1969 Mach1 fuel gauge will not go past 1/4 full

dave0z · Dec 18, 2006

I have a 1969 Mach 1 with 351W. The gas tank was installed by previous owner and the fuel gauge never worked properly since I got the car 2 years ago. I installed a new sending unit recently thinking it was the problem, but the original dash style gauge never goes past 1/4 full. Can someone help explain a fix for this problem? Is it a grounding problem or possibly just an old wiring problem? Thank you.

69 Rustang · Dec 18, 2006

Grounding can be a problem--happened to me. After running out of gas for the second time in less than a week due to a combination carb problem and an inop gas gauge--we connected a good ground from the sending unit to the frame and the gauge worked perfectly. Fortunately my Dad was semi-retired when that happened and he served as "roadside assistance" with only a minor bit of grumbling and lectures.

grego37 · Dec 19, 2006

those things work off of proper ohm ranges. but if you have the factory gauge and a factory/aftermarket stock style sender they should work together.
are you sure the sender is in properly, maybe its in 180 degress off and the float is hitting the side of the tank, maybe there's only one way to install it, i forget?

once you rule out the sender, yes check all grounds, if those are good see if gauge needle is stuck on something, if still no luck, i'd guess the actual gauge went bad?

gregp1962 · Dec 19, 2006

I've had about 7 classic Mustangs in my life. One of them had a gas gauge that worked.

69 Rustang · Dec 19, 2006

grego37 said:
are you sure the sender is in properly, maybe its in 180 degress off and the float is hitting the side of the tank, maybe there's only one way to install it, i forget?

There is a tab on the sender and a slot in the tank mounting area to ensure the sender gets "clocked" properly. Not saying someone couldn't remove the tab or a cheap Taiwan sender may not have it...

Testing the OHM range is a very good idea to trouble shoot this further--you will have to search the forum but someone has posted the proper readings you should get. Hooking up a test lead to the sender and frame to check for ground is a simple first test with the ignition on and someone watching the gauge.

geostang351 · Dec 19, 2006

69 Rustang said:
Testing the OHM range is a very good idea to trouble shoot this further--you will have to search the forum but someone has posted the proper readings you should get. Hooking up a test lead to the sender and frame to check for ground is a simple first test with the ignition on and someone watching the gauge.

73 Ohm empty/ 8-12 Ohm full. For most Fords before 1989.

69gmachine · Dec 19, 2006

You may also need to bend the lever with the float down so that it go through the full range of motion when installed. The last two replacement sending units I installed both needed to be bent to travel through the range properly.

RGS0907 · Dec 20, 2006

69gmachine said:
You may also need to bend the lever with the float down so that it go through the full range of motion when installed. The last two replacement sending units I installed both needed to be bent to travel through the range properly.

...and you have to do it through trial & error. That means draining the tank each time & pulling the sending unit out & bending it just a little bit at a time. What a PITA! I even had a repro unit that was pouring gas out through the element. After my wife theatened to push my car into the street because of the gas fumes in the garage, I finally rebuilt my 40 year old OEM unit & reinstalled it.

1969 Mach1 fuel gauge will not go past 1/4 full

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