How Do Fuel Sending Units Work ? BECAUSE
Fleet Mechanic
Joined: Feb 2007
Posts: 1,716
Likes: 0
From: Boston, MA
I will get it started for you. Did the problem just start out of the blue? I read that some gas is messing things up. I think it might have been shell. add some techron to the tank and switch brands if you use the same all the time. I did a search and found this site it is very interesting. basically the unit works on resistance. a full tank is zero resistance and an empty tank is infinity.
Fuel Tank Sending Unit Tech - FORDification.com
* i understand this is for older trucks but i believe the principle is the same
Fuel Tank Sending Unit Tech - FORDification.com
* i understand this is for older trucks but i believe the principle is the same
Last edited by powersmoked; May 15, 2010 at 07:08 AM. Reason: *
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It's not zero/open-circuit, it's 10 and 70 ohms for full and empty, respectively. This is for older trucks. I believe that at some point the direction reversed, such that low resistance is empty and high resistance is full. I'm not sure of the year or the values, but someone in the electrical forum would know. You are right on the principle though - the sending unit is a potentiometer.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,716
Likes: 0
From: Boston, MA
Ok thanks for clearing that up. I hadn,t my coffee yet 
. I will remmeber that, empty is empty "of ohms" and full is full of "ohms". I have read in a few places that some gas is effecting the SU and that in Theory Techron can solve it. You might as well run some techron in a few tanks. It is great for the truck anyways I believe Texaco and Chevron have techron in their gas
. I will remmeber that, empty is empty "of ohms" and full is full of "ohms". I have read in a few places that some gas is effecting the SU and that in Theory Techron can solve it. You might as well run some techron in a few tanks. It is great for the truck anyways I believe Texaco and Chevron have techron in their gas
Thread Starter
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Senior User
Joined: Feb 2004
Posts: 144
Likes: 0
From: Kansas
Thanks, I will take a reading today. and when the tank is lower ( NOW USING TRIP METER, TO KNOW WHEN TO FILL UP ) Then I will take a reading when I fill up. That should tell me if the sending unit is doing any thing at all. I might not have to drop the tank this way. Thanks again.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,716
Likes: 0
From: Boston, MA
Thanks, I will take a reading today. and when the tank is lower ( NOW USING TRIP METER, TO KNOW WHEN TO FILL UP ) Then I will take a reading when I fill up. That should tell me if the sending unit is doing any thing at all. I might not have to drop the tank this way. Thanks again.
you might want to post on the diesel thread here also?
Cranky Old Guy
Joined: Mar 2008
Posts: 3,562
Likes: 6
From: Raphine, Virginia
Ok thanks for clearing that up. I hadn,t my coffee yet . I will remmeber that, empty is empty "of ohms" and full is full of "ohms". I have read in a few places that some gas is effecting the SU and that in Theory Techron can solve it. You might as well run some techron in a few tanks. It is great for the truck anyways I believe Texaco and Chevron have techron in their gas
. I will remmeber that, empty is empty "of ohms" and full is full of "ohms". I have read in a few places that some gas is effecting the SU and that in Theory Techron can solve it. You might as well run some techron in a few tanks. It is great for the truck anyways I believe Texaco and Chevron have techron in their gasEdit: Excellent way to check gauges for proper operation.
