Bad gas gauge?

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Dartalltheway

Dartalltheway

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My 1974 Dart Swinger gas gauge has always been giving me problems. First of all when it says empty it will fill up with 9 gallons and then say three fourths of a tank. Also I just put three gallons and it went from a little below empty to empty. I don't know what's going on and it's kinda frustrating. Any help much appreciated.
 
Ok I'll do all of that and see what happens. But while were on the subject of gas. Does anybody know why there is an air stem on the gas tank?
 
"Air stem?" What and were is this?

You talking about the 1/4 line going up front? That hooks into the "carbon can" and IS the vent for the tank
 
No I mean actual air stem.
 

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I believe I have air shocks, but then does that mean this only appears to be connected to my gas tank?
 
Yes it appears to be attached to the tank but is not.

Because it is not factory but the wire next to it is and it goes to the sending unit.

To cover the end of it so it dont get dirty it is the same size as the valve stem caps on your wheels.
 
That is an air shock fitting. You are not looking at your gas tank, you are looking at the floor of your trunk.
 
Fill it up. pierce the casing on that blue wire ( shove shirt pin through it will work ) and check it with an ohm meter. You're looking for 10 ohms +/- .5. If you see 16 to 18 ohms the gauge is correct at 3/4 tank and the float on the sender has some fuel inside it.
Drive the gas out of it while waiting for a new sender to arrive.
If you do see 10 ohms the sender is correct and the gauge is likely the fault.
Pull the instrument panel and check the same blue wire for the same 10 ohms there. Correct 10 ohms there confirms the gauge is wrong.
If you dont get the same reading there you have a wire connection fault probably behind the left kick panel.
 
Do not try to measure the OHMS with the ignition turned on. You will damage your ohm meter .
 
trapster said:
Do not try to measure the OHMS with the ignition turned on. You will damage your ohm meter .
Click to expand...

You don't measure the "OHMS", you measure the resistance of the device which happens to be in ohms. Much like current is measured in amperes or amps.
 
cudajim said:
You don't measure the "OHMS", you measure the resistance of the device which happens to be in ohms. Much like current is measured in amperes or amps.
Click to expand...

Maybe, but the meter doesn't say "resistance" usually, and these terms can be confusing, especially for guys who are "barely electric"

One time I was talking about "I squared R losses"

Someone said, "you mean heat?"

"Yes."

"Isn't that power?"

"Yes"

The same as watts?

"Yes"

"But isn't watts volts times amps?"

"Yes, in a resistive circuit, but here we are talking about the resistance of the wire, so it's I squared R, not volts times amps"

So then I had to explain THAT
 
Well the resistance according to my multimeter was 1. I put it at 200ma and it came out with 1.
 
Dartalltheway said:
Well the resistance according to my multimeter was 1. I put it at 200ma and it came out with 1.
Click to expand...


Lets try that again. Put the leads of the Ohms meter together. The meter should first zero and then show whatever restance is in its leads. Different scales moves the decimal point so... for example you would see .X or .0X or .00X
Check the senders resistance at the .x
1.0 ohms would fry the gauge.
 
Red, I'm sure you know better than I. Can you actually measure the sender without unhooking the gauge?

Maybe the wire IS shorted, or the gauge already bad.

I always go underneath, unhook the sender wire, OR get into the kick panel, and access the rear harness connector.

Your sender wire in the kick panel connector is the dark blue, at one end of the connector. Here we are measuring mine, at about 24 ohms which should read --and indeed does --read 1/2 tank on the gauge. One wire of the meter is hooked to ground, the other meter lead is hooked to the dark blue in the rear harness connector
 

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are you measuring amps or ohms ? you keep saying ma or milli amps but saying resistance which is ohms.
are you measuring between the blue wire and ground ? ohms or volts
are you measuring in series ? amps.

and please don't lecture me on ohms law, I am not the one that is confused.
 
trapster said:
are you measuring amps or ohms ? you keep saying ma or milli amps but saying resistance which is ohms.
are you measuring between the blue wire and ground ? ohms or volts
are you measuring in series ? amps.

and please don't lecture me on ohms law, I am not the one that is confused.
Click to expand...

Good point. The meter must be set to resistance, ohms.

What model is your meter, or post a photo of it?
 
So like this one? And you had the switch 180 from off, pointing to 200 ohms?

dmm2-1.jpg
 
67Dart273 said:
Red, I'm sure you know better than I. Can you actually measure the sender without unhooking the gauge?

Maybe the wire IS shorted, or the gauge already bad.

I always go underneath, unhook the sender wire, OR get into the kick panel, and access the rear harness connector.
Click to expand...

Yeah , not everyone has a floor jack and proper stands. I do have these things but I've had this "don't work hard, work smart" mindset for a very long time.
I would rather go under the car only once, new sender in hand.
To answer your question,
There may be a ground path through mechanical limiter that would change the results. I guess I'm spoiled by the solid state regulater too. Sorry.
Seperating the harness connecter behind the kick panel is a better method.
 
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