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Fuel gauge testing


Kool48

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1st. I do have my owners manual,  and have read the testing instructions for fuel gauge.     I have the gauge that came in car plus I bought a 2nd.     My gaugres are 2 wire thermostatic type . Or ginal for my 1948 Plymouth Special Deluxe ,car has been converted to 12 volt before my time.   I'm familiar with the Runtz reducers and I have a few.    I've tested both gauges the same way.   Runtz connected to ( ign sw) lug on both.   I get 12 Volts at input lug and 7 Volts at gauge lug.  1-2 connected from gauge to sender and moving float up and down.  Using a 12 volt battery I ground both gauge and seeing unit (0-30) ohm sending unit ,and yes I've checked it.   It is good . I can not get gauge to do anything at all.   When I test gauge for voltage it seems to be getting the 7 Volts on both sides of the heating bars.     I've researched here and many other places.    Am I testing wrong.  Or are these gauges bad ????    I'm at a loss here.    If there bad , can they be repaired and if so who does it.     I removed resistor from my 2nd gauge since it's being reduced with Runtz.     I've come to the conclusion that my gauges are bad.   But seeking others input before buying another.    Thanks.   Trying to get pics but having problems.     I'm using my Fluke DMM meters.     Thanks in advance 

Edited by Kool48
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I have always been told that sending units don't care about voltage,only polarity. Wouldn't this be the same with gas gauges?

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I converted my 47 Plymouth to 12 volt about 12 years ago. I installed the Runtz voltage reducer on my gas gauge. The gauge quit working after about a week, the Runtz reducer died. I eliminated it from the system.  Gas gauge has been operating off of 12 volts ever since. No problem. 

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Did you ever bench test your fuel gauge ?    I'm curious as to what I may be doing wrong.  I know the sending units seem to be the ones that go bad before the gauge.  My sending , I absolutely know for certain is working.  I've tested it several times now with my ohm meter.     But can't get the gas gauge to do nothing.   

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Had the same problem.. Ended up the unit wasnt getting a ground.  Run a ground wire and it worked then.  Be very carefull if you take the gauge out of the tank.  Unhook battery first.  One spark in the tank opening and caboom !!!!

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Had the same problem. Original gauge did not work tried another did not work, 3rd time I was lucky. I would first try to clean up the gauge using switch cleaner on the points of the gauge and then test it sitting along side the tank and running test wires to the sender before fitting it back in the dash. As my P15 is also converted to 12v I used 2 voltage reducers rated at 10amps each and a fuse box to run fuel gauge, radio and heater fan.

 

Pete

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p15 6v convertor 006.jpg

Edited by Seaside Pete
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All my parts seemed OK, but gauge didn't work. With everything removed for bench test got gauge to move by moving float. Replaced (defective?) wire to sending unit, and new ground from sending unit to body. Problem solved.

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Well I still haven't got either of my fuel gauges to do anything at all  I've had them on the bench for a week or better now.   I have a 3rd coming hopefully this week.    Grounding is not my problem,  cleaned the points also.   I'm getting 7 Volts at the sw Ing stud.   But also have 7 Volts at both 1 and 2 studs on gauge alone nothing else connected.  I am guessing that the working wrapped around the flat heating bars are bad.   I don't know if it should be getting voltage to 1 and 2 studs. The wire I believe has a varnish that should shield it from contacting the bars.   But I could be wrong. I even have a thermo temp gun.  There is no change in temperature when connected to battery or disconnected.  So I know the bar is not heating up and expanding.     Any other thoughts?

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yes...go back and read your book a bit closer on the testing and output of the gauge itself as it is this that provided the voltage to the terminals and that they both go to ground through the same wiper point on the sender and that they spilt the 30 ohms determinate by the position of the wiper in relation to the resistor...you almost there..you just missing a couple key points in theory of operation to complete your trouble shooting and eventual repair..

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On Sunday, October 09, 2016 at 11:26 AM, Plymouthy Adams said:

yes...go back and read your book a bit closer on the testing and output of the gauge itself as it is this that provided the voltage to the terminals and that they both go to ground through the same wiper point on the sender and that they spilt the 30 ohms determinate by the position of the wiper in relation to the resistor...you almost there..you just missing a couple key points in theory of operation to complete your trouble shooting and eventual repair..

