Fuel Gauge Problem

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6pakattack

6pakattack

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OK, I give up !! I have had a couple different sending units w/floats replaced, and I've got New Circuit boards behind the Dash ! WTF is wrong with this damn thing ?

I'm working with a '69 Dart GTS 340 Auto. Right now my gauge reads EMPTY. I'd be willing to bet, just as I've done in the past that I go down and fill up the tank I may put 4 gals in it ! Bamm, now it's sitting on FULL ! I've had professionals test the Resistance and found ohms reading the wrong way when full, and vice versa ! So even the Pros aren't able to get it right ! It's driving me nucking futs !!! Previous owner did have a fuel gauge in the cluster of three, and I suggested they check to make sure that it was disconnected so it was causing a grounding problem,not sure if they did that or not though ! Any ideas ??
 
Right now my gauge reads EMPTY. I'd be willing to bet, just as I've done in the past that I go down and fill up the tank I may put 4 gals in it ! Bamm, now it's sitting on FULL ! I've had professionals test the Resistance and found ohms reading the wrong way when full, and vice versa ! Any ideas ??
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(1) have a helper in DR seat (2) you underneath & pull L connector off of the sender threaded stud (3) have helper turn ign key on (4) gauge should stay on E (actually left of E a bit) (4) you ground the blue wire L connector either all the way up to the batt neg post (best) or at least to a KNOWN frame/body sheetmetal ground & have the helper tell you if the needle swings rapidly toward F & have him holler when it gets close to F so you can pull the connector & stop the gauge before it pegs. this confirms that all is good from the L connector forward & the problem is the sender or its ground path there at the tank all the way back to the battery.
 
Rapid Robert said:
(1) have a helper in DR seat (2) you underneath & pull L connector off of the sender threaded stud (3) have helper turn ign key on (4) gauge should stay on E (actually left of E a bit) (4) you ground the blue wire L connector either all the way up to the batt neg post (best) or at least to a KNOWN frame/body sheetmetal ground & have the helper tell you if the needle swings rapidly toward F & have him holler when it gets close to F so you can pull the connector & stop the gauge before it pegs. this confirms that all is good from the L connector forward & the problem is the sender or its ground path there at the tank all the way back to the battery.
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Thats about the size of it.
Even if you do get it all hooked up and seemingly working it can misread the actual level.
I went round and round with mine over accuracy, even though I physically checked the ohm sweep of the sender and got a brand new matching ohm gauge it still read oddly at different levels (like showing a half tank on the gauge when there was 2/3 of a tank in reality.)

I just needed to know where empty was for the most part, so I took a gas can with me and drove till it ran out of gas, then made a mental note of exactly where the needle was.

One of the best solutions I have seen to date is a calibrator unit that you basically "teach" the needle where it needs to be by adding 1 gallon at a time and enter it into the calibrator until the tank was full, and then after that it knew where the needle was supposed to be at each gallon difference.
I heard they were pretty darn accurate.
 
You can test all you want but the problem lies with the cheap offshore sending units. I don't recall the details but it comes down to the calibration of the sending unit is off.

Don't know if one can be fixed but I resorted to carrying a thin bamboo cane as a dipstick. When the original one in my Valiant quits it will be a sad day.
 
If you are not getting good reading from the sender, it may just simply be bad. To make this as simple as possible, take readings from the insulated terminal to the flange of the sender.

You can get an idea of how the gauge is doing by imitatiing the old shop manual gauge tester, which was simply three resistors and a switch.

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)
 
Beats me how so many never consider the gauge to be the fault. Fact is there is much more mechanical than electrical inside it. Now consider its age and its lifes labor compared to a temp gauge or any other. Can you imagine wear in the instruments movement eventually causing a seesaw effect ? That is what you're looking at. A secondary programmer inline might make that needle stand at one or more positions between full and empty for some length of time. Good luck with it.
 
Thanks for your replies, at least they give me some where to begin looking myself !
 
TylerW said:
You can test all you want but the problem lies with the cheap offshore sending units. I don't recall the details but it comes down to the calibration of the sending unit is off.

Don't know if one can be fixed but I resorted to carrying a thin bamboo cane as a dipstick. When the original one in my Valiant quits it will be a sad day.
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Quality Control standards for these off shore units is if it reads Full when the float arm is in the full position and Empty in the empty position, it's good to go. Doesn't matter what happens in between. That would take time and time = $$$. So, you can get lucky and get a good one or not.
 
I had same problem with sending unit. When I installed new sending unit along with new Auto Meter gauge, it wash way off. When tank was full, gauge showed full. Drive about 50 or 60 miles and gauge would drop off to 3/4, then go another 40 miles and gauge would drop to empty. Go fill the tank and only would take 9 or 10 gal. to fill it up. Now I gave up on trying to get the gauge right after 2 new gauges and 3 new sending units. Now I just set the trip meter to 0 and look for a gas station at 150 miles. Then fill up and reset trip meter.
 
68 Rat Rod said:
I had same problem with sending unit. When I installed new sending unit along with new Auto Meter gauge, it wash way off. When tank was full, gauge showed full. Drive about 50 or 60 miles and gauge would drop off to 3/4, then go another 40 miles and gauge would drop to empty. Go fill the tank and only would take 9 or 10 gal. to fill it up. Now I gave up on trying to get the gauge right after 2 new gauges and 3 new sending units. Now I just set the trip meter to 0 and look for a gas station at 150 miles. Then fill up and reset trip meter.
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Since you have an autometer gauge, did you check the resistance range of that gauge? I don't think they are 73-10 like the factory Mopar ones... Just a thought.

Sorry no help to the original poster as I have an aftermarket gauge with matching sender.
 
68 Rat Rod said:
I had same problem with sending unit. When I installed new sending unit along with new Auto Meter gauge, it wash way off. When tank was full, gauge showed full. Drive about 50 or 60 miles and gauge would drop off to 3/4, then go another 40 miles and gauge would drop to empty. Go fill the tank and only would take 9 or 10 gal. to fill it up. Now I gave up on trying to get the gauge right after 2 new gauges and 3 new sending units. Now I just set the trip meter to 0 and look for a gas station at 150 miles. Then fill up and reset trip meter.
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I had the same problems with mine when i got it turns out the aftermarket gauge was for a ford hence when it was full it read empty and empty read full.

to the original problem tho you could always look at for the point of view that E is for enough
 
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