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Discussion Starter #1
Im trying to troubleshoot my sending unit. I have a 22gal fuel cell in the trunk. I have an autometer fuel gauge that is a 0-90 ohm? I cant get the gauge to read under 1/4 tank, even when Im holding the sending unit and the float rod is all the way down. The unit does not seem to be hung up in the cell, I can feel when it hits the edge and theres no obstructions.

The sending unit is exactly like http://www.summitracing.com/parts/RCI-7060B/ this one. Heres where I get lost. I have a Sperry DM-5300 multimeter. Im trying to check the ohms correct? Under the Ohms symbol there are the following markings: 20M 2M 200k 20k 2k 200(speaker symbol) and arrow with a + (Hopefully this makes sense)

Ive tried each setting and have yet to come close to 0-90. The reading thats come closest was on the 2k and it went from .01-.45. Now just to confirm Im even doing this right, I have the red lead on the top post of the sending unit and the black to the ground post of the unit? To complicate things, when I try the same setting with the car power on it only displays the .0L on any setting. So....any ideas?
 

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Discussion Starter #3
Mike, i put it on 200 and it says 0L I touch them together and it beeps and shows 00.3...its brand new, the plastic is still on the display window.
 

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I would try another meter for making the measurements or visit Radio Shack or a TV repair shop and get a resistor under 100 ohms for a meter checker.
Tying all the parts together should get a reading lower than 20 ohms.

Arrow with a + sign is a diode and this position is used to check diodes.
When checking diodes, they should have one lead disconnected and use both probes and make a measurement. Reverse the meter leads and measure again. The result of a good diode is a reading under 0.900 and infinity in the other direction.
 

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Discussion Starter #5
Oh ya while were on the subject...confirm that the ground needs to go from the sending unit back to the gauge right? I had it grounding at the trunk and the gauge grounding at the dash.
 

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The way you have it grounded is fine.

Your meter is reading right for ohm readings.

Hook the red lead to the terminal of the sending unit. The black lead on the ground or case of the sending unit.

With the float down is should read 0 ohms and with the float up it should read 90 ohms. The reading might not be exact but close.
 

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Discussion Starter #7
Mike, got a steady beep 1.9 to 44.8...seem like the sending unit? is there anything I can do with the sending unit to check it? Could there be something wrong with the wiring?
 

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I had to work on a similar sender and when hooked up to a dakota digital gauge I would get all kinds of strange readings. We finally took the sender out of the tank and verified we were not always getting a 0-90 (or about that) moving the float arm. The customer then decided, what the heck and we took it apart and bent the wiper arm to where it put more pressure on the windings of wire to read the different ohms and guess what, it started working properly. Evidentally the wiper arm how it was was not putting enough pressure to make good contact all the time through the travel of the float arm.

Just to get familiar with your meter, get some resistors and they should measure close to what they are in value. Resistors have a tolerance of plus or minus 5% or 10% to where if it's a value of 30 ohms it may read 27 ohms up to 33 ohms. Also too some probes the ends become corroded throwing off measurements.

Jim
 

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Discussion Starter #10
Thanks guys...Jim, Ive been tempted to try tweaking the arm, but was afraid it would screw it up if it turned out to be something simple that I was overlooking. Mike, yeah that was the other issue. With the float all the way down it reads 1/4, when I move it up the gauge follows the sweep and shows full at the top of the swing...and thats with it still only reading 44.8 ohms! dont get it.
 

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Thanks guys...Jim, Ive been tempted to try tweaking the arm, but was afraid it would screw it up if it turned out to be something simple that I was overlooking.
Just to clarify, I am talking about the wiper arm and it's contact to the windings of wire inside the sender and not the float arm. Some of the assemblies are fairly easily taken apart while others might be more of a sealed/non-serviceable type.

Jim
 

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Discussion Starter #12
ahh...thanks for clarifying, yeah the black housing seems like it would be easy to pop open. What would I be looking for, or is it a remove and replace?

However, am I wrong in thinking that adjusting the arm would 'technically' solve the problem? Much like you used to be able to adjust the tank water level in the old style toilets by bending the float arm? (sorry for the comparison) or am I oversimplifying this.
 

