Fuel gauge

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brianzie

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The subject of fuel and temp gauges not working has been covered a lot but I couldn’t find my specific conditions

My 1967 Barracuda fuel gauge doesn’t work. Temperature gauge does
Finding 12 volts at the fuel tank sending unit -even with key off.
I could understand if both gauges didn’t work and the built in voltage reducer was shot. But one works one doesn’t and key off voltage???
Looking for suggestions
 

Is the ground strap attached from the tank sending unit fuel line to the car fuel line?
 
The ground strap is a common issue. Otherwise, it is conceivable that the gauge part of the fuel gauge has failed while the VR part still works.

When you say it doesn't work, does it read F or E or what?
 
I would start by separating the rear harness at the left kick panel connector. See if the sender wire is shorted in the harness to any other wire(s) in that rear harness



Have you recently had any shorts, hot plastic smell or smoke?
 
The fuel sender is a ground, no power there. The element inside provides a resistance to ground. Grounding the sender wire will cause the gauge to read full if all else is good.
 
A regulator that doesn't have a ground doesn't regulate. Supplied volts paases right through. Now let's imagine someone added a solid state regulator and tapped the smp gauge for power. OK, maybe your imagination don't go there. How about wires moved about at the main inst' panel connector? There was a guy who had all those wires in wrong places. He was using the factory serve manual but he didn't notice that the connector was drawn on paper rotated 90 degrees. He admitted his beer goggles. My final responce to him, "its 5 o'clock somewhere." Good luck
 
Murray said:
The fuel sender is a ground, no power there
Click to expand...
That is correct TO the sender, but from the gauge you will see fluctuating voltage from the IVR and on a DVM it will be numbers all over the place.

 
Just recalled that a yellow wire in the rear harness is hot at all times. If it was shorted to the blue sender wire and that wire went to ground fuse blows. Are we having fun yet?
 
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The most common problem is the tank ground.
Fuel Tank Sending Unit Ground Strap - Steel - Fits many Dodge Plymouth models

1756987506308.png
 
Thanks for the inputs
67Dart got me thinking about some strange wiring connections in the trunk.
Pulled the wiring diagrams and discovered someone had cut off the connection for the C pillar lights on my fastback and connected the yellow to yellow -ok but then the pink wires (lights) and dark blue (sender) wires together -oops. That’s where the 12 volts came from.
Corrected the connections. Now lights work but I see no voltage with key on at the sender (blue wire). I have the ground strap -not sure it’s on right so I a wire from the sender to ground. Still no voltage or reading in the gauge (reads empty)
 
We have to get something like 5 volts to and though the fuel gauge. With original voltage limiter working a digital meter will show random 2.X, 3.X, to average 5VDC. that's what we need to see at the sender. A solid state regulator would show steady 4.X but i doubt that has been installed. If 12 volts fed backwards, I have no clue of consequences.
 
I would highly suggest checking the wiring to C pillar/cargo lights. I redid all my wiring there. Scary how close to metal the bulb holders are to grounding out.
 
brianzie said:
cut off the connection for the C pillar lights on my fastback and connected the yellow to yellow -ok
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FYI

The c pillar lights get power on one wire and then goes to ground through door switches and or the headlight switch turning it CCW to the click.

If that had happened the yellow would have had a direct short to ground
 
If power though a bulb filament to ground is considered a "direct short to ground",,, call the fire department.
 
RedFish said:
If power though a bulb element to ground is considered a "direct short to ground",,, call the fire department
Click to expand...
Maybe I misunderstood your description.

I thought you said that someone cut off the connections for the c pillar lights and tied them together, my interpretation was they removed the c pillar lights and connected the wires that feed the light bulbs together
 
Dana67Dart said:
Maybe I misunderstood your description.

I thought you said that someone cut off the connections for the c pillar lights and tied them together, my interpretation was they removed the c pillar lights and connected the wires that feed the light bulbs together
Click to expand...

My comment before was inappropriate regardless. Probogation of erroneous information bugs me bad. The damned adds here don't help. I'll be at the liquor store when they open. Have a nice day
 
RedFish said:
My comment before was inappropriate regardless. Probogation of erroneous information bugs me bad. The damned adds here don't help. I'll be at the liquor store when they open. Have a nice day
Click to expand...
It's all good.

To @brianzie

Photos help a bunch.

I see your new to FABO, welcome aboard the crazy train!


Some times in our zeel to help we let our mouths run faster then our brains so don't get discouraged.

Did you watch the video on how our thermostat electric gauges work?

Also the description of what wires were tied together needs some clarification.

I'm not sure which wires were tied to which.

The ralley clusters have the IVR internally in the fuel gauge. If the IVR is functional but the gauge is toast that would have the effect of slowing the temp and oil pressure gauges to function but not the fuel.

