Gas Guage Works with the Sending U Out of the Tank

[money pit]

I have a 70 Barracuda. My gas guage reads a quarter to a half a tank after I fill up. I tried replacing the sending unit (an OER unit). The samething happened. I have a ground to the sending unit, directly from the battery. I tried both sending units outside of the tank, both seem to work fine. When I place the units back in the tank, they read the same as before. I checked the sending units with an Ohm meter,   it's within specs. I know the guage works, I grounded the lead, it pegs the guage. Could there be something in the tank that is interferring with the sending unit?  This is driving me crazy.  Thanks. 

[70chall440]

To answer your question, yes there could be depending on what style tank it is. There were a variety of tanks and some of them had some internal lines that might be blocking the float. This isn't really a super likely scenario but it seems like you have eliminated most everything else. What I would do is pull out the sending unit, try and get a camera or flash light and mirror or something and look in there. If you have access to a fiber optic camera you might be able to get it in there to see, or drop the tank and check it out.

[money pit]

The tank and the sending unit were in the car when I bought it (the tank looks new). I had the floor of the trunk replaced so the tank was removed. It was working for a while then stopped. This car was a slant six originally. I have a 360 in it now, if that makes a difference.  Thanks. I drain the gas and look in the tank.

[70chall440]

None of that should really matter (previous /6). The nice thing with a Cuda is when you get it out because of where the fill tube is, you might be able to actually see the sending unit and float. I would mock it up out side the car and see what the deal is, you can pour water into it so get the float to move, just have to completely drain it and dry it out before reinstalling it.

[JayBee]

There was a mod that went around sometime ago that might help. Unfortunately most pictures are gone due to Photobucket.
http://www.cuda-challenger.com/cc/index.php?topic=67680.0
Also, are sure that the float is 100% empty.

I added a couple pictures of that mod that were saved on my HD. 

[money pit]

Thanks, the pic really help.  I appreciate your response.

[money pit]

Does it matter what gauge wire you use? Also, is that a solid core wire you used?  Thanks

[JayBee]

I don't think it matters what gauge, I would think the thinner the better for flexibility. IIRC I used multi-strand 18 gauge. Mine's the lower picture, top one I took off the web and edited it with the arrows.

[70chall440]

18 gauge is fine, you don't need anything heavier than that (like 12,8, etc.) as that wire does not see a lot of amperage. You could probably get by with even 20, but that starting to get a bit small for my liking.

You should not be using any solid core wire in your car, not that it will create any real issues but solid core is usually reserved from building and industrial wiring. All vehicle wire is usually multi strand copper wire. There are a lot of "types" but anything you get from an auto parts store should work fine.

[stu in wichita]

Plus, solid wire is too stiff and won't permit free movement of the float arm.  It needs to flex, so make sure that the arm will move through its full range without binding.  I just did this modification a couple of days ago and used some power tool brush connection wire - super flexible.  Sadly, it didn't correct the problem. 

-Stu 

[money pit]

Thanks. In the upper photo I couldn't tell if that was a solid core wire. It looks like a bare wire. Will gas break doen the insulation of the wire? Your photo looks like the wire has insulation. I have an extra sending unit that I can make the modification.  Thanks again

[JayBee]

Will gas break doen the insulation of the wire?

I never noticed any insulation breakdown on mine when I finally had to replace it. The sweeping arm inside it actually fell off.

It looks whoever did the top one stripped the insulation off.

[money pit]

Thanks. Your response is the only one that mentions this modification. I searched on 3 different E Body forums.

[70chall440]

it works, I have had to do it too.

[JayBee]

Thanks. Your response is the only one that mentions this modification. I searched on 3 different E Body forums.

Personally, I'm only on one other ebody forum and don't recall mentioning it there. I found that mod from a Google search that, I believe, lead me to a Moparts link.