Well I still haven't got either of my fuel gauges to do anything at all  I've had them on the bench for a week or better now.   I have a 3rd coming hopefully this week.    Grounding is not my problem,  cleaned the points also.   I'm getting 7 Volts at the sw Ing stud.   But also have 7 Volts at both 1 and 2 studs on gauge alone nothing else connected.  I am guessing that the working wrapped around the flat heating bars are bad.   I don't know if it should be getting voltage to 1 and 2 studs. The wire I believe has a varnish that should shield it from contacting the bars.   But I could be wrong. I even have a thermo temp gun.  There is no change in temperature when connected to battery or disconnected.  So I know the bar is not heating up and expanding.     Any other thoughts?

 

On Sunday, October 09, 2016 at 11:26 AM, Plymouthy Adams said:

yes...go back and read your book a bit closer on the testing and output of the gauge itself as it is this that provided the voltage to the terminals and that they both go to ground through the same wiper point on the sender and that they spilt the 30 ohms determinate by the position of the wiper in relation to the resistor...you almost there..you just missing a couple key points in theory of operation to complete your trouble shooting and eventual repair..

OK now you have me scratching my head lol.    I'll take another good look at my manual.   Not sure what it is that im over looking.   But hopefully it'll hit me.    So may I ask this question.   From what I've said in my past post , does  my gauge (s)  sound like they may be good ?   But my testing procedure is in correct ?   Thanks alot Plymouthy Adams

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Ok.   Well I have read the manual over and over.   Still no positive results.    I don't understand what it is I'm missing here.       When checking for resistance , from the sw ing stud to either 1 or 2 studs on gauge.   I get 30 ohms on #2 stud.  But #1 stud is iffy.   I can get it to read around 26 ohms by moving the heating bar a bit.    But other than that I'm at a loss.    Can someone please tell me what I'm doing wrong based on past couple replies.       Thanks.    I have another ( my 3rd gauge coming.  It'll be here mid next week sometime.     But sure would like to know if my 2 gauges are just bad or not.      Thanks.   

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ok...do you have the sender out of the tank?   of the majority of these sender I have seen that are bad is not due to the resistor...but due to the wipers (float arm) taking the resistor to ground through its single contact common point to both terminal.  The fact that you have 30 ohms across the two terminals speaks well that the resistor is good...now comes the trick....put the float arm in a 1/4 lift position from either  end of the swing...read wiper arm (body of sender) to terminal one..if you get 8 ohms on terminal 1 you should have 22 ohms on terminal two...whatever is on 1 subtract from 30 and see that on terminal two or vice versa...the wiper DOES take both legs to ground at the same time as a common point...this is where many miss the big picture.  If you get no reading to either terminal from the body....I would venture to say that you have lost your ground connecting within the body of the sender..this is a nothing but a pivoting ball socket of the wiper to the body...these rust...these go bad..these can be repaired by disassembly and while cleaning may never get it from being erratic...it will define the problem.  I have found that using braided wicking wire and soldering my own connection to ground very effective...you are free to determine your best course of making/ensuring ground.

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Thanks Plymouth Adams.    I took some pics.   But yes my sending unit is out of the tank and on the bench .   So all testing I have been doing for the past few weeks has been on the bench , sending unit and the fuel gauges.    Using a 12 volt  battery and a runtz reducer on the fuel gauges .             Just noticed that my runtz reducer and another small piece of wiring laying behind sending unit in pics    Those are NOT connected to anything     Just wanted to clear that up. 

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Edited by Kool48
Pics wiring in back ground
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Plymouth Adams ,. Have you got a chance to see my pics here on sending unit testing.    And if so.  Are they ok ?    I'll be getting my 3 rd fuel gauge today through fedex.    So tonight I want to test it on the ( bench ).    With sending unit on the ( bench ) as well.    Any suggestions.     I will be using a 12 volt battery and a runtz 12/6 volt reducer on fuel gauge.     Thanks 

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Well I got my 3rd fuel gauge today.      Hooked up on bench just as I have the others.    No movement from needle at all.   7 volts going in at the SW ING stud.    I made up 2 new wires to go from gauge to sending unit ( it's also on bench ) .  Sender and gauge grounded together at the battery.     I'm at a total loss now.    Can you please tell me what it is I'm doing wrong here.   Or what I need to check for.    This is getting very frustrating.   I've done exactly as the manual says to do.     This 3rd gauge does show me a bit different things when checking resistance ( with my ohm meter) .    It shows around 44 Ohms either way on studs 1&2.      I need help here.  .    Yes I swung the float arm up and down .     Thanks.   

