Hi,
I just bought a 1993 and I have filled the tank twice and I've noticed that it stays on the full mark for a long time and then all of the sudden it's reading near a 1/2 tank full and it's really close to empty. Would this be a bad fuel tank sender or what?
Hope someone can enlighten me how to check this out, for sender/fuel pump units are expensive.

Thanks,
John

 

the fuel sender unit has a simple rheostat built in - either the "float" is hanging up and catching on something IN the tank, or the rheostat (in-tank) is corroded and not sending out the proper resistance. Finally, the wiring to the dash could be faulty.

Based on your symptoms, I would gander that you need to take some brake cleaner to the in-tank rheostat.

 

Actually under normal operation the fuel gauge stays high for a long time however your situation may be a little worse. If you remove the tank unit you can use some fine emory cloth or sand paper to clean up the float unit wipers and coil wire contacts. I would first measure it to see if the resistance is smooth when moved.

My fuel gauge was an absolute mess, no bodys could be worse. I found out after I bought the car that it had been sitting for almost 2 years and probably with low fuel where the fuel did not cover the sending unit. It was real nasty took me hours to fix. I actually ran out of gas on the way home from the dealer. Thats how it knew it was really a 20 gallon tank.

I have a thread with some detailed information on the fuel gauge and how to make it read more accurate.

http://forums.corvetteforum.com/show....php?t=1373669

 

High sulphur content in fuels seems to be the popular culprit for bum gas gages and the last Google Search I did for "Bad Gas" had Shell Oil on the losing end of most of the Class Action Lawsuits that have been brought over this issue. They did mix up a particularly gnarly batch at one of your Gulf Plants that found it's way to Florida about two Years ago and one of our members got them to spring for a new sender. You might see if anything is going on in your Area, particularly if you use Shell gas.

 

There are several factors at work here, as some have been mentioned above.

The C4 fuel tank volume is "non linear" -- the top half of the tank has more volume than the bottom half.
And, the fuel tank gauge rheostat is "linear."
Therefore, they aren't a good match.
So, when the fuel gauge reads a linear half way, you have the volume of the smallest half left.

Here is how I view my fuel gauge reading:
When it starts to move down from full = half tank
half tank = 1/4 tank
1/8 tank = you better be at the gas station now


Tom Piper