When testing the gauges start by (key off) shorting the sender wire AT the sender (sender wire removed from its respective sending unit.)

Then turn the key to run, the gauge in question should rapidly move to Full, high, 60 etc. as it's rising turn the key off or you WILL burn out your gauge.

Restore the sender wire

Do this on each gauge. And report back
 
Clarification
Hopefully the attached helps

Testing temp and oil pressure both went quickly to max -high/ hot after one second delay

image.jpg
 
Well, to me, the bottom line is that you need about 5V from the IVR going through the gas gauge to the gas tank sending unit. Then the rheostat in the sending unit will allow a certain amount of current to flow through to ground. The more current that is allowed to flow to ground (determined by the float), the more current will be flowing through the bi-metal coil in the gas gauge, and more current passing through that coil will cause it to heat up more and move the needle more. If the gas gauge itself is bad (not letting any current through at all) then the needle will not move. The IVR must be OK or the temp gauge would not work. Does the oil pressure gauge work? If there is 5V at the gas sending unit (and it will be pulsing), then start looking at a ground problem or a bad sending unit.
I hear what you are saying about your C pillar lights. Get that problem sorted out and then figure out if you have 5V going to the sending unit.
 
brianzie said:
Testing temp and oil pressure both went quickly to max -high/ hot after one second delay
Click to expand...
I'm assuming that you tested both by key off shorting the sender wire to ground them turning the key to run for a couple of seconds on each sender wire individually.

If that is the case then that is good and suggests the IVR is functioning as it should.

If you did the same with the fuel gauge sending wire and nothing happened then you have to trace the wire back from the fuel tank and do the same test at each junction along its route.


Dana67Dart said:
Did you watch the video on how our thermostat electric gauges work
Click to expand...
I did not see an answer on this question.


Your diagrams did not make a lot of sense to me.

The basic sender gauge configuration is as follows.

  1. Battery (12v) to terminal on cluster
  2. Terminal on cluster to a pin on the fuel gauge (IVR input)
  3. Inside the fuel gauge the IVR works like a blinker mechanism (open contact and nothing of the 12v flows to the gauge, closed contact and all of the 12v flows to the gauge. The open close cycle is such that the average is about 1/2 of the time the contact is open so the average voltage seen by the gauge is 1/2 of 12v or about 5-6 volts
  4. This 5-6v goes directly to the fuel gauge and out a pin to the temp and oil gauge IVR input pins
  5. Inside any of the three gauges the input from the IVR goes to the heater wire wrapped around the bimetal part that the needle is attached to. The other end of the heater wire goes to the sender
  6. In the sender the wire goes through a variable resister and and then to ground
  7. depending on pressure or temp or position the resistance increases or decreases.
  8. More resistance and the heater wire in the gauge gets cooler, needle to L, E or 0. Less and the heater wire in the gauge gets warmer and the needle goes to H, F, or 60
 
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Regarding the testing of the gauge functions, I thought I indicated that I tested both the Oil and Temp gauges as suggested in an earlier posting - both function OK
Also with my corrected wiring the C pillar lights work as they should.
I have no voltage at the fuel sending unit. no breaks in the wire from dash to sending unit. Sending unit tests at 22 ohms (tank nearly full)
Grounded sending unit wire - turned on ignition - no fuel gauge response.

Regarding the diagrams - I hoped they'd be self explanatory - I guess they weren't - my bad
The diagram shows the wiring as it should be (my poor copying of the Shop Manual diagram). the second section is the way I found it with the three prong connector cut off and the wires incorrectly patched together. the third section depicts my direct ( and separate wiring) of the yellow, pink, and blue wires (blue being the one that goes to the fuel sending unit.

Bottom line - everything seems to be functioning correctly (Temp/Oil gauges and C Pillar lights)
The issue seems to be I don't see any voltage at the fuel sending unit (blue wire) and therefore I'm suspicious that the previous wiring snafu caused 12v to the sending wire and that probably toasted the gauge ( but not the IVR - since the other gauges work)
 
brianzie said:
Regarding the diagrams - I hoped they'd be self explanatory - I guess they weren't - my bad
The diagram shows the wiring as it should be (my poor copying of the Shop Manual diagram). the second section is the way I found it with the three prong connector cut off and the wires incorrectly patched together. the third section depicts my direct ( and separate wiring) of the yellow, pink, and blue wires (blue being the one that goes to the fuel sending unit.
Click to expand...
I think part of the problem ,at least for me, is I don't know the wire color and what it goes to.

Marking it "blue (from sender)" or "blue (to sender)" would help at least me.


brianzie said:
Sending unit tests at 22 ohms (tank nearly full)
Click to expand...
Sending unit with a nearly full tank should read closer to 10 ohms, 22 is almost 1/2 tank reading.
 
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