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Ok here is my latest on my testing.   3 gauges.  1st original.  It's shot.   The other 2 I have.  Well I can't get no movement what so ever using a Runtz reducer on the ING SW stud.  And yes it shows 6 volts at stud 12 volts on other end of Runtz.     So I've tried every which way I could and nothing.    Then I just now was messing around with the gauges.    If I connect a straight 12 volts to the IGN SW stud and the ground stud 1 to the  battery then it starts to sweep to full . If I go to stud 2 it goes back to empty.   I don't hold it on more than a few seconds.    But they do move.      So why is it I can't get anything to move when I have 6 volts at the stud.     Keep in mind I'm simply using the power in and grounding  1 or 2.   No sending unit.   Now I have a bit of hope but still am confused.  

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It could be that your voltage reducer is sending out a 'constant current' and not variable. Try the straight 12v or buy a cheap small 6v SLA or a torch battery and then do the testing.

Edited by maok
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7 hours ago, maok said:

It could be that your voltage reducer is sending out a 'constant current' and not variable. Try the straight 12v or buy a cheap small 6v SLA or a torch battery and then do the testing.

What do you mean by a constant current ?       The Runtz has 12 volts in and 6 volts out.   Yes it's a constant current . Should it vary ?    And if so what is the difference of that and a small 6 volt battery  as you mentioned.    I'm confused.   I'll go get the  battery.   Just don't understand what the constant means.   Thanks. 

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The meter works on current (amps, or appropriately- milliamps) not voltage.

ie. when the sender varies its resistance (ohms) this reduces or increases the amps (yes the voltage varies as well) through the meter, which is what makes the needle move in your meter.

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In your meter is a coil of wire, when current runs through the coil it causes a magnetic field which is what moves the needle. The amount of current running through the coil is proportional to magnetic force that pushes the needle.

Edited by maok
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44 minutes ago, maok said:

In your meter is a coil of wire, when current runs through the coil it causes a magnetic field which is what moves the needle. The amount of current running through the coil is proportional to magnetic force that pushes the needle.

 

45 minutes ago, maok said:

In your meter is a coil of wire, when current runs through the coil it causes a magnetic field which is what moves the needle. The amount of current running through the coil is proportional to magnetic force that pushes the needle.

 

45 minutes ago, maok said:

In your meter is a coil of wire, when current runs through the coil it causes a magnetic field which is what moves the needle. The amount of current running through the coil is proportional to magnetic force that pushes the needle.

 

46 minutes ago, maok said:

In your meter is a coil of wire, when current runs through the coil it causes a magnetic field which is what moves the needle. The amount of current running through the coil is proportional to magnetic force that pushes the needle.

 

9 hours ago, maok said:

It could be that your voltage reducer is sending out a 'constant current' and not variable. Try the straight 12v or buy a cheap small 6v SLA or a torch battery and then do the testing.

Well I still haven't got either of my fuel gauges to do anything at all  I've had them on the bench for a week or better now.   I have a 3rd coming hopefully this week.    Grounding is not my problem,  cleaned the points also.   I'm getting 7 Volts at the sw Ing stud.   But also have 7 Volts at both 1 and 2 studs on gauge alone nothing else connected.  I am guessing that the working wrapped around the flat heating bars are bad.   I don't know if it should be getting voltage to 1 and 2 studs. The wire I believe has a varnish that should shield it from contacting the bars.   But I could be wrong. I even have a thermo temp gun.  There is no change in temperature when connected to battery or disconnected.  So I know the bar is not heating up and expanding.     Any other thoughts?

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9 hours ago, maok said:

It could be that your voltage reducer is sending out a 'constant current' and not variable. Try the straight 12v or buy a cheap small 6v SLA or a torch battery and then do the testing.

Won't a straight 12 Volts to gauge burn it up ?     Hence voltage reducer being used.   I'm going to town now to get a 6 volt SLA battery about 12 bucks no biggie.  But when I go to install this gauge back into my car which is now 12 Volts.  I need a voltage reducer correct ?     I think my Runtz went bad last night some how during my testing.   So now I'll have to come up with another reducer of some sort.    

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10 hours ago, maok said:

It could be that your voltage reducer is sending out a 'constant current' and not variable. Try the straight 12v or buy a cheap small 6v SLA or a torch battery and then do the testing.

Will a simple 6 volt lantern battery be sufficient?

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