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ahh...thanks for clarifying, yeah the black housing seems like it would be easy to pop open. What would I be looking for, or is it a remove and replace?

However, am I wrong in thinking that adjusting the arm would 'technically' solve the problem? Much like you used to be able to adjust the tank water level in the old style toilets by bending the float arm? (sorry for the comparison) or am I oversimplifying this.
The sending unit is basically in a little box. Inside this box a wiper arm that attaches to the float arm wipes against a wrapping of wire to get the assembly to read ohm between 0 and 90.

Here's what I came up with with a quick search as to the guts of a sending unit.

http://www.yotatech.com/f116/approach-fuel-sending-unit-88-4runner-199822/

The sending unit has a similar design to a toilet valve but it's not totally the same with how they work. Good thinking though.

The only time you would bend the arm or the mount it is on would be to adjust how the sender reads with what is actually in the tank. If when first installed it and you had 5 gallons left in the tank and you wanted it to actually be 2 gallons, you could bend the arm down and now when the arm was at the full down travel and it sent a 0 ohm signal to the gauge to get it to read empty, you would only have 2 gallons left BUT sometimes doing this affects how it reads on the other end when the tank is full. At full it might not let the float rise to the top of the fuel level but hold it down in the gas and now driving the car takes a long time before the gauge starts to come off of the full mark.

Who knows what is inside yours but put it on a bench and slowly take it apart if you want but be aware there may be a spring or something that might want to pop out. I took apart a relay for a motor the other night and by carefully breaking the assembly apart I could see a spring that wanted to launch out but by doing it slow I knew it was there and could grab it before it flew out and if it would have I know it never would be found again.

Jim
 

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Jim, ok I prob shoulda done this earlier but I took it off to see if there was an issue with the internal arm. I tested it without being hooked up and it read .002 to .093. So its not the sending unit after all. I hooked it back up and I'm now getting a reading of .019 to .051 and the gauge isnt moving past 1/4 when it used to show full when I held the arm to the top...

oh another odd thing when I was testing it out of the car, I would get the reading and the steady beep from the meter until about 3/4 of the way up then the beep would stop but the numbers still reached 93...any reason?
 

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The meter is set internally to beep at a predetermined low resistance. Once passed the point, the beeping stops. Can't change this function unless you buy a better upscale DMM.

One feature you are looking for in checking out the sending unit, while measuring the resistance through the arc, there should be no breaks/opens during the sweep of the float.

The next step I would perform is set up the s/unit, as if installed in the tank, ground the chassis in the normal spot, disable the ign or jumper battery voltage to the gauge circuit, just as the ign/acc circuit does normally, and slowly swing the float through its arc a few times making sure the gauge indicates the pseudo fuel level. This way you will have confidence the gauge circuit works. Any problems later and you can rule out this circuit in your troubleshooting the problem.
 

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Jimmy,

Now that you got the float out and it actually reads 0 and 90 when the float is up and down means the float is good.

Is this a factory guage in the dash? You should be able to ground the wire in the trunk that goes to the guage. Turn the key on, it should show empty. When you unground the wire in the trunk with key on it should show past full.

If it does this then the wiring and guage are good. If it doesnt then its the guage or wiring to the guage.
 

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Discussion Starter #17
Ok, so at least I have the float off the list! Mike, the gauge is a 2/16 autometer electrical fuel gauge. Now, to complicate things, (for this part of it) there is no 'key'. There is a hidden cut off switch that runs the power. So thats basically my key you just want me to have power to the gauge correct?

now, I did have the gauge grounded to the trunk and the gauge grounded to behind the dash. I ran a ground wire from the gauge straight to the gauge to see if that could be the issue. The instructions say 'connect wire from gauge center terminal [GND(-)] to ground on fuel tank (but not specifically the sending unit). So I can go back to the way I had it (gauge to dash, sending unit to trunk?)

I tried taking the gnd off with power and it goes to bout the 1/4 mark. But I think I found a prob. I took the IGN wire off the gauge and with the switch on I still had 12v at the S (sender) terminal at the gauge. There shoudnt be any power showing from the sender terminal...right?

