Fuel Gauge

2008 FORD F-150
8,500 MILES • V8 • 4WD • AUTOMATIC
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KLMONE
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Hi,

I have what I think is an unusual question that I hope you can help with. I have currently a 2008 F150 FX4. I bought it with the standard 27 gal. fuel tank. My old truck was a 2005 F150 FX4. It had the 36 gal fuel tank option. I wanted the bigger tank on my new truck, so I looked at the dimensions and all I could figure to look at and the only difference I could see was that the 36 gal. was longer. I figured that the sending unit would work and things would be good. I wasn't able to "fill" the tank when the prices were at $4.00 a gal. and the gauge worked accurately but now that they have dropped I am able to fill the tank. When I fill it, the gauge goes to empty and the "low Fuel" warning comes on for about the first 60 miles. Now, the gauge "misreads" and I found this out on a recent trip to Vegas. I filled the truck before I left AZ and when I went to leave Vegas, the gauge read about half. I filled it and ended up putting 25 gals in.
So, now that the background is out of the way, is there a way to "adjust" something to make the gauge read right?

Thank you,
Ken Maki
Scottsdale, AZ
602-697-3461
Feb 25, 2009 at 11:01 AM
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JACOBANDNICKOLAS
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If the gauge is dropping to E when full, the float must be over extending past the rheostat limits and loosing connection. Unfortunately, it is only so long and can't be extended. Somewhere inside the tank, something must be different and allowing it to travel beyond it's limits.
Feb 25, 2009 at 8:53 PM
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KLMONE
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I think I need to clarify some more. When I did the tank swap, I left the sending units intact in each tank since all the connections were the same. The guages on both trucks worked fine before the swap. I was also carefull to not "Drop" the tanks. Could the sending unit have gone bad? And back to my original question, is there some "Adjustment" that can be made to correct this?
Feb 26, 2009 at 6:29 AM
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JACOBANDNICKOLAS
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There are no adjustments. Also, it sounds like the sending unit is bad.
Feb 26, 2009 at 7:17 AM
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KLMONE
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OK,
The sending unit has been replaced. I confirmed that this is the correct sending unit for this vehicle. There is no difference to the guage reading. Are you able to actually help with this or is this questoin beyond your capabilities?????
Mar 5, 2009 at 7:23 AM
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JACOBANDNICKOLAS
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Hi:
First I'm not there. And no, I assure you this isn't beyond my capabilities. My problem is we have a 2005 tank in a 2008 truck. I know everything looks the same but there could be something different in the tank that is causing the problem. 99% of the time when the gauge does what you described, the sending unit for the float is the problem. I will ask for the opinion of the other techs here to see if they have something different for you.
Mar 6, 2009 at 9:01 PM
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STRAILER
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hi klmone, sounds like you are having a dozy of problem. On the 08's all fuel level feedback info is processed through a fuel tank module (near the fuel tank) then on to the BCM and onto the gauge. As you can see the resistance is very important and I can tell you from experience ford likes to change stuff even if it seems like it should work, the resistance is different on the 06 sender. The new tank sender is the problem. Try swapping the senders and let me know what happened.
Mar 7, 2009 at 2:17 AM
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KLMONE
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That's what I did. I switched the old '05 sending unit to the correct '08 sending unit. And I have found out Ford does like to mix things up. They offer, according to the parts guy, different sending units for different truck body styles too, even if the tanks are the same. I am about ready to see if I can slip this one by them as a warranty issue just to see if they could figure it out. I think I will see if using the VIN to check for a different sending unit makes a difference, i don't know if they can look up parts by the VIN, but it sounds like a good idea...
Mar 7, 2009 at 7:53 AM
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STRAILER
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Yep, good call, I was thinking the tank modules go bad pretty easliy. It could be your problem. Please let me know what happens. Thanks for using 2carpros.com
Mar 7, 2009 at 12:49 PM
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AUSTIN ROY
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my truck that I recently bought had a broken fuel gauge which was stuck past full. when I was told that the fuel pump was going bad on it and the sending unit was bad in it I replaced it, but after I bought a new fuel pump for it, the gas gauge still is stuck past full.
Nov 14, 2019 at 12:28 PM (Merged)
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MHPAUTOS
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The gauge has probably been damaged, sometimes when they see a voltage spike or the such it sends the gauge past its working parameters and they will get stuck there.

See the diagram below for the wiring you need to check as well as the guide on how to use a voltmeter to test the gauge

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Let us know what you find
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Nov 14, 2019 at 12:28 PM (Merged)
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FLASHHEAT
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Thank you for this post I had this problem and had to replace the instrument cluster cost me $164.00 all fixed I love this site.
Nov 14, 2019 at 12:28 PM (Merged)
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ILOVEMYFORD2010
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I have a 2008 F150 and the low fuel light keeps coming on and off and my fuel gauge drops of then goes back to normal. ford told me to take the battery lug off for 20 minutes. i did that and its still the same. i have tried gasline antifreeze like they said and filled the tank with gas and its still the same. i just dont know what to do. please help
Nov 14, 2019 at 12:29 PM (Merged)
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BLACKOP555
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if i was you i would be checking for unusual resistance in the fuel level sending unit wiring harness and unit itself.
Nov 14, 2019 at 12:29 PM (Merged)