<VV> LM Gas Gauge Inaccuracy

[Tony Underwood]

At 10:21 AM 9/20/2009, Jay Pitchford wrote:
>When gas gauge reads empty, it stops filling at about 9 gallons, but the
>dash gauge reads 3/4 full. Do I replace the tank hardware ? What should I
>look to replace first? Thanks!!



Sending unit most likely...

...but change it out ONLY after you unplug the wire to the sending 
unit and ground it to a GOOD chassis ground, and check the gauge to 
make sure it reads empty.  If it does not, don't replace the sending 
unit, replace the gauge.

Now, that being said:


The 3/4 full figure when the tank is topped off almost sounds like 
someone earlier on replaced the tank sending unit with the wrong 
type, such as an early 'Vair tank sending unit which IS 
different.   Got an ohm meter?   A good one?   You can check the 
sending unit yourself.   Earlies will read between zero and 40-50 
ohms depending on whether it's reading <empty> or <full>.   Lates 
will read around zero to 80-90 or thereabouts.

If your gauge reads wrong when the tank is full and the sending unit 
resistance measurement (from the connector pin on the sending unit to 
ground) reads around 80-90 ohms, the gauge is likely defective.

Also, unplugging the wire from the sending unit should pin the fuel 
gauge past full whether there's fuel in the tank or not.   If the 
gauge does not pin to the right when the sending unit wire is 
unplugged, the gauge is likely bad.



Now that I've muddied the waters considerably, hopefully someone else 
will pop in and provide a more useful solution.





tony..