#81  
Old 03-22-2014, 10:48 AM
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Hit it with some WD-40 and be patient with it (IF it's actually a plug on lead). Try to wiggle it around until you can get it to loosen up. Worst case, you may have to cut the wire at the corroded connector and take the unit out so you can really assess the problem. At that point, you can make a decision on whether to replace the entire sending unit or repair the old one.
The painted trunk floor you mention is also a good idea to check for continuity to the ground wire..
An Ohm meter is very handy in these situations.

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  #82  
Old 03-22-2014, 11:05 AM
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Thanx all.

As i think this through, why do I need to remove that ground wire at all? I'll use the ohm meter or a continuity tester to check for continuity on that wire. But I can also add a jumper ground wire and see if that fixes the problem.

I'll play today. Thanks again.

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  #83  
Old 03-22-2014, 01:43 PM
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Yes, you can use the ohm meter to save you a some time and find out where the loss of continuity is.

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  #84  
Old 03-22-2014, 02:07 PM
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Status update, puzzled:

1. Using ohm meter, measuring the sending unit by touching one wire to lead side terminal, other wire to ground side, I get .36 ohm. The tank should be near full, maybe 18 gallons at least.

2. Taking a jumper wire, connecting lead to ground, the gas gauge is still pinned on FULL with key ON.

3. I get 0 ohm when I measure both ends of ground wire. I cleaned up where the ground wire connects to floor, removing paint. But that didn't spread to be a problem.

Shouldn't test 2 above produce a EMPTY gas gauge reading?

Keep in mind the gauge worked last year. Or so I'm told.

Now what? I fear my testing is poor.

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  #85  
Old 03-22-2014, 03:05 PM
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Yeah, test #2 should have pegged it empty if you were making a good connection...although it's not really a great idea to tie the positive lead to ground with the switch on. You can damage the gauge. Best to use some type of resistor between the wire and the grounding point. 40~50 ohms should give you roughly 1/2 tank reading on the gauge.
I have done it many times without the resistor but I just 'brush' the bare wire to ground, very quickly, so as not to peg the meter. I just want to see it react and move in the right direction.

Really, you have to first verify whether the problem is in the gauge or the sender (or both!). If you had a good connection on that test #2, it may indicate that the gauge is the problem...but... keep in mind that you could possibly have a broken wire anywhere between the gauge pod and the tank on that positive side. Could be why you got no response when you grounded it. That's why I usually check the gauge 'at' the gauge. That is, behind the dash.
On test #1....You may have to pull the sender to really check it while working the arm up and down (I know yours is still in the tank). It should go from near zero to about 90 ohms. (If the '64 has the typical 90ohm rating?)

Really, unless you are making an error somewhere in your testing method, you may have more than one issue. You are getting mixed symptoms. Sending unit reads 'shorted] (.36ohms) but gauge is reading 'open' (full reading)
Choose one thing to address first. I would verify the gauge first. Why is it not responding to shorting the positive lead to ground? Fix that issue first. Make sure there is not a break in the wire somewhere between the gauge and the tank.

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Last edited by Greg Reid; 03-22-2014 at 03:14 PM.
  #86  
Old 03-23-2014, 12:34 AM
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Where does the stock lead wire run? Does it have anything to do with that flat wire under the rear seat? I just want to know where to look to trace it.

next question: what's the easiest way to test at the gauge? How do I access the back of it? (I'm hoping you don't say pull the dash)

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  #87  
Old 03-23-2014, 12:42 PM
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Think of it in this way... The supply voltage is going to be present on the gauge on one side, the circuit passes through the gauge and out the other terminal. From there it follows the wire (under the carpet or wherever) back to the trunk area and down to the plus side of the sending unit. It then passes through the variable resistance in the unit out to the other terminal which goes to ground, ie. the trunk floor.
It's one continuous line from the supply to the trunk floor. Any opening in that line will kill the circuit. It could be the gauge, the sending unit, the wire itself or any connection points between the components. All you have to do is choose the most likely suspects and eliminate them until you find the problem. Start with the easiest to get to.
I've never had to trace the wire. The only reason you would physically have to dig it out is if you can verify that the gauge works but that it's not getting continuity from the dash back to the tank. That would involve verifying that the gauge works when you check it at the dash but does not work when you check it from the tank area.
Sorry...to check the gauge at the dash, you'd have to get to the backside of it.
Check and double check the gauge portion of the circuit from the tank/sending unit.
Here's a kind of diagram...
Batt Voltage--->+(gauge)-<----(wire to trunk)--->+(sending unit in tank)-<--Ground

