Purchased new fuel sending unit...working incorrectly.

[ilyafish]

My previous fuel sending unit was bad.  The way i checked it was by taking the ground and touching it briefly to the positive (which made the fuel gauge spike, which obviously means the gauge works, sending unit is bad).  I purchased a new sending unit from US Coach.  I put it in, and it was first giving me an empty reading on a pretty empty tank, so i assumed it works.  However once i started driving it went up to half a tank....only to have my bus run out of fuel on the way to the truck stop (boy was that a fun adventure!).  Anyways, it pretty much shows a half a tank just about always (granted since i run off WVO from a separate tank i never put more than 20 gallons of diesel in) but the guage fluctuates so much and is so inconsistent, i know for a fact i am not getting a good reading.  i checked the ground, the ground is good.  If i pull the sending unit out and move it by hand, the fuel gauge reads full when in the full position, and empty when in the empty position.  Is there something i am missing?

[ol713]

   Check to see if your fuel tank is grounded.
                       Good luck 
                   

[NJT5047]

20 gallons is 'empty' for an MC9.  Generally, the sending unit must be set by moving the float on the arm.
Still, 20 gallons is run-out territory.   I believe the last 25 gallons is considered unuseable in an MC9 tank.
Add some more fuel.  I'd recommend keeping about 40 gallons.   And never park with the drivers side down when low on fuel. 
The sender can be tested by removing the sender from the tank, attach a ground wire to one of the mounting screw holes and attach the sender lead to the center terminal.  Move the arm from extreme lowest to the max height...the gauge should follow the motion of the sender. If it doesn't....back to the drawing board. 
One problem could be related to the resistance range of some gauges.  They vary.  You may have a mismatched sender/gauge.   
Still, you could have a badly adjusted float on the sender arm.  Check for linear movement from minimum to maximum sender.  If you have that, everything's working and the sender must be set. 
With 20 gallons of fuel, it should be reading 'bone dry'....empty should be set to about 35 gallons. 
HTH, JR

[niles500]

Bite the bullet and top off your tank - then add 20 to 40 gallons at a time to keep it topped off - you just eliminated at least 3 possible headaches IYKWIM

[Gary '79 5C]

As mentioned previously, I would not rule out a mis matched sender / guage resistance. Not sure if your guage was orig equip. but I would start there.
My PO had two fuel gauges installed, with the thought of a second tank, but never installed. I tried to switch the sender to the "spare" guage, and No Go. Different resistance. Not sure why they would install different guages, but changed out guage location, and matched sender/guage. All better.

Also, you will need additional fuel sometime, so if you top off, you might take the time to fuel, stop at 30% full, 60% full, and check guage thru out span.
Obviously, full tank = full  needle deflection.

Talk it thru with Luke and crew, they will assist.

Gary

[pvcces]

Since we take readings of our fuel by dipping the tank using a hose and a long 1/4" bolt, it is easy to see how much fuel is in the tank, as long as the coach is level side-to-side. Compare the dip reading with the gauge and you will know if the guage is accurrate.

For what it's worth.

Tom Caffrey