Can fuel sending unit be calibrated?

[Brain75]

check the wiring (resistance to ground specifically) on the lead going to your sending unit... and wiggle the whole braid around a little while you are checking. I bet you have a bad ground. Intermittent stuff like that is a lot of times (usually) ground.

As far as your question, the non-ground leg ends up at the fuel gauge in the dash, the ground leg goes to ground on frame somewhere.

I forget which is which, but if it goes way past full or way below empty and sticks, you have a short or no ground. one is no resistance, the other is infinite resistance, and if you are familiar with the vehicle you will know what is past the end of the normal range easily.

 

[Brain75]

... I plan on putting the new fuel pump in as soon as it gets delivered and didn't want to mess with a full tank...

lift the bed up a foot (doesn't have to come completely off), and do all the work between the bed and the tank, you wont risk breaking off plastic riser tubes or deal with heavy tank or or, if you have an 3/8 impact, a bottle of snake oil of choice (pb blaster, wd40, etc) and a T55 bit it is way way less risk and work to just loosen the bed all up, lift it a foot then block it off with a hunk of 2x4 between the frame and bed bottom. You don't even have to remove the rear wiring harness.

 

[JoshT]

With the new info, I'm going to agree with brain. Check your wiring out real good. Does sound like a somewhat imtermitten issue, or atleast varying degrees of inaccuracy. That could definitely be related to bad connections, wires, and grounds.

Since you already have the Bosch ordered and they've said that they'll take the problem unit back, I'd install the Bosch and take the problem unit back. Even if it is a connection or ground issue the problem may be related to the wiring of the sending unit itself. I don't think anyone would tell you that the Bosch isn't an all around better unit than the house brand you have now, I just caution that you may still have to adjust the float to get it reading correctly (aka calibrated).

 

[flyin-lowe]

lift the bed up a foot (doesn't have to come completely off), and do all the work between the bed and the tank, you wont risk breaking off plastic riser tubes or deal with heavy tank or or, if you have an 3/8 impact, a bottle of snake oil of choice (pb blaster, wd40, etc) and a T55 bit it is way way less risk and work to just loosen the bed all up, lift it a foot then block it off with a hunk of 2x4 between the frame and bed bottom. You don't even have to remove the rear wiring harness.

I may have been a little confusing. I did and plan to move the bed. last time I changed the fuel pump the tank was 100 % full. I had just topped it off to see if the seal was leaking. I would rather change it with the fuel lever lower so I can peak in and make sure there is nothing going on inside the tank causing part of the problems. I don't think there is but I would like to try to make sure there isn't anything going on in the tank that is interfering with the float.

 

[Brain75]

...I forget which is which, but if it goes way past full or way below empty and sticks, you have a short or no ground. one is no resistance, the other is infinite resistance, and if you are familiar with the vehicle you will know what is past the end of the normal range easily.

That is another test you can do when you have the bed up/off, with the wire disconnected from the sender, turn the key to run and the gauge should peg out and go past full or empty, then ground out the sender lead and (after a few seconds due to slosh module) it should peg out the other direction full or empty - checking to make sure the gauge is good, and after you find your bad ground that the wiring is all working correctly.

 

[JoshT]

Since we're talking tests you can do with the bed off, you could try checking your new sending unit before you install it. You'll need an extra set of hands, but with the sender out of the tank, move the arm slowly and watch the gauge to make sure it sweeps properly. The slosh module slows response, but it should still register the sweep if you don't move too fast. If you do this, pull the fuse for the fuel pump so it won't be trying to run dry.

 

[SenorNoob]

That sounds similar to what mine did when I first got it. I found a pinhole in the brass float that slowly sank over time and part of the plastic housing of the sender was missing allowing the wiper of the sensing unit to float away from it's resistor.

 

[flyin-lowe]

So this morning I finally had time to install the new Bosch unit that I ordered. Not sure if it was just dumb timing or not but as I was backing the truck into my pole barn the CEL came on. Hooked up the reader and it was P0463 (fuel level sensor circuit high input). When I took the oldl unit out I imediately found the float and arm was laying in the botom of the tank. Not sure when it came off because the gauge was showing (and stilled showed) 1/4 of a tank of fuel which was fairly accurate. Not sure if it came off a couple weeks ago when the gauge started going haywire or not? I am not sure if the arm where the float hooks into was floating a little and that kept it at 1/4 tank or not. Anyway while we had it apart I checked the plug and it appeared at this point in time the ground was good. So I installed the new Bosch unit appeared to go to the right position and I took my test drive and filled the tank up and the gauge went to full. Now to put some miles on it and pray this ends my couple month pain in the A$$ dealing with this issue. Fingers crossed.

 

[flyin-lowe]

Last update (I hope) on this old thread. Finally put some miles on the truck. We drove it to 294 miles and the gauge showed just under quarter tank left. Filled it up and it took 15.56 gallons so this tank we got 18.9 mpg’s. Plus with the 19.5 gallon tank each quarter tank is 4.8 gallons. So since it had 4 gallons left the gauge is as close as I could expect. We’ve had 250 lbs of weight in the back during this time so it might get a little better mileage once that’s gone. So far so good

 

[pjtoledo]

a bit late to the party,
from a 2004 manual: low fuel is 22.5 ohms, fuel high is 145 ohms.

the instrument cluster micro processor/slosh module monitors the voltage between the PCM and the tank