Bad Fuel "Gauge"? (1965 Barracuda)

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65cudaVR

Early A-Bodier
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I've been trying to troubleshoot an ongoing problem with my fuel gauge system. I think I have narrowed it down to the fuel gauge itself, but I was wondering if anyone else has experienced this particular problem...

Before I describe the situation I just wanted to say that I have already (more or less) ruled out other possible problem areas (I think):

I have a new SENDING UNIT (see below for test results)
I have a new "solid state" VOLTAGE LIMITER (from rt-eng.com - also see below for test results)
GROUND tested good.

Ok, so here's what it's doing:

When the SENDING UNIT is at the "empty" position, the gauge shows exactly empty, and when it's at "full" position the gauge shows exactly full. So far so good, right? BUT, when I have the SENDING UNIT set to approximately the middle, the fuel gauge shows a quarter or less and once it gets to about 1/3rd the way up it pretty much shows empty:

View attachment FuelSenderA.jpg

So, once it shows empty then I could have between 0 to 6 gallons in the tank, which kind of sucks trying to predict how far I can go when the gauge indicates that it's empty (I already had an instance where I ran out of gas because I wasn't sure how much was left in the tank).

As I mentioned earlier, I tested everything else. Here are the results:

A) SENDING UNIT - Using a multimeter I tested the resistance which was at about 80 ohms (empty) to about 9 ohms (full) and as I swept the float arm upwards the readings adjusted accordingly (went from 80 to 70 to 60, etc) as you would expect:

View attachment FuelSenderB.jpg

EDIT: See Post#12 below and the article I attached which describes a similar problem with fuel senders on early Ford vehicles!

B) VOLTAGE LIMITER - I also tested the DC Voltage with the multimeter on this device as well. The readings fluctuated from approximately zero volts to various high readings between 4 to 7 volts for example:

0-4 volts
0-7 volts
0-4 volts
0-6 volts
0-5 volts
0-7 volts... etc

My understanding is that this is normal since the RTE voltage limters are designed to mimic the original contact point Mopar limiters (to approximate a 5 volt power source).

C) I also made sure the SENDING UNIT had a good GROUND as well, so that shouldn't have be an issue either.

Anyway, my next step is to replace the gauge with the hopes that it will solve my problems, but before I undertake that project, I was wondering if anyone else has encountered a similar situation and whether there's something else I might be missing.

Thanks in advance!
 
Check the ohms reading at the wires at the gauge with it disconnected, if they are like the ones you posted it is a bad gauge for sure. I have been making test sets for the gauges lately and you readings are pretty much spot on 10 full, 23 mid, 73 empty is the resistance value for the three settings.
 
You probably have a worn out sending unit, corroded, poor contact, etc, etc

The thing is just incredibly simple. It is simple resistance wire, wound onto a form, with a moving contact. This is otherwise known as a "rheostat." The moving contact and or the wire can be corroded / rusty, and lose contact "suddenly." You could try a "gentle" cleaning method.

The whole darn problem is, that the "repop" replacements don't seem to be accurate.

Some more.......

http://www.forabodiesonly.com/mopar/showthread.php?t=341468&page=4

and in this thread

http://www.forabodiesonly.com/mopar/showthread.php?t=264543

you can buy this calibration unit

http://www.forabodiesonly.com/mopar/showpost.php?p=1970459870&postcount=96
 
What did you do about the original limiter ? If you did what RTE says to do ( bend the little thingy ) you had to open the gauge. If so, What did you see in there ?
As for the ohms readings at float positions you've presented, 23 ohms aint near the middle is it ? Instead it's just a click away from full. Linear versus non linear sender construction.
 
Get a 0-100 Rheostat from radio shack (or gut a volume control but thats less precise) and wire it up to your gauge. turn the dial and see if the sweep of the gauge can be duplicated using a VOM to check your resistance level per your readings. How a gauge can go bad is a question for Kit.
 
RedFish said:
What did you do about the original limiter ? If you did what RTE says to do ( bend the little thingy ) you had to open the gauge. If so, What did you see in there ?
Click to expand...

I'm not sure if we're talking about the same thing.

My Voltage Limiter is mounted on the printed circuit board of the instrument cluster. It's not directly connected to the fuel gauge in any way.

RedFish said:
As for the ohms readings at float positions you've presented, 23 ohms aint near the middle is it ? Instead it's just a click away from full. Linear versus non linear sender construction.
Click to expand...

I didn't do an accurate reading of the resistance, I was just pointing out that the Sending Unit had a smooth transition on readings from the empty to full positions.

My assumption is, if the gauge were working correctly, that at 80 ohms it would read empty and as I move the arm upwards (lowering resistance) the Fuel Gauge would adjust somewhat proportionally to the change, but there is no change until it reaches about 1/3 the way up, which doesn't make sense.


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65cudaVR said:
I'm not sure if we're talking about the same thing.

My Voltage Limiter is mounted on the printed circuit board of the instrument cluster. It's not directly connected to the fuel gauge in any way.



I didn't do an accurate reading of the resistance, I was just pointing out that the Sending Unit had a smooth transition on readings from the empty to full positions.

My assumption is, if the gauge were working correctly, that at 80 ohms it would read empty and as I move the arm upwards (lowering resistance) the Fuel Gauge would adjust somewhat proportionally to the change, but there is no change until it reaches about 1/3 the way up, which doesn't make sense.


`
Click to expand...

OK so maybe your 65 doesn't have a 3 post fuel gauge with original limiter inside. My memory doesn't work so well, especially while on pain meds.I had hoped you had seen what age has done to the inside of that gauge. A restored gauge would work a lot better but still wouldn't be perfect with the aftermarket sender.
The OEM gauge isn't designed for a linear sender. If it was, half tank would be half way between 80 and 10 which is what 35 ? or is it 45 ? see your info, the linear sender is 45 at half. :)
 
It might be that the gauge is mechanically sticking. "How old" again, are these girls?

crazy-old-women-8.jpg
 
67Dart273 said:
you can buy this calibration unit

http://www.forabodiesonly.com/mopar/showpost.php?p=1970459870&postcount=96
Click to expand...

Looks like a great product. I'm not sure if I like the fact that Fords and Mopars need a separate unit with a built-in regulator, since it requires further monkeying around (more to go wrong and with limited space under the dash).

I did find the article they linked to interesting (see PDF at bottom) ...especially this part:

View attachment MeterMatchDoc.JPG

This sounds very similar to my problem; at least the part about it going straight to empty "with as much as a quarter tank of gas" still in the tank.

Now I'm back to suspecting my sender again! :scratch:

Any suggestions on where to find the most compatible sender?

Anyway, here's the full article about the "Meter Match" review:

[ame]http://www.technoversions.com/MeterMatch-Fairlane.pdf[/ame]


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