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  #88  
Old 03-23-2014, 01:26 PM
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Default Older Kent Moore Fuel Gauge Tester

This is a very handy tester to have in cases like this. They show up from time to time on ebay.
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  #89  
Old 03-23-2014, 01:30 PM
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Yeah, that would be ideal for simulating the sending unit resistance.. I used to have a couple of those that we called 'decade boxes' for testing different circuit designs, etc.. Just a bunch of individually selectable resistors. I'm assuming that's the same thing?

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  #90  
Old 03-23-2014, 05:40 PM
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It was too nice out to keep testing, so I just filled up and hit the local cruise! I'll test more later the week.

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  #91  
Old 03-23-2014, 06:35 PM
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Default Fuel sending unit

I' m having a similar problem with an additional twist. My gas gauge has been pegged on full. When I reach just over half a tank, my gauge reads normal, down to empty.
Thoughts?

Thanks in advance for any incite to this problem.
Sully

  #92  
Old 03-23-2014, 07:01 PM
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Quote:
Originally Posted by Sully View Post
I' m having a similar problem with an additional twist. My gas gauge has been pegged on full. When I reach just over half a tank, my gauge reads normal, down to empty.
Thoughts?

Thanks in advance for any incite to this problem.
Sully
A bad spot on sending unit, time for a new one. I would say.

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  #93  
Old 03-23-2014, 07:51 PM
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Quote:
Originally Posted by Sully View Post
I' m having a similar problem with an additional twist. My gas gauge has been pegged on full. When I reach just over half a tank, my gauge reads normal, down to empty.
Thoughts?

Thanks in advance for any incite to this problem.
Sully
Someone explained this scenario earlier in the thread I believe. Bad sending unit.

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  #94  
Old 03-23-2014, 08:25 PM
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Default Flat Wire

The flat wire has a plug on both ends. Back seat to trunk area in the rear and usually left foot kick panel to fuse box area in the front. Grounding the sending unit wire at either plug should send the guage to empty.

  #95  
Old 03-23-2014, 08:36 PM
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I ask because I had the back seat out to install seat belts. I don't think anything was touched, but you never know.

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  #96  
Old 03-23-2014, 09:29 PM
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Default On a 64 model

It wouldn't hurt a thing to check fuses on this car. Guage fuse may only go to the gas guage. Then unplug the sending unit wire (anywhere) and do a voltage check coming from the guage. That is the same wire you ground to force the guage to empty. It is suppose to show voltage but there's no amperage involved, so grounding it is not a problem.
As stated earlier; the sending unit is suppose to ground that wire out (0 ohms/dead ground/no resistance) when the fuel tank is empty.

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  #97  
Old 03-24-2014, 12:05 AM
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I had been thinking along those lines as well QS. I hadn't thought of the fuse specifically but it did occur to me that beyond 'shorting this and opening that'...that a voltage check somewhere along the line wouldn't be a bad idea.

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  #98  
Old 03-24-2014, 09:03 AM
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I'll check the voltage tonight. What is it supposed to be? 12? (with key on and car off)

If the fuse was blown, I would think that the gauge would not go from E to F as I turn the key from OFF to RUN. But I'll look around to be sure.

It's supposed to be very cold and snow tomorrow, which makes it less fun to be in the garage!

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  #99  
Old 03-24-2014, 09:39 PM
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I'm getting .4 volts at the lead wire at the tank. That's with the key ON and engine OFF.

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  #100  
Old 03-25-2014, 12:30 AM
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Just to be sure...you're checking voltage at the positive wire with your voltmeter...and you have a good ground for the negative meter lead?
If so, you have found your issue. You are dropping the voltage somewhere between the source and the sending unit back at the tank.
Get your prints and find out where the voltage is supplied to that circuit and start tracing it until you get to the place where it disappears. Could be a bad fuse, fuse holder, broken or corroded wire or something like that.

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