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Inaccurate Fuel Gauge

69 R/T

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Howdy, Here's my problem, I hope someone can assist. My 1969 Coronet has a restored fuel tank and new sending unit, however the gauge never reads past half full when completely filled. I haven't crawled under there yet as I've been very busy with other things. The car has a newer paint job so I'm thinking possibly a grounding issue...but if it's not, then?

I just bought this car, so I'm not sure about anything done to it aside from the fat stack of receipts. Thanks to all who respond. Ted
 
Most likely the float is not properly adjusted and is only coming up half way when the tank is full. The only way to know for sure is to drop the tank, drain it and remove the sending unit. Then check the sending unit by leaving it plugged in and manually raise the float to the upper limit and checking how the guage responds. Then drop it to the bottom of travel and see if the guage shows empty. You can also do a resistance check on it with a VOM if you suspect an electrical problem. The jumper that goes between the the rheostat part of the sender (part that is in the tank) and the collar sometimes builds up more resistance due to age and corrosion. This was one problem I had with mine.

Finding the fuel ending units for these cars is not easy and while seraching for one for my 78 Magnum I got at least 6 different part numbers from various vendors. When they sent me pics of the items none were the correct part. I ended up rebuilding mine myself and have gone through a tank and a half of gas since the rebuild and it gives the correct tank level just fine.
 
Yep. What he said. Could be the arm the float is attached to is bent wrong and is contacting the top of the tank limiting it's travel. Could also be the float has a leak and has fuel in it.
 
the aftermarket sending units use GM resistance 90-0 instead of 70-10 like the mopars... which makes the gauge read incorrectly.
 
the aftermarket sending units use GM resistance 90-0 instead of 70-10 like the mopars... which makes the gauge read incorrectly.

Is there a correction for this ? I am pretty sure there is no adjustment on the fuel gauge. Do we just have to live with this problem. My 67 GTX has the same problem and I went thru two units from Year One & neither reads correctly.
Is the simple answer to bend the float arm till the empty reading is correct & live with whatever it read when full ?

John :confused:
 
I've also noticed that many of the newer aftermarket sending units use a white plastic float, rather than a brass float like the originals were. Is the plastic float the GM unit that was talked about above and could the problem be fixed by using the proper brass float?

Another problem with reading errors can be caused by a bad, or dirty sending unit ground strap.

Richard
 
I don't know why the material the float was made out of would make a difference. Buoyant is buoyant.

i think
 
I was just wondering about a possible weight difference between the two materials?

Richard
 
I'm sure there is some, but I doubt it would matter. However....if you have the plastic and want the brass float, it can be had at your local Ford dealership.
 
Are the Ford units any different from ones sold by various Mopar aftermarket retailers? I bought a new 3/8" sending unit a few months ago for my Coronet not realizing that it had one of the plastic floats, so I bought a brass float from Van's Auto that I will replace the plastic float with before I install the new sending unit into my new fuel tank.

Richard.
 
Is there a correction for this ? I am pretty sure there is no adjustment on the fuel gauge. Do we just have to live with this problem. My 67 GTX has the same problem and I went thru two units from Year One & neither reads correctly.
Is the simple answer to bend the float arm till the empty reading is correct & live with whatever it read when full ?

John :confused:[/QUOTE
I've never came across that in 48 yrs of mopar. Checking the gauge is easy With the key on have some one watch the gauge while you unplug and ground the sending unit wire. If it goes to full the problem is the sending unit. You can get them on ebay for 49 bucks and they are 70-10. 99.99% of the time this problem is a leaking float. That's an easy fix if you have a burner of some kind outside. Put the float in a empty pan and heat it, the gas will evaporate out. Then re-soldier the seem.
 
I've used many of the Ford floats and they are just the right thing. If I had to make a guess, I would guess that it's the brass float that everyone is selling. They're about $6 at Ford I think
 
A float is a float. Makes no difference if it's brass or plastic.

My understanding is that Chrysler switched to plastic because of today's gas. It's too corrosive for the brass and eats through the solder quickly. I was told this by the company that makes the sending units for Chrysler currently, including the old ones they still carry. Maybe it's BS, I don't know.

Either float performs fine on the sending unit. It's just a matter of preference.
 
My dart is the opposite, When it reads 1/4 tank left, I'll stop and put in 4.5 - 5 gallons and it's full, so it's about 1/2 a tank off.
 
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