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Discussion Starter #1
Hey everyone, I recently got a 66 Mustang coupe and had the seller's mechanic install a new sending unit for the fuel gauge. However when I went to fill up the tank, the gauge only went up to a little past the 1/4 mark. So it's not reading the tank accurately. The gauge clearly works because it moves when I start the car and it did go up after I filled up, but only past the 1/4 mark. I initially thought that maybe I didnt fill the tank all the way, but I confirmed it was full because I could see the gas. Any diagnostic advice?
 

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You have learned the secret of the aftermarket fuel sending units. They are notoriously inaccurate and complete junk. There is a sending unit made by ACP that is closest to original.


I notice that you have some sort of aftermarket gauge. The original Ford gauge and sending unit was designed to operate in a range of 10-73 ohms resistance. Your gauge may be designed to work within a different range. Later Ford and all GM sending units and gauges operate within a different resistance range.
 

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Discussion Starter #4
Correct awhtx. The reason why I had the seller fix the gauge was because the gauge wasnt working at all due to not being compatible with the sending unit in the car. So they replaced the sending unit to make it compatible with the gauge that I have. The gauge works, it's just inaccurate. I still have the receipt from the work done which was a week ago, but the mechanic is an hour drive from me. I wanted to see if this may be an easy fix.
 

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You could bend the wire/rod on the sending unit so that sends the correct current to the gauge. Mine reads about 1/8 of a tank low when full, but I am OK with that as when it hits E, I know I still have a little left. The fix for mine would be to empty the tank, remove the sending unit, bend the rod so the float is a little lower. Making the float lower raises the wiper arm (Actually, I think it lowers it as it is on the opposite side of the pivot) on the sending unit which in turn will tell the gauge there is more fuel in the tank. Now the trick is, does it match when you have 1/2 tank, or when its empty?

 

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UH, He's also using a Non-Original Aftermarket Fuel guage....so with that being said, In using a stock Fuel Sender... The reading will most likely be off anyway...

Only way that he can fix it is drain the tank , and pull out the sender and keep bending the Float arm either way until its most accurate.. It might take him a few tries as well I might add... and may never be 100% accurate... Just thought that you should know.

:eek:)

Tony K.
 

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I used NPD's better sending unit - its still off by a 1/4 - not worth the effort to remove it and bend the arm - the joy of using aftermarket parts.
 

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I’ve been through the gamut of sending units, and I finally found that the Tanks Inc. senders actually work with the stock gauges...or close anyway. The only way to make it close to perfect with a stock gauge is to pull the instruments out, pull the gauge out of the cluster and when the tank is full, you need to adjust the “high-side” cam on the back of the gauge to show full, then when empty you adjust the low side accordingly. The gauge needs to be powered (IVR plugged in), and you’ll use a small flat-blade screwdriver to turn the cam. You can also do this with the sender out and the float arm at the raised and lowered positions, but in the tank, the actual fuel levels may not be exactly on these extremes, so you may still be off some.. These were clearly designed to be calibrated, though the procedure is not outlined in the shop manual. With an original sending unit that works, these were apparently preset for proper operation, with an aftermarket one, you have to tune it. The aftermarket gauges that are reproductions of the originals have the same adjusters, so hopefully this will work for you. Easy job, just a pain to get to it in the first place.

Now, to get one that doesn’t leak! ?
 

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Another possibility is if the mechanic was not familiar with original 1966 mustang gauges, he might have wired the new aftermarket gauge in using the IVR as the power source. Every aftermarket gauge I know of requires a full switched 12 volts wired to it.
 

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On my aftermarket sending unit I bent the float arm such that it reads pretty accurate at empty. The minor downside is when the tank is full it reads at 3/4 full. Once the gas goes down to 3/4 full it will read pretty accurately from that point on down to empty.
 

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I suspect Bsolo is correct. You need to find a manual for your gauges and see what power is required and what type of sender. If your guagua is supposed to have 12v and you are running it off the IVR you will only get 5volts and it will read low. If it does require 12v you need to be sure it is compatible with your sender. Ford senders were designed for the 5 volt IVR.

If you ave the correct wiring and it is still off.p, you can invest in a Meter Match. This little box allows you to custom match the sender output to your gauges scale. It’s specifically designed for running aftermarket gauges in a classic car.
 
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