<VV> LM Gas Gauge Inaccuracy

[Dave Thompson]

Tony's suggestions are very sound. However, here's several other things to
look at:

First:
When I worked at LS Corvair parts early this year, we would order a bunch of
sending units at one time. They usually arrived all shoved into one box. The
first one that I ever sold was to a local guy that I have known for a few
years. A few days later, he came by and told me that the float wire was bent
so as to give a bad reading. He showed me which one was correct on my shelf.
We found two other ones with bent arms. I straightened the arms and put them
back on the shelf. I inspected all subsequent orders and had to straighten
one or two before putting them on the shelf. 

Is your sending unit new? Could it be bent down?

Second:
Many old factory floats get a hole in them and fill with fuel. Sometimes,
the hole is very small and the float only partially fills. This allows the
float to semi-float but not go all the way up, giving a bad reading. Some
venders sell the sending unit and float separately. If replacing the sending
unit, replace the float too. While you are at it, replace the strainer
"sock" at the same time.

Lastly:
If you do remove the sending unit, replace the o-ring type seal. They are
only a couple of bucks and will help make sure that you don't have a leak
later.

Dave Thompson

-----Original Message-----
From: Tony Underwood [mailto:tony.underwood at cox.net] 
Sent: Sunday, September 20, 2009 7:44 AM
To: virtualvairs at corvair.org
Subject: Re: <VV> LM Gas Gauge Inaccuracy

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..