LB7 Fuel Level Sensor Scaling

[LBZ]

If I were to adjust the scaling in my fuel level sensor table, does anyone know if that will move the gauge accordingly?
When my cluster got new steppers and lights the needle got put on a bit high and I found this summer that it runs out of fuel at 1/8th of a tank now. So I was wondering if this would adjust the needle to read accurately again.

 

[2004LB7]

It will not. The stepper or more accurately the driver doesn't "know" where the needle is. It knows the exact location of the motor shaft. If the needle is off then it will always remain off until adjusted. Pretty easy to pop them off with a kitchen fork. The trick is to put it back on right. Had to deal with this on my truck before. Took several tries before I was happy with it. Got pretty fast at removing the gauge and opening it up. Easy enough for the RPM and MPH since they will hold at zero with the engine off and ignition on. But fuel level and the others won't

 

[DAVe3283]

If you have a Tech 2, you can command all the needles to 0 or 100% of scale, makes aligning them pretty easy. Just install it in the truck with the face off.

The low fuel light should come on regardless of the needle being wrong, so if that didn't happen, you might have another issue. I had my fuel pickup hose crack and below 1/4 tank it would suck air and die. Had to drop the tank and put a new hose in, then all was well again.

 

[LBZ]

So I’ve been playing with this and adjusting the scaling does indeed move where the needle is depending on tank level. Still working on the fine tuning but I’ll report back once I get it dialed.

 

[2004LB7]

Just remember, unless you fix the needle position the zero will never be zero

 

[LBZ]

Just remember, unless you fix the needle position the zero will never be zero

We’ll see. 0 was below the empty line before. Problem was 1/8th tank to zero was about a gallon instead of the 3 or so it should have been. So rescaling should shift it over enough.

There are about 30 or so points on the empty side that read zero but still reference a voltage and about 90 on the full side that read 100 but range from~2.5 - 5 volts so they allowed room to move it over some as needed.

I have it dialed fairly close to accurate from 1/2 tank to full based on where the needle was and the volume I put in when filling. Now I need to fill a fuel jug up and drive around till it runs out to see how close I am on the empty side.

Below are some snips of the stock table vs what it looks like after I adjusted. Before the needle would not move for 100 miles and then it would drop to 3/4 tank in about 10 miles. This was how the stock table appeared to be set - jumped from 66.27-100 in .02 Volts. By extending the ramp up and moving the 100 value over it smoothed out the drop and moved the needle back to the full instead of 3 needles over full. I'm hoping there's enough room on the empty side to do the same if needed.

You are correct though, if the voltage isn't enough or bounces around too much to be reliable on the empty side I will have to pull the needle off and move it.

 

[2004LB7]

I had the same problem when rescaling mine. The bottom end didn't have the resolution needed to completely fix the issue.

I'll see if I can find the values I used

 

[2004LB7]

This is from my LB7 in 2013 and a little discussion about my 08

re-calibrating the fuel level sensor {F0101}

for anyone wanting to re-calibrate the fuel level sensor on the 26 gal tanks these are the numbers that that i came up with: Gallons Voltage 0 gal 0.686275 1 gal 0.764706 2 gal 0.901961 3 gal 1.019608 4 gal 1.137255 5 gal 1.254902...

forum.efilive.com

 

[LBZ]

I vaguely remember that discussion. Thanks.
I'll report back in a couple weeks once I run out of fuel and let y'all know how I made out.

 

[LBZ]

I got it dialed in now. Light came on at 50km to empty and I ran it out for 45km and put 99 liters in so that’s close enough for me.

The mpg part is out to lunch though so that’s the next battle. I tried the calculator thing someone else posted and it went from being out 2l/100km to 5 so it went backwards for some reason.