I've searched the forums and did the preliminary troubleshooting. My fuel gauge only goes to between 1/2 - 3/4 when the tank is full. The gauge moves toward E as I drive but I never know how much gas is left in the tank and it makes me nervous. The tank and sending unit are new. The gauge pegs full when I ground the wire. My neg battery cable has a good ground to the block and my block to firewall ground wire is new and well grounded. From what I read in the archives, my float arm may need to be adjusted. Is there a good procedure for doing this? Is it possible I don't have the sending unit properly oriented? The line coming out of the tank is at the 5:00 position and points at an upward angle to about the 2:00 position. One last detail: when I got the car, the wire inside the trunk was damaged in a couple of placed so I cut out about 2' of it and replaced with new. Any advice will be appreciated.
Adjust Fuel Sending Unit?
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brianj5600
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Edit: Oops I skipped the part about it being new.
It may have fuel in the float. Mine did the same thing. You can get a new float for less than $10. Get a new gasket while you are at it.
It may have fuel in the float. Mine did the same thing. You can get a new float for less than $10. Get a new gasket while you are at it.
golf4283
Active Member
What year gas tank did you install? It's possible that f you have a 69+ tank that maybe they gave you the 65-68 sending unit which wouldn't read correctly cause the earlier tanks were smaller.
I put a '70 tank in my 66 and if I wouldn't have changed to a '70 sending unit my gauge would have read uncorrectly too.
I put a '70 tank in my 66 and if I wouldn't have changed to a '70 sending unit my gauge would have read uncorrectly too.
Thanks for the idea, but it's a 16 gal tank. I've been searching the net this morning and based on some pics posed in the "How To" section of Mustang Monthly's site, I think I may have the sender in the wrong position. On their site, the stem looks to be in the 6:30 position, while mine is in the 5:00 position. I'm going to drain the gas, pull out the sender, check the ohms readings at each end of travel, adjust (bend) if necessary, then re-install in the position I saw in the pic. I'll post my results later.
And now, the rest of the story...yesterday I drove the car until I was on E. This afternoon I put it on jackstands, drained the tank which had just over 4 gallons. Mind you, the gauge was on E. I pulled the sending unit, checked the range of travel with an ohm meter. .09 @ full, .76 @ empty. Close enough to the .10 - .73 range it was supposed to be. I then connected the wire, grounded it to the tank, taped the float arm to the E position and watched the gauge, then taped the arm to the F position and watched the gauge. At full F, the gauge only travelled to just over 3/4 position. I bent the arm to get it where it read exactly F and E with the arm in the proper positions. It took a couple of attempts but I got it. At this point I'm feeling pretty good about things. I put the sending unit back in the tank, then I started filling it one gallon at a time. After each gallon I checked the gauge and recorded the position. To make a long story short, it took 4 gallons to get the needle to slightly pass the E mark. Each additional gallon moved the needle closer to the full mark but always to a point less that I would expect with the gallons added to the tank. As I was pouring in the 14th gallon, gas started backing out the filler. I looked down the neck and gas is right there...full as could be. Either there was still gas in the tank when I drained it (the plug was out and the front was lower than the rear) or my tank isn't a 16 gallon tank. At this point the gauge reads barely over the 3/4 mark. I'm really no better off than when I started, except now I know there are almost 4 gallons in the tank when reading E.
I'm not exactly sure what to do at this point other than go through this whole drill again some day except I will bend the arm so in the full F position, the gauge reads way over F. Then maybe it will start registering on the gauge with less gallons and maybe it will move to the F position when full.
What do you make of me only getting 14 gallons in the tank and it being full into the filler neck?
I'm not exactly sure what to do at this point other than go through this whole drill again some day except I will bend the arm so in the full F position, the gauge reads way over F. Then maybe it will start registering on the gauge with less gallons and maybe it will move to the F position when full.
What do you make of me only getting 14 gallons in the tank and it being full into the filler neck?
golf4283
Active Member
I'm thinking 2 things.
-Your 40+ year old gas gauge needs replacement or
-your using the wrong year fuel sending unit. Now I thought about it and i'm beginning to think you have a fuel sending unit from a later year car in your earlier year car. That would be why when your tank is full it still only reads 3/4 full. If I were you I would do the test and bend the float downward towards the bottom of the tank. This in turn will make up for the excess lift that is needed to get you to E as well as maybe getting it to F. I say try that out.
-Your 40+ year old gas gauge needs replacement or
-your using the wrong year fuel sending unit. Now I thought about it and i'm beginning to think you have a fuel sending unit from a later year car in your earlier year car. That would be why when your tank is full it still only reads 3/4 full. If I were you I would do the test and bend the float downward towards the bottom of the tank. This in turn will make up for the excess lift that is needed to get you to E as well as maybe getting it to F. I say try that out.
I'll have to look back at my invoices to see which sending unit I ordered. It's possible I was sent the wrong unit. I'm going to do as you suggested and bend the arm further down to try to compensate for the the "slop" I now have. Of course, I need to burn through the full tank of gas I now have. The weather in Upstate NY is starting to change so I should get a few days to empty the tank.
golf4283
Active Member
golf4283
Active Member
even if you ordered the right one I wouldn't put it past a distributor to mistakenly send the wrong one. I don't believe however that this can be fixed with just bending the wire since the later years sending units have a wider range of travel because the gas tank is higher up.
Using this logic when your tank is empty it will still read probably between 1/4 and E.
If you want I have a fuel sending unit from my '66 tank that I replaced with a '70 tank and sending unit. I can send you it if you want to see if that will work. I'm just gonna toss it out if not.
Using this logic when your tank is empty it will still read probably between 1/4 and E.
If you want I have a fuel sending unit from my '66 tank that I replaced with a '70 tank and sending unit. I can send you it if you want to see if that will work. I'm just gonna toss it out if not.
It's not a problem draining the tank but it's full up into the neck. I don't have enough empty gas cans to take all that gas. Plus, it'll be more fun to drive it to empty! Rather than you going to the trouble of mailing your old sending unit, I think I'll try to get the specs on the early vs later sending units to try to figure out which one I have. Thanks for the offer and I appreciate all the feedback.
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