I prob damaged the meter since in the instructions theres a bold caution: be careful not to touch the ign wire to the S terminal (and its been like this for awhile). Prob means there shouldnt be power to it too...

Everett - so I remove the gauge, move to the truck, hook up the S from the sending unit to the gauge, ground the gauge and sending unit and run power from the batt to ign of the gauge? Basically the same way it was in the car?

PS thanks the patience...
 

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so I remove the gauge, move to the truck, hook up the S from the sending unit to the gauge, ground the gauge and sending unit and run power from the batt to ign of the gauge? Basically the same way it was in the car?...
Yes, just as it was installed in the car. Jumper battery/test voltage to the gauge power terminal, not S terminal, ground, and the manf suggests grounding the gauge to the s/unit ground connection on the body so both items have the same ground point, not a bad idea, body rust and welds do have a way with a return path, and tan wire from s/unit to S terminal.

If gauge is in good working order, it should indicate fuel level in accordance with float movement.

Then install set-up in the car as for real and test. Whether or not the gauge will work with the above set-ups, time will tell.

Correct, there should not have been battery voltage on S terminal. This would be a test to see how much smoke the manf packed into the sending unit.

You might take the DMM on OHMS setting and measure across the gauge by itself to see if the needle ever moves across the scale. Some meters will move, others won't. Try it both ways with the meter leads. If it does move across the scale, then meter, I would think, would be good. The test set-up in the first paragraph will determine the circuit validity.
 

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You can certainly put the gauge in the trunk and wire it up for testing.

The fuel gauge could care less whether it has a constant 12 volts to it or 12 volts when the key is in the run position. Since the gauge will draw power and you probably only need to read the fuel level while driving you would want it on a keyed 12 volt circuit.

To bench check a fuel level gauge you will need a source of 12 volts and ground (and not from a battery charger but either a stable 12 volt power supply or a fully charged 12 volt car battery).
You then need to identify which terminal on the backside of the gauge needs 12 volts and then with a jumper wire solidly connect this terminal to the power supply or batterys positive 12 volt terminal. Ideally, also put inline a small amperage fuse so that if there is a problem the fuse will blow.
You then need to identify which terminal on the backside of the gauge needs to be grounded and then with a jumper wire solidly connect this terminal to the power supply or batterys ground terminal. It's likely that some gauges may not have a dedicated ground terminal but instead require the gauges body itself to be grounded.
With just these two connections to the fuel gauge the gauges needle should go to the full or above mark. If either of these connections are broken then the gauges needle may stay at the above full mark or may drop to some other point but it is not of any concern.
Now with the gauge having 12 volts and ground to it and no connection to the "S" terminal (sender terminal) the gauges needle should then go to the full or above mark.
If we then take a jumper wire and solidly connect the "S" terminal to ground then the gauges needle should then go to the Empty or below mark.
With these tests if we can deflect the gauges needle to full or above and then to Empty or below chances are real good that the gauge is good. Further tests with resistors could then be done to see how well the accuracy is on the gauge itself.

Now if we then want to wire in a fuel tanks sending unit to the gauge we then have to solidly connect the sending units "S" terminal or it's output terminal to the gauges "S" terminal and then connect the body of the sending unit or it's labeled ground to the same ground point that the gauge is connected to.

Now with all of this connected the gauges needle may be anywhere between empty and full. If we were then to hold the sending unit like it would be in the gas tank, the float arm would hang down and the gauge should read empty or below. If we slowly raised up the float arm the gauges needle should also slowly go higher and then at a point the float arm is up all the way, then the gauges needle would point to full or above. If while slowly raising the arm the gauges needle jumps to an unrelated value then there may be a dead spot inside the sending unit assembly. When this dead spot occurs the float arm may only be halfway up but then the gauges needle goes to above full and then with a little more upward travel of the float arm it then has the gauges needle reading right then this would indicate a dead spot (open connection or a connection above 90 ohms).

I hope this helps and doesn't cloud things up.

Jim
 
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