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Old Jun 18, 2020 | 07:45 PM
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Dash Issues

My fuel gauge will not read correct. I have replaced the sending unit already and that did not fix it. Grounded out wires to check if gauge works and it checks out correct.

I tested the ohm range of the sender and it checked to be the correct range. I have added a new ground at the sender. (Where are the grounds behind the dash I cannot find it)

I wouldn’t think that it’s the ICVR but it may be a bad connection on one prong (temp gauge reads around 170 once warmed up is this correct?)

tommorrow I am going to replace the wires however I do not think that will resolve the issue because it sometimes reads correct, but then will return to empty.


any pointers? I’ll try anything
 
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Old Jun 18, 2020 | 08:07 PM
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What's the gauge doing? Reading high, reading low, doing nothing, or doing the Hula? If the sender float is fuel logged (pinholes) it will sink, though flop around on the road and cause wild gauge swings.

The ICVR will affect both the fuel and temp gauges, if defective. The temp gauge was apparently never known for being particularly accurate. I think there is actually some calibration or adjustment range on the temp gauge itself, if one is very careful. Maybe swear off coffee for a day or two, it is a fragile mechanism.

The fuel sender float arm height can be adjusted via set-screw on the aftermarket units to calibrate the gauge indication.
 
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Old Jun 18, 2020 | 09:26 PM
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So when I plugged the sender in it would read correct, then after driving it goes down to empty. Occasionally it will pop back up to the correct reading but shortly, as in 30 seconds, it goes back to reading empty.


I also did test the float in a bowl of gasoline for an hour and it never had any inside it.

I would think it’s a bad ground but I don’t know where the grounds are, or it may be one prong in the ICVR that has rusted out, it is the original unit - just some recent thoughts
 
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Old Jun 19, 2020 | 09:01 AM
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I replaced my trucks’ sending unit when I first got it, with an aftermarket ( Chinese ) one from a formerly reputable supplier(DC). It failed. Bought an NOS Ford one, at quite a premium in cost, and all is well now. I even bought another for my parts stash, so should be good for the rest of my life.
 
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Old Jun 19, 2020 | 11:35 AM
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Used A replacement twice and I know it’s not the unit itself because it will read the correct resistances and occasionally read correct. If I bang on the tank for a minute straight it will go back but once driving it will go back down.

I know it’s got to be a bad connection somewhere but I have no clue where
 
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Old Jun 20, 2020 | 09:23 AM
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Tweak the key in ignition a little. It could just be the position of the key it rebounds to once started.
 
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Old Jun 20, 2020 | 12:10 PM
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What do you mean? Turn it more to make a good connection?
 
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Old Jun 20, 2020 | 12:39 PM
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Originally Posted by 1966F100SC
So when I plugged the sender in it would read correct, then after driving it goes down to empty. Occasionally it will pop back up to the correct reading but shortly, as in 30 seconds, it goes back to reading empty.


I also did test the float in a bowl of gasoline for an hour and it never had any inside it.

I would think it’s a bad ground but I don’t know where the grounds are, or it may be one prong in the ICVR that has rusted out, it is the original unit - just some recent thoughts
The way we used to test the floats in aircraft carbs was to get a pot of water, bring it to just under boiling and submerge the float in it. It will start blowing bubbles if there is a hole in it and if it has gas in there you hold the hole to the bottom side and when it heats up it will force the gas out. Then solder up the hole and retest. If it has a hole in it, it will start blowing bubbles almost as soon as it is put in the water. Word of caution if it has fuel in it don't do this on your wife's gas stove in the kitchen.
 
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Old Jun 20, 2020 | 08:52 PM
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Tested float in boiling water and it checked out fine.

I also replaced the orange cable to sender with a new one and made a new ground directly to cab floor.

I also made a dedicated ground from dash to firewall. I’ve yet to replace the ground from engine to firewall but that’s the goal for tomorrow.



I noticed tonight that after changing the wires the needle stayed correct for the majority of the two mile trip, but on the second mile it went to zero, however in the last 1/2 mile it was back up to the correct reading. Seems like a ground issue still. What other grounds should I check?
 
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Old Jun 20, 2020 | 10:52 PM
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Try using the 5V feed (black/green tracer) that seems to work ok on the temp guage - see if it makes any difference. I think all the 5v Feeds to the guages are all piggybacked to each other.
Is your speedo. the round style or sweep style/custom cab?
 

Last edited by third66go; Jun 20, 2020 at 10:53 PM. Reason: typo
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Old Jun 21, 2020 | 05:36 AM
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There are only 2 ground points for the fuel gauge. One from the ICVR attaching screw to the brace for the steering column and one from a sender bolt to the brace behind the tank. If you have crimped on terminals instead of soldered check them all to make sure one hasn't been crimped on the insulation instead of the wire.
 
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Old Jun 21, 2020 | 08:41 AM
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Since swapping was a 2 minute try I went and did it this morning and it changed nothing. I looked to see and I did not find any crimps on the insulation
 
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Old Jun 21, 2020 | 09:50 AM
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Gauge testing

Originally Posted by 1966F100SC
Since swapping was a 2 minute try I went and did it this morning and it changed nothing. I looked to see and I did not find any crimps on the insulation
I have typed all this before so to save time I just scanned a couple of pages from the 72 car shop manual. All these gauges are King Seeley type they all work exactly the same, doesn't matter what they are measuring, fuel level, temperature, oil pressure. So this test works for all the gauges. There are some differences in the wiring from the ignition switch to the ICVR from model to model but from the ICVR to the gauge they are all the same.
Grounding one of these gauges at the sender tells you noting except the needle will move and is not the way to do it. These gauges are so sensitive to voltage that the tiny amount of voltage from an analog ohm meter will move the needle.


 
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Old Jun 21, 2020 | 11:42 AM
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Pulled the gauge and did the test of measuring resistance and it stayed within the 10-14 ohm range as instructions said it should. So gauge is good?
Ivr just now tested, pulses 5v as it should
 
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