mentioned above, the problem could also be the in dash regulator (likely), the sending unit in the gas tank, the ground strap at the sending unit, the wiring from the tank up to the gauge or lastly and most unlikely the gauge itself.
jamesromeos
Well-Known Member
Oil pressure works fine
nm9stheham
Well-Known Member
Is that an oil pressure gauge, or an oil pressure light? An oil pressure light circuit has nothing to do with the circuit that feeds the temp and fuel gauges, so the operation of an oil pressure light is not of any use in troubleshooting this problem. An oil pressure gauge IS fed by the same circuit at the other 2, but most of these cars have oil pressure lights only.
BTW, you asked about testing the temp gauge sender; you can test that to see if it is good. Put your multimeter on the resistance (ohms) mode, and select the lowest scale (usually 200 or 400 ohms). Heat the sender up in the engine or in a pot of water with a thermometer to around 180 F. After the engine is warmed up normally, disconnect the wire from the temp sender and check the resistance from the sender's connection to the body of the temp sender; it should read in the range of 20-35 ohms; the exact number will vary depending on the exact temperature and the actual sender, but it should be around that range with a 180F thermostat and normal temps. I do this when driving; I just stop after the engine is warmed up, disconnect the wire and make a resistance reading on the spot.
When you tested the temp sender before and got .01 to .03, was that volts or ohms? An ohms reading while the wire is connected is meaningless. If that was volts, then something is wrong in the dash with the gauge or the voltage limiter in the dash. Read the voltage out of the wire to the temp sender with the wire removed from the sender, and the key in RUN; you should see the voltage jump up and down erratically from as low as near 0 volts to up near 8 or 10 volts typically; each meter reacts differently to this.
The voltage at this wire should be a pulsed 12v if the voltage limiter in the dash is good and the gauge is good; meters don't read this pulsed voltage well. It is actually easy to see by connecting a 6v, 1 watt lantern battery from the wire to ground; it will flash brightly about once per second. You can get such a bulb at Radio Shack: model 40 or model 1847. (Pick up some test leads with alligator clips while you are there....) You can run the same test at the wire to the fuel guage. If the bulb flashes brightly, then if you leave the bulb connected for 10-15 seconds in either circuit, then the associated guage will read on-scale if it is good.
Pete mentions the 27 ohm resistor (or 24 or 22); you can use that as a sensor substitute in either the fuel gauge circuit or the temp gauge circuit; either gauge will read around half way with a resistance in the mid-20 ohms range put in place of the sensor.
BTW, you asked about testing the temp gauge sender; you can test that to see if it is good. Put your multimeter on the resistance (ohms) mode, and select the lowest scale (usually 200 or 400 ohms). Heat the sender up in the engine or in a pot of water with a thermometer to around 180 F. After the engine is warmed up normally, disconnect the wire from the temp sender and check the resistance from the sender's connection to the body of the temp sender; it should read in the range of 20-35 ohms; the exact number will vary depending on the exact temperature and the actual sender, but it should be around that range with a 180F thermostat and normal temps. I do this when driving; I just stop after the engine is warmed up, disconnect the wire and make a resistance reading on the spot.
When you tested the temp sender before and got .01 to .03, was that volts or ohms? An ohms reading while the wire is connected is meaningless. If that was volts, then something is wrong in the dash with the gauge or the voltage limiter in the dash. Read the voltage out of the wire to the temp sender with the wire removed from the sender, and the key in RUN; you should see the voltage jump up and down erratically from as low as near 0 volts to up near 8 or 10 volts typically; each meter reacts differently to this.
The voltage at this wire should be a pulsed 12v if the voltage limiter in the dash is good and the gauge is good; meters don't read this pulsed voltage well. It is actually easy to see by connecting a 6v, 1 watt lantern battery from the wire to ground; it will flash brightly about once per second. You can get such a bulb at Radio Shack: model 40 or model 1847. (Pick up some test leads with alligator clips while you are there....) You can run the same test at the wire to the fuel guage. If the bulb flashes brightly, then if you leave the bulb connected for 10-15 seconds in either circuit, then the associated guage will read on-scale if it is good.
