More gremlins...
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Elder User
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More gremlins...
My gas guage recently dropped to empty and stayed there. First thing I thought was a leak... not so. Out comes the test light. When I jump between the end of the ground wire and the post it goes to on the sending unit, nothing. When I jump between where the ground wire goes to the body and the pos terminal on the sending unit (wires still connected), the light flashes and the guage goes up to where I thought it should be... 
??
-Andrew
f250_64(No Email Addresses In Posts!), same for yahoo messenger
Nothing, and I mean nothing, stirs the soul, saying I'm a bad **** like lettin'em rip with a window shaking, fuel gulpin, carbon monoxide belchin, attention gettin, V-oh my LORD!-8!
??-Andrew
f250_64(No Email Addresses In Posts!), same for yahoo messenger
Nothing, and I mean nothing, stirs the soul, saying I'm a bad **** like lettin'em rip with a window shaking, fuel gulpin, carbon monoxide belchin, attention gettin, V-oh my LORD!-8!
Moderator
Joined: Jan 2001
Posts: 56,999
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From: Virginia
More gremlins...
The test light is kind of confusing when trying to test this
circuit. The wire that is not ground, that comes from the guage,
should be pulled off the sending unit and left hanging in the air. With the key on the guage should read all the way to one
side(I can't remember if it should be empty or full). Then if
you take a jumper wire and ground this wire from the guage(to a
known good ground), the guage should go all the way to the other side. If this works, you know the guage and wire are ok. Then I would take the jumper wire and try grounding the guage wire at the sending unit ground. If the guage still works you know your
gas tank has a good ground. If all this checks it has to be the
sending unit. I usually try to fix these myself. Usually the
brass wiper inside is broke off, or getting ready to break off
and is not touching the windings. You can carefully bend back
the tabs that hold the cover on and see what I am talking about
after you get it out of the tank. I just solder the wiper back
on and and put it back together.
circuit. The wire that is not ground, that comes from the guage,
should be pulled off the sending unit and left hanging in the air. With the key on the guage should read all the way to one
side(I can't remember if it should be empty or full). Then if
you take a jumper wire and ground this wire from the guage(to a
known good ground), the guage should go all the way to the other side. If this works, you know the guage and wire are ok. Then I would take the jumper wire and try grounding the guage wire at the sending unit ground. If the guage still works you know your
gas tank has a good ground. If all this checks it has to be the
sending unit. I usually try to fix these myself. Usually the
brass wiper inside is broke off, or getting ready to break off
and is not touching the windings. You can carefully bend back
the tabs that hold the cover on and see what I am talking about
after you get it out of the tank. I just solder the wiper back
on and and put it back together.
Thread Starter
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Elder User
Joined: Jul 2000
Posts: 571
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More gremlins...
I don't think it's the float, because the guage dropped instantly all the way down.
Franklin:I do not understand one thing you said...
There's 2 wires, one that goes to the guage, and one that goes to ground. When I unplug the ground wire from the unit, and jump between it's connector and it's post, nothing. When I jump between the wires, the light flashes and the guage works...???
-Andrew
f250_64(No Email Addresses In Posts!), same for yahoo messenger
Nothing, and I mean nothing, stirs the soul, saying I'm a bad **** like lettin'em rip with a window shaking, fuel gulpin, carbon monoxide belchin, attention gettin, V-oh my LORD!-8!
Franklin:I do not understand one thing you said...
There's 2 wires, one that goes to the guage, and one that goes to ground. When I unplug the ground wire from the unit, and jump between it's connector and it's post, nothing. When I jump between the wires, the light flashes and the guage works...???
-Andrew
f250_64(No Email Addresses In Posts!), same for yahoo messenger
Nothing, and I mean nothing, stirs the soul, saying I'm a bad **** like lettin'em rip with a window shaking, fuel gulpin, carbon monoxide belchin, attention gettin, V-oh my LORD!-8!
Posting Guru
Joined: Aug 1999
Posts: 1,485
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Andrew, remove the entire sending unit from your tank. Inspect the float for a "flooding" situation. If the float is OK, hook up the wires to the sending unit and move the float up and down while watching the gauge. If still nothing, visually inspect the sending unit, ground, wire connections, etc. and report back your findings.
Nathan
Nathan
Moderator
Joined: Jan 2001
Posts: 56,999
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From: Virginia
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Basically, one side of the guage is fed with a constant + voltage
from the guage regulator. The other side of the guage is the wire that goes to the sending unit in the tank. The sending
unit's job is to more or less ground this wire, completing the
circuit. The sending unit is a variable resistor. It's value
depends on where the float is positioned. It will have a very
low value on one extreme, and a very high value on the other.
Taking the guage wire off and letting it hang, represents a very
high resistance to ground. Grounding this guage wire represents a very low resistance to ground. This should move the pointer
of the guage to it's extreme positions, telling you if the guage is working. If you jumped the connector, shorting the guage wire to a good ground, and the guage moved, I would say the
guage is working. If you jumped the guage wire to the ground post on the unit, and the guage didn't move, that post is not
a good ground probably. Thats why the ground wire is included
in the harness.
from the guage regulator. The other side of the guage is the wire that goes to the sending unit in the tank. The sending
unit's job is to more or less ground this wire, completing the
circuit. The sending unit is a variable resistor. It's value
depends on where the float is positioned. It will have a very
low value on one extreme, and a very high value on the other.
Taking the guage wire off and letting it hang, represents a very
high resistance to ground. Grounding this guage wire represents a very low resistance to ground. This should move the pointer
of the guage to it's extreme positions, telling you if the guage is working. If you jumped the connector, shorting the guage wire to a good ground, and the guage moved, I would say the
guage is working. If you jumped the guage wire to the ground post on the unit, and the guage didn't move, that post is not
a good ground probably. Thats why the ground wire is included
in the harness.
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