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Testing gas gauge sending unit

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Old 11-07-2018, 10:54 PM
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Question Testing gas gauge sending unit

What is the procedure for testing a gas gauge sending unit, with it out of the tank?
 
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Old 11-08-2018, 12:25 AM
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its just a variable resistor so you can ohm between the wire and the body of the unit move the float up and down see if its a open circuit or changes resistance
 
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Old 11-08-2018, 03:55 AM
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Is there some sort of chart for this to show at what ohm it should be at full, halfway and empty? Just wondering for personal use, slowly mine has degraded so 1/2 full on the gauge means full tank.
 
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Old 11-08-2018, 09:19 AM
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Im sorry I canít help ya with ohm values . Take the wire coming to the fuel sending unit ground it to check the gage in The dash it should go all the way over past full I have seen a couple of those to be bad also
 
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Old 11-08-2018, 06:16 PM
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I believe officially the reading should be 10 ohms full, 90 ohms empty. But that can vary from sending unit to sending unit, you will probably find 70ish ohms will give you a empty reading. None of these things are exact, different trucks read differently, they have their own personality as far as fuel readings. They all should be in the ballpark though.
 
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Old 11-08-2018, 06:42 PM
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Good thing I got dual tanks, as soon as it stutters, flip the tank selector
 
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Old 11-09-2018, 04:31 AM
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This seemed helpful:
 
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Old 11-09-2018, 09:46 AM
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Originally Posted by crucialprospect View Post
Good thing I got dual tanks, as soon as it stutters, flip the tank selector
If you happen to have a trip odometer, I have found that works well to keep track of fuel usage when your gauge doesn't work.

You need an idea of how large your fuel tank is, or how much fuel you usually put in it. Set the trip odometer to zero at the fuel station and fill it up. Drive it for 250 miles according to the trip odometer and then go to the station and fill it up again. If you normally put 13-14 gallons in it when it's empty, but at 250 miles you only put 9-10 gallons, reset the odometer to zero again and then drive 275 miles or 300 miles, however much you dare, and then fill it up again and see how much fuel it takes.

You will get it zeroed in on how many miles you can go on a tank. You just have to remember to zero the trip odometer each time you fill it up at the station. It actually is easier than it sounds and is very accurate,
 
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Old 11-09-2018, 12:40 PM
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Now your making me feel real bad, I donít think I can get 250 miles with both tanks full!

but that is a good idea, thanks for the suggestions!
 
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Old 11-09-2018, 02:11 PM
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I was using this method on my 2.9 v6 ranger when the sending unit went bad. It has a 16 gallon tank, I would go 300 miles and then I was able to put 13-14 gallons in the tank. Never had a problem. I finally repaired the sending unit, and now when the fuel gauge is on empty, I go to the station and can only get about 11-12 gallons in it. I have been doing my trip odometer trick even though I repaired the gauge, and when the gauge gets to "E", I am only about 260 miles in. So that shows you how conservative sometimes the gauge readings can be. But it is probably better to keep more fuel in the tank to keep the pump cool.
 
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Old 11-10-2018, 10:10 AM
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Originally Posted by Franklin2 View Post
If you happen to have a trip odometer, I have found that works well to keep track of fuel usage when your gauge doesn't work.

You need an idea of how large your fuel tank is, or how much fuel you usually put in it. Set the trip odometer to zero at the fuel station and fill it up. Drive it for 250 miles according to the trip odometer and then go to the station and fill it up again. If you normally put 13-14 gallons in it when it's empty, but at 250 miles you only put 9-10 gallons, reset the odometer to zero again and then drive 275 miles or 300 miles, however much you dare, and then fill it up again and see how much fuel it takes.

You will get it zeroed in on how many miles you can go on a tank. You just have to remember to zero the trip odometer each time you fill it up at the station. It actually is easier than it sounds and is very accurate,
I do that more so on my work truck (big rig) as I don't trust the gauge. When it gets close to 400 miles I start looking for fuel.
Thing is if running short run say around town the gauge reads lower at say 300 miles than it does if running long high way runs where I have gone 426 miles and still felt safe to go more if I had to.
On my DD I did it more to track MPG up to the last 3 fill ups. When they all were pretty close to each other I did not see a need any more. Besides I trust the gauge a lot more than the work truck one.

I think this weekend if I get out to the garage I will check if the 2 senders & gauge if it works in my project truck as I have not put fuel in either tank yet. Truck is no where close to getting on the road and don't want the gas to go bad sitting, I run it off a small can on the fender well.
Dave ----
 
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Old 11-10-2018, 11:52 PM
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The '78's readings would be 10-70 ohms (or more precisely, they were something like 9 to 73 or something like that) but Ford changed the range on gauge senders at some point. So the '87 might be the new style.
I'm sure it's written down somewhere. Otherwise what everyone has said.
Even my original factory Bronco senders both were incorrectly matched to the gauges. I ended up tweaking both the stops and the arms to get them to read properly. Or at least "properly" based on what I wanted them to read.
Both my F350 tanks read just the way I like them to. Just a tick above the full line when full of gas, and a couple of needle widths below empty when it chugs to a halt.
When just reading empty I have a few gallons left. Just the way I like it.

Paul
 
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Old 11-11-2018, 08:30 AM
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1987-up are different. Instead of low ohms full, high ohms empty they are the opposite, low ohms empty, high ohms full. Not sure of the exact ohm readings for the later gauges. But they are setup more like the style GM uses. You will notice the older gauges always go to empty when the key is turned off, raise up when the key is turned on. The GM style and the 87-up Ford style gauges sort of just sit where they used to be the last time the key was turned off. They do not use the 5v instrument cluster regulator like the older setups do.
 
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Old 11-11-2018, 05:07 PM
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After a painful experience of changing my body bushings , I drop my tank. (1985 f1504x4) ,Seems my brass float was full of gas and replaced it with another brass float ordered from Summitts.. With my model I checked it, key on,- sender hooked to connector and manually operated it. Good luck TR
 


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