What the @%@$^ am I doing wrong? - Team Camaro Tech
Electrical & Wiring Troubleshooting electrical.

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post #1 of 29 (permalink) Old Jan 15th, 12, 04:38 PM Thread Starter
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Jimmy
 
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Question What the @%@$^ am I doing wrong?

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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post #2 of 29 (permalink) Old Jan 15th, 12, 04:54 PM
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Re: What the @%@$^ am I doing wrong?

Your meter needs to be on the 200 ohms scale ( speaker symbol ). When you touch your 2 leads together it should read around 1 to 4 ohms or really 0 ohms. Just depends on what kinda shape your leads are in.

Get your meter reading right first and reply back.

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post #3 of 29 (permalink) Old Jan 15th, 12, 05:07 PM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #4 of 29 (permalink) Old Jan 15th, 12, 05:10 PM
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Re: What the @%@$^ am I doing wrong?

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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post #5 of 29 (permalink) Old Jan 15th, 12, 05:17 PM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #6 of 29 (permalink) Old Jan 15th, 12, 05:47 PM
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Re: What the @%@$^ am I doing wrong?

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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post #7 of 29 (permalink) Old Jan 15th, 12, 06:07 PM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #8 of 29 (permalink) Old Jan 16th, 12, 04:10 AM
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Re: What the @%@$^ am I doing wrong?

Yes it sounds like a bad sending unit.

1.9 should be empty.
44.8 should be 1/2 tank.

What does the guage show when the float is all the way down and then all the way up.

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post #9 of 29 (permalink) Old Jan 16th, 12, 10:06 AM
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Re: What the @%@$^ am I doing wrong?

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.

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post #10 of 29 (permalink) Old Jan 16th, 12, 10:50 AM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #11 of 29 (permalink) Old Jan 16th, 12, 10:57 AM
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Re: What the @%@$^ am I doing wrong?

Quote:
Originally Posted by jmys67 View Post
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.

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post #12 of 29 (permalink) Old Jan 16th, 12, 11:06 AM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #13 of 29 (permalink) Old Jan 16th, 12, 11:33 AM
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Re: What the @%@$^ am I doing wrong?

Quote:
Originally Posted by jmys67 View Post
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/approac...runner-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.

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post #14 of 29 (permalink) Old Jan 16th, 12, 10:22 PM Thread Starter
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Re: What the @%@$^ am I doing wrong?

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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post #15 of 29 (permalink) Old Jan 17th, 12, 04:36 AM
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Re: What the @%@$^ am I doing wrong?

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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