Fuel gauge
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Tuned
Joined: Oct 2016
Posts: 255
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From: South dakota
Fuel gauge
i have a 1973 F-250 and when I fill the gas tank FULL the gauge only reads 3/4 or so. So this eve I unhooked the wire from the sender turned the key on and grounded that wire and the gauge goes all the way up. so my question is am I correct in thinking the sending unit is bad or is there something else to look for before i condemn the sender? because it looks like a process involved to remove the gas tank to get to sender. And hopefully the bolts are not rusted
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Sounds like a bad sending unit.
Test and tank drop 101. https://www.ford-trucks.com/forums/1...l#post14696841
Test and tank drop 101. https://www.ford-trucks.com/forums/1...l#post14696841
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Tuned
Joined: Oct 2016
Posts: 255
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From: South dakota
73 F 250 Fuel Gauge
OK I replaced The fuel float and it is slightly better went and fueled up Full as I could get it and It reads Just off Full Why would This do this when I ground the wire to Fuel Gauge and It will Peg out?? Don't understand wuts go-in on?
Laughing Gas
Joined: Nov 2013
Posts: 1,207
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From: S.E. Louisiana;so far USA
The gauge is still "seeing" some resistance from the sender. You can check it with an ohm meter. In order to get the gauge to read higher you'll probably have to bend the float arm some. When the tank is empty the gauge should read empty. Invert the empty tank and let the float rest on the top of the tank. The gauge should read full. Bend the float arm to get the best compromise for both extremes.
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Tuned
Joined: Oct 2016
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From: South dakota
Fact is I tested the new sender before I installed it and I held the float all the way up like the tank was full and the gauge still would be about a needle width away frtom full mark
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Laughing Gas
Joined: Nov 2013
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From: S.E. Louisiana;so far USA
I am assuming that when the sender is in the totally up position there remains some resistance in the circuit as compared to essentially zero ohm when the wire is grounded. The gauge is responding to the amount of resistance it "sees" in the circuit.
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Tuned
Joined: Oct 2016
Posts: 255
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From: South dakota
Fuel Gauge
Well turns out the circuit board on the back of my instrument cluster was bad along with IVR I replaced those 2 Items and all gauges functioned normal. I was also having inaccurate readings with oil Temp Gauges. But what I did seemed to be the cure. Musta been some kinda resistance in the old circuit board or IVR?
Thank you for you input!
Thank you for you input!
Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
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From: NE Texas
The arc that the float goes through is not necessarily exactly an evenly split arc... the angle that the pickup tub is bent at also affects this. In a perfect world the float would rest exactly at the center of its arc when there is exactly half a tank in the tank and ideally it will hit E when there is no gas in the tank and F when you top it off. In the real world if you get a repeatable reading at a given gas level so that you know when the gauge reads HERE you have about X gallons in the tank... be happy
Logistics Pro
Joined: Jul 2005
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Also don't forget to account for any taper to the sides of the tank. If the tank is wide in the middle, your gauge needle will go down slower because the wider area requires more fuel consumption to drop the level say a half an inch there.
Once the level reaches the taper, and the area gets narrower, the gauge needle will drop more quickly, and consume less fuel to drop the level another half of an inch.
Once the level reaches the taper, and the area gets narrower, the gauge needle will drop more quickly, and consume less fuel to drop the level another half of an inch.
Elder User
Joined: Jun 2005
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^Everything above rings true, but one other thing - resistance is finicky with weak connections, it could possibly still be a touch of corrosion somewhere that will cause some strange reactions at the needle. Yes, a dead ground will peg it with a possibly "weak" connection, but the resistance change isn't necessarily linear (as you found changing the board and IVR). You could sub in a jumper wire from the gauge to the sender and test it out, then start cleaning connections at the plugs.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Me I don't care if it reads full or not when full.
I do care when it reads Empty that I still have maybe 2 gal left in there.
Nothing like it reading 1/4 tank and run out of fuel. Been there done that and not any fun!
Dave ----
I do care when it reads Empty that I still have maybe 2 gal left in there.
Nothing like it reading 1/4 tank and run out of fuel. Been there done that and not any fun!
Dave ----
Laughing Gas
Joined: Nov 2013
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From: S.E. Louisiana;so far USA
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