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Fuel gauge


jgreg53
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Pull the sender out of the tank and hook it to the dash gauge . Move the float up and down while watching the gauge . Be sure to ground the sender . That might help to get an idea of what is happening . Look for any frayed wires . 

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Interesting. I think I just encountered a similar situation. My 51 Cambridge is very new to me (1 week) so I don't know the vehicle very well yet. On Saturday I was looking for a gas station near me that sells ethanol free gas because my fuel gage was just under 1/4 tank. Pulled up to the pump, shut it off and filled the tank. But then it wouldn't start, just cranked over. Checked for spark at the points by manually breaking the contact points - check. Took the top of the air cleaner off and checked for fuel. The road is pretty noisy in that location but I thought I heard a squirt when I moved the throttle.

With no tools tools with me, I was ready to give up can call for a tow truck. But I thought I'd give it one more. It gave a little kick on the first crank so I pumped the gas before the second crank, and she fired. It's been running perfect ever since, and before too.

It seems almost too coincidental the I ran out of gas at exactly the moment I pulled up to the pump, but I guess it's possible. 

Any ideas what this could have been?

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21 hours ago, jgreg53 said:

My fuel gauge was reading a fourth of a tank yesterday as I ran out of gas.  Any ideas?

Was the needle on your fuel gauge bouncing around a bit, or was it steady?

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  • 2 weeks later...

Bouncing around. I took the sending unit out took it apart. First I tested the resistance.  Moving the float made the reading erratic.  I took it apart  to see if anything was amiss. It's a very simple design.  A pointer tab contacts a coil winding as the float level changes. My problem now is the gauge is at three fourth tank and other than fluctuating up and down the level is staying at 3 quarter. I know I'm not getting that much mileage. 

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Your float works like a dimmer switch that sends a current to the meter on the dash. If you remove the sender unit and with a meter set to ohms (resistance) move the float from one extreme to the other slowly. Digital meters do not react quickly. You should see a difference in the reading. Is there a spot where you get no reading?

It might be possible you have a poor connection someplace.

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On 8/1/2022 at 10:22 AM, motoMark said:

Interesting. I think I just encountered a similar situation. My 51 Cambridge is very new to me (1 week) so I don't know the vehicle very well yet. On Saturday I was looking for a gas station near me that sells ethanol free gas because my fuel gage was just under 1/4 tank. Pulled up to the pump, shut it off and filled the tank. But then it wouldn't start, just cranked over. Checked for spark at the points by manually breaking the contact points - check. Took the top of the air cleaner off and checked for fuel. The road is pretty noisy in that location but I thought I heard a squirt when I moved the throttle.

With no tools tools with me, I was ready to give up can call for a tow truck. But I thought I'd give it one more. It gave a little kick on the first crank so I pumped the gas before the second crank, and she fired. It's been running perfect ever since, and before too.

It seems almost too coincidental the I ran out of gas at exactly the moment I pulled up to the pump, but I guess it's possible. 

Any ideas what this could have been?

The fuel pump could be weak.  if the tank is more than a quarter full there is enough pressure from the tank to keep the fuel flowing to the pump, if less gas intank the pump cannot pull itthrough the line.  Another thing that can cause this problem is a pin hole in the gas line.  An old Mustang I had started very hard when I first got it. Once running it was fine.  It never leaked gas either.  Eventually I replaced the fuel line and discovered that the old line had a pinhole where it went up over the axle.  When the car was stopped thefuel would drain out of the line back to the tank and the pump couldn't pull it back over the hump, but once started it would run fine. 

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On 7/31/2022 at 2:49 PM, Jerry Roberts said:

Pull the sender out of the tank and hook it to the dash gauge . Move the float up and down while watching the gauge . Be sure to ground the sender . That might help to get an idea of what is happening

It sounds like you pulled the sender and did a resistance check.

 

Follow JRs above testing so you can determine if the gauge and sending unit are working with the sender out of the tank. I pulled my gauge when doing this test but you can get away with just pulling the sender. Set the sender flange up level on a something that allows you to position the sender float in different positions. Use some extra wire lengths to connect the sending unit wires to the gauge wires. Set the float in a few positions and turn the key on to view the gauge reading in the car. Give it 1-2 minutes to reach the full limit as it may keep creeping up. Check it with the float positioned at half tank, full and toward empty. Make sure the sender has a good ground connection. I found even testing out on the bench that I had to wire brush a spot on the sender to get a good ground before it worked.  Stuff a rag in the sender unit whole to keep things out of the tank and any unwanted sparks from that opening. Picture below may not be identical to your gauge, but you should get the idea of makeshift positioning of sending unit flange and float for testing.

IMG_0562a.JPG.c0e10f03a89850da0c55347b6aae575d.JPG

Edited by Veemoney
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I went ahead and ordered a new sending unit from AB just to eliminate that as the problem. It seems to me the bottom of the unit is constantly soaked in fuel. Couldn't be good for it.

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I believe mine is original to the truck. When I pulled the sender there was no cork float present so I fitted it with the wine bottle cork in the picture and just came back from a ride. So far been a week and still working as it should but will see how long it holds up. Don't throw your old one out till your sure the new one fixes the problem.

Edited by Veemoney
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16 minutes ago, jgreg53 said:

Is it at all possible to use a 12 volt fuel gauge in a 7 volt system?

 

Maybe, the later stock fuel gauges used in 12v Mopar systems don't actually use 12, they use roughly 5v.  The is an Instrument voltage regulator that drops the q2v to work with the gauges, not sure how changing the ground polarity would affect teh needle swing though, probably make it backwards, lol. 

 

Now if you are talking about an aftermarket one, probably not because even with a buck boost setup the grounds are opposite.

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Talking about the fuel gauge, it is always moving when you are down from the full mark, it move with the motion for the car and bumps.etc.. 

If it is normal ?

will this wear out he fuel gauge mecanism after a while,,??

any maintenance with light oil to the dash fuel gauge or something like that.

or is it a problem with the fuel sender?? 

or finally '' live it alone '' lol

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1 hour ago, lepic56 said:

any maintenance with light oil to the dash fuel gauge or something like that.

or is it a problem with the fuel sender?? 

or finally '' live it alone '' lol

Dash fuel gauge doesn't really have any need for oil or have parts that would wear out from the extra swinging. Oil would actually cause issues I believe. There is set of points that you clean on some gauges if they are not working but yours is working so leave it alone would be my recommendation. Most issues are with the sender but yours is working as it should and swings with the sloshing of the fuel some. 

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1 hour ago, jgreg53 said:

What is the round thing wired into the dash unit? And how do you test it?

I'm not sure if this question is directed to me for something I posted or someone else but please provide a bit more detail so we can help.  

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