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Discussion Starter · #1 ·
next question:
The fuel gage is still not reading correctly in my 86.

New sending unit
New gage.

Made sure the fuel tank and sending unit are grounded real good.

First got no reading.

After driving, and filling it up, got a half tank reading for a while, went to 3/4 for a while. Drove it a while now back to near empty, but should have at least half a tank.

I know I have posted this several times over the past couple of years but I'm ready to pin this thing down.

Any suggestions?


thanks
 

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Discussion Starter · #3 ·
I'm asking this question again in hopes that someone will have had the same or similar issue.
The gage is still erratic.
I have a ground from battery to the negative on the sender to make sure it is getting a good ground. The under dash grounds seem to be fine and all lights and other gages work fine.
The gas gage will go down to E after about 100 to 150 miles. Might hold 10 gallons maybe 12 or so sometimes, but I won't let it get empty. If I fill the tank full, all the way to the brim, I may drive 25 to 50 miles before anything registers on the gage, then the gage will jump to 3/4 full. I can drive around a day or two 50 to 100 miles or so and the gage goes gradually down to half full then maybe 1/4 and usually quickly to E again. Then the cycle starts over again. It is too inconsistant for it to be a intermittent ground or something like that I think but ??????:dontknow:.
Anyway, it seems like a faulty sender to me but it is too much like the sender I replaced and the other question in my mind is, is the sender bad possibly. I'm almost 100 percent sure it is a 16 gallon tank and that is the sender I ordered. Any thoughts???? I haven't checked the ohms at the gage yet.
 

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17 Or 22 Gal?

They had two different tanks available. A 17 and 22 gal. tank. First you need to know what tank you have. They made two different sending units, One for 17 and one for 22. That could be your problem.
 

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Discussion Starter · #6 ·
I'm almost positive its the 17 gal. I have never put more than 16 or so in it. I will check the build codes in the glove box and if necessary, run it out of gas but the strange thing is the old sender started doing basically what this new one is doing. I replaced it and it does the same thing. Replaced the gage also.

I should have said it is consistent in what it does, not inconsistent. It is really acting weird.
 

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Discussion Starter · #7 ·
is there a build code for the gas tank size?
 

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If I fill the tank full, all the way to the brim,
I may drive 25 to 50 miles before anything registers on the gage, then the gage will jump to 3/4 full.
if the new sender does the same as the old one??
I would check the power to the gauge..
loosing power would let the gauge die or stick in one place for a while, then move again..

the only difference the sender for the other tank would make is where empty is
and ether one can do that if not adjusted right..

it would not make it stay in one place for a long time, except when full..

:texas:
 

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Discussion Starter · #9 ·
yeah and it sticks on empty more than anywhere? But I don't see the gage move like power is coming and going which you would expect.
 

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I have the same problem on my 65.
New sending unit.
Rewired everything
checked gauge to make sure its working correctly.
Only thing I can think of is that the sending unit is set for the wrong ohms or the positive lead on the fuse box is not 12 volt (it's wired to a fuse block called gas pump right now} or there is still a bad ground somewhere.

My problem is that the tank never reas more than 3/4 full. But if I disconnect the positive lead the gauge will go past full. This is how you know you have a good ground and that the gauge sweep is working correctly.

Honestly seemed like an easy fix, but it's not. :(:dontknow:
 

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Discussion Starter · #12 ·
I will be checking the power to the gage and sender, that is the only thing left, other than the sender needs adjustment or something like that. Thanks for the ideas.
 

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Testing the dash gauge is simple. Tank unit is a 0-100 OHM rheostat. You can make the gauge move in increments using an old sending unit or buy a few resistors. Grounding the sending unit wire is 0 Ohms so that would bring the dash gauge to empty. 100 Ohms is full, an open wire makes the gauge go past full.
 

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ok if the gauge is reading near empty? then you have either a sending unit that has the float Hanging wrong, as in to high, or you have a bad wire from the tank to the dash. I'm a little foggy here, but I believe that GM used a flat ribbon wire that runs through the cabin to the dash??? I have seen those get rubbed bare on the bottom side and cause intermittent issues most common is blowing dome light fuse. this wire could be caught, pinched or just worn. I did see one get caught under the foot of the front seat. I would suggest maybe run a wire from the sender to the (head) of the ribbon cable, and remove the ribbon from the equation. at least for a test.

if memory serves me right a rubbed ribbon was the problem on a 1987 Caprice wagon I once had.

P.S. have you pulled the dash and made sure the printed circuit board is ok, no breaks or burns?
 

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I think Tinbender59 maybe on the right track. You may (have fun doing this) need to trace the send wire front to back looking for a bad spot in the wire. You could try ohm it but if its intermittent???
Good luck

Eric
 

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Measure your tank to find the number of gallons it will hold. Length x width x height will give you the capacity in cubic inches. Multiply the total cubic inches by .004329 to determine gallons. You should be able to come close enough to determine if its a 17 or 22 gallon tank for sure.
 

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Both tanks are the same dimensions. Just a different location for the filler neck.
 

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Since volume is determined by dimension that makes no sense to me. A quick google tells me that a GM 17 gallon tank is 36 1/4 x 24 1/4 x 8 7/8 and a 22 gallon tank is 38 1/2 x 25 x 10 3/4. Now that makes sense to me. But I don't pretend to be the sharpest knife in the drawer. :dontknow:
 

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Any vessel, gas tank, aquarium or beer mug with those dimensions will hold 33 gallons unless limited by other factors (wall thickness, air space, baffles, etc, etc, etc.) It is limited to 17 gallons only by design. Unfortunately, none of this helps solve Harpman1's gauge issue. My gauge shows a tank and a half all the time so I understand the frustration of not knowing how much fuel you have.
:secret:
 
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