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Discussion Starter #1
I just installed my 75 gallon aftermarket tank in the bed of my 06 4dr,4wd,dually lariat PSD. It is a gravity flow tank that is connected to the fillneck. Fuel flows into the factory tank as the truck burns it. My guage stays full for 800 miles, then, when the guage drops off of full, i know that my aux tank is empty, and i now have the rest of the original facory tank to run on for another 350 miles.

I have had this same tank in my last two trucks, both ford diesels, one was a 1996, and the other was a 2000 year model.

The problem is this truck has a sensor that keeps making the check engine light come on. The mechanic at ford said that the dtc that comes up is due to an overfilled tank, and that fuel needs to be added to the truck only while the key is off. I guess you cannot leave the truck running while filling up.

I want to konw if anyone knows how to disable this sensor without tripping the light. The sensor is located on the top of the tank.
The light does not bother me, i just don't want to miss a warning that something else is wrong with the truck while the light stays on all of the time due to the overfilled tank.

Any input is appreciated.
 

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I have been researching this myself as I want to add an aux tank, but read where this would occur with a gravity fed tank.

I'm not sure about the sensor being tripped by the tank being over full. I haven't seen that being the cause anywhere else.

From everything I read, others are saying the code is tripped because the fuel level doesn't change over a period of time (remains on full).

Either way, I have found 3 options that I'm currently considering:

1. Transfer Flow, they have a pump/controller that keeps the fuel balanced between the tanks, so as you use out of the main tank, it transfers some back into it from the aux so they remain balanced.

2. Zylstra, they have an automated fuel controller that monitors the main tank. When it gets down to 1/4 full, it transfers fuel until the main tank is up to 3/4, then shuts off.

3. Homemade modification to the gravity flow system. I was thinking that a electric valve could be added so fuel only transfers when activated. I was then thinking of a circuit that could open the valve when the ignition was turned off and stay open for x number of minutes. Possibly a manual control to it as well.

Since I hadn't heard of the "overfull" sensor before, option 3 might not be so good since it would still fill it up to the top each time it was shut off.
 

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I watched the mechanic perform the diagnostic test. He said that there is a TSB technical service bulliten on that particular sensor. I read the TSB myself, and it said that the sensor tripping is caused by aftermarket gravity tank systems, or aftermarket remote start system.

It said that fuel should only be transferred into the tank with the key in the off position.

I also looked into transfer flow tanks, but they were very pricey. I had my tank built out of aluminimum diamond plate for 400.00. The tank sits flush with the bed, is not visible from the side unless you are right by the truck. The top 8 inches of the tank is a toolbox, and the rest of the bottom of the tank holds the fuel. I had it baffeled twice from front to back of truck, and three times from right to left of the truck. I have a cut off valve on the bottom of the tank with a in line filter.

It really works great, i hope I can figure out how to disable the sensor.
 

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I don't know how you would disable the sensor, hopefully someone else has some ideas.

I wonder though, if you shutoff the valve on your aux tank before you started the truck each time, and then opened it each time after your turned it off, if the sensor would be happy sense it would only be transferring fuel when it was off...kind of like topping it off after each running.

Now, I'm not suggesting that as a solution, more of a test. I was thinking of a way to do that automatically since it would be rare for me to drive non-stop thru a full main tank of fuel.

I'm wondering if the sensor would still complain because the main tank was filled to the top each time it was started.
 

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http://dan.prxy.org/Truck/6L_bible_html/html/Page_028.html

Maybe this can help; this link is to a 6.0L fuel flow and component chart that come with an operational description.
Most likely the sensor is either normally open or closed which should make it easy to bypass, but I am not a diesel tech. I am new to diesels and just learning myself. Reading the descriptions I would think by passing the sensor may not be a good option if it is tied to any other function described on the provided link.

Good luck, when you find the answer please let us know
 

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That is the valve system I have on a RDS tank. Use will not eliminate the check engine light problem.....I suspect that the gravity flow system is in fact the cause of the check engine light problem. Fuel will fill to the top of the fill neck. The fuel gauge continues to work, but with the light on, no other warnings get through. You can clear the light when the aux tank is empty with an ODB with a reset or disconnect the batteries for a few minutes. My aux tank is larger than the in truck tank so "over flows" will continue. I run the lower tank down to 1/4 before I switch to the aux tank. When running at 12 MPG it take takes a long time to fill. Next rest rest stop I shut off again. And so on. My bladder insures that I stop often enough. In California the check engine light will cause a smog test failure. Clear the code and run w/o the aux tank for 3 days.
 
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