Pete mentions the 27 ohm resistor (or 24 or 22); you can use that as a sensor substitute in either the fuel gauge circuit or the temp gauge circuit; either gauge will read around half way with a resistance in the mid-20 ohms range put in place of the sensor.
Pete in NH
Well-Known Member
A 68 Barracuda has a real oil pressure gauge. If the oil pressure gauge is working and reading correctly the instrument voltage regulator is likely okay. That would leave sending unit, wiring or gauge issues for the non working fuel and temperature gauges.
nm9stheham
Well-Known Member
^^ Ah yes, Pete, I missed that this was a Barracuda..... and you are right on the oil pressure gauge working off of the voltage limiter as well as the fuel and temp gauges.
jamesromeos
Well-Known Member
Oil pressure gauge is fine. working great, as is the ampmeter
The OHMs on the multimeter set to 200 again, in the ohms setting is only gong to like 1.2 ohms with the multimeter black grounded, and the red going to the sender post with the wire unplugged and the key in the on position.
I am prob. doing it wrong, and if someone can explain how to test this for a "dummy" it would be helpful. I feel like im doing something wrong.
also the fuel gauge is still inop...I tried to ground it out to the frame to no avail. I see the ground strap on the fuel line, It looks fine, a little coroded so I cleaned it as best I could, still nothing.
What a pain in the A$$
The OHMs on the multimeter set to 200 again, in the ohms setting is only gong to like 1.2 ohms with the multimeter black grounded, and the red going to the sender post with the wire unplugged and the key in the on position.
I am prob. doing it wrong, and if someone can explain how to test this for a "dummy" it would be helpful. I feel like im doing something wrong.
also the fuel gauge is still inop...I tried to ground it out to the frame to no avail. I see the ground strap on the fuel line, It looks fine, a little coroded so I cleaned it as best I could, still nothing.
What a pain in the A$$
BillGrissom
Well-Known Member
Pete in NH
Well-Known Member
Set your meter to the 200 ohm range. Touch the two test probe leads together, the meter should read zero or close to it. Put the black lead from the meter on the temperature sender base where it screws into the engine block. Scrape it around a little to clean off the metal a bit. Put the red meter lead on the center post of the temperature sender and again scrape it around a bit. Okay, now read the meter- it should be somewhere between 10 and 80 depending on engine temperature. 80=cold, 10= really hot. Normal engine temperature should be somewhere around 25 or so ohms. If you get the same reading you got with the meter leads held together the sensor is shorted and will need to be replaced and it may have taken out the gauge. If the sensor reads above 80 ohms it is bad and will need to be replaced.
While 80 or more ohms = no needle movement in the gauge, a temp sender can go a long way beyond that and still be good. Oil and temp senders don't have fixed limits like fuel senders.
Buy one anyway. They don't cost much.
Buy one anyway. They don't cost much.
jamesromeos
Well-Known Member
Is this the right setting for testing resistance
Pete in NH
Well-Known Member
Yes, you're all set to measure the temperature sending unit. Let us know what reading you get.
nm9stheham
Well-Known Member
Right, the temp gauge sender readings can go to many thousands of ohms when fully cold; some of the newer ones seem to reach a 'break point' when cooling down where the resistance goes essentially 'open' (very, very high resistance).
OP, after you have tested the temp sender resistance, put your meter back on the 20V scale, connect the black lead to the temp sender case or alternator case (a good ground on the engine), and connect the red lead to the wire for the temp sender while it is disconnected from the temp sender. Turn the key to RUN and see if the voltage is jumping up and down between very low and as much as 12V.
If the sender resistance is as low as the 1.2 ohms that you measured, it may have burned out the Voltage Limiter or the gauge as Pete mentioned. Since the fuel guage does nothing with the fuel sender wire groudned, I would susepct the Limiter first. So both tests are needed.
jamesromeos
Well-Known Member
I suspect the limiter may be the issue. I was getting low readings 1.3, 1.4 and with the wire grounded the gauge did not move. any way of testing the limiter? where is it located? the ampmeter and oil gauges are working fine.
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