help, gas guage doesnt work
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Junior User
Joined: Jun 2003
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From: southern cal
help, gas guage doesnt work
I need help with my gas guage, the needle stays on empty when i start the truck, but when i disconnect the tank switch it goes all the way to full, can somebody give me procedures to check it or to try something, both tanks do the same thing , empty and full when disconnecting the switch.
New User
Joined: Jan 2008
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That means it is grounding out
These gauges work on a the grounding principle.
The more *ground out* the higher the reading.
They also run with a resistance factor.
I'll go find my diagram.
Things that cause the needle to stay on empty or close.
1) Float full of gasoline
2) Bad Sending unit
3) Bad resistance factor of sending unit.
4) Bad Cluster Voltage Regulator
What causes the gauge to go to Full
1) Direct *Ground out* from S/U or Circuit Wiring.
These gauges work on a the grounding principle.
The more *ground out* the higher the reading.
They also run with a resistance factor.
I'll go find my diagram.
Things that cause the needle to stay on empty or close.
1) Float full of gasoline
2) Bad Sending unit
3) Bad resistance factor of sending unit.
4) Bad Cluster Voltage Regulator
What causes the gauge to go to Full
1) Direct *Ground out* from S/U or Circuit Wiring.
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Junior User
Joined: Jun 2003
Posts: 73
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From: southern cal
i have already changed the cluster and it did the same thing , does this mean that somewere before the dual switch the wires are grounding? both tanks read the same.
EDIT:
it stays on empty when ignition is on and goes to full when tank selector is disconected
EDIT:
it stays on empty when ignition is on and goes to full when tank selector is disconected
New User
Joined: Jan 2008
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I understood right from the start.
This grounding out system is what is used to make the gauge needle go back and forth
Normally:
A full tank of fuel causes the grounding affect more so the S/U is reads at its peak.
When the fuel tank is near empty, the grounding affect the ground in less causing the needle to fall.
The outright Pegging of the needle is because the wire is grounded out without resistance.
This grounding out system is what is used to make the gauge needle go back and forth
Normally:
A full tank of fuel causes the grounding affect more so the S/U is reads at its peak.
When the fuel tank is near empty, the grounding affect the ground in less causing the needle to fall.
The outright Pegging of the needle is because the wire is grounded out without resistance.
Senior User
Joined: Aug 1999
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From: Bel Air USA
You don't say what year or model truck you have. At one time, back in the 70's the fuel gauge would read full with low resistance (10 ohms) and empty with high resistance (73 ohms). Somewhere in time Ford changed the way their gauges worked. I don't know which year it was. I do know that on a 93 F150 that low resistance (22.5 ohms) makes the gauge ready empty and high resistance (145 ohms) makes the gauge read full. This is the opposite of the earlier gauges. Assuming you have one of the later type I would say your sending units are both bad since unhooking them essentially makes the resistance go high (open circuit). This would be easy to check with an ohmmeter. Unplug the fuel sending unit and measure the resistance. If it is low (22.5 approximately) then your gauges are reading what is being sent to them correctly. This means your sending units are bad.
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From: southern cal
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From: Virginia
Very simple fuel guage and wiring check.
Take the wire off the sending unit at the tank, and ground it. The guage should swing full scale one way. Take the wire off ground and let it hang in the air. The guage will swing the other way full scale. This will tell you if your wiring and guage are working.
Take the wire off the sending unit at the tank, and ground it. The guage should swing full scale one way. Take the wire off ground and let it hang in the air. The guage will swing the other way full scale. This will tell you if your wiring and guage are working.
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Dave he already stated that the Gauge pins after he removes the wire from the connector on the S/U without touching anything.
Earlier That told me it was grounding out , Then I found out it is a newer truck which uses the opposite sytem from the old ones
Earlier That told me it was grounding out , Then I found out it is a newer truck which uses the opposite sytem from the old ones