When my fuel gauge reads "E" there's still 5 gallons left.

Now, the sending unit maxs at 90 ohms and goes down to 13 ohms. At "E" on the fuel gauge, it's sending 22 ohms however.

Can I put a 10 ohm resistor in line so when the sending unit sends 13 ohms (the lower limit of the sending unit), the fuel gauge and fuel light will think it's 23 ohms and thus read correctly?

 

That sounds right but most gauges don't read empty when the tank is empty. I've owned only 1 car that was empty on empty and it sucked.

Of all the cars I've owned ran out of gas in all but 1, 2 if counting the present one but there is always hope
The needle in most cars goes below empty and still has gas to get to a gas station, for the idiots among us

What will it read when full?
5 gallons isn't all usable in the tank either. I poured 5 into mine to start it and then had to drain it. Wouldn't drain out with the back jacked up.

 

The slant of the tank puts the lowest part at the foward-most part of the tank. The pick-up is towards the rear.

 

is the float new??? is it adjustable ?? iv'e never added a resistor

 

I'm going to try it--the owners manual states that the low fuel light should come on at "2 gallons". Mine comes on at 5 gallons remaining.

With a 17 gallon tank, a couple extra gallons of range would be nice.

 

Yes, you can alter a gauge reading by adding a resistor.
You might want to clean connections, a pencil eraser works on the gauge cluster connector & try Gumout in the gas tank.

I checked the accuracy of the 77 gauge when new by runnning it to just before E, pulling into a gas station & idling it out of gas.
It was accurate!

 

will this make it show less than full when full? Not that thats important. Just curious.

 

Good point. That's why I'd adjust the float rather than kludge up the electronics.

 

I have the same issue with my fuel guage. I thought it was the gauge at first, but it happened with 3 other gauges from different years. I have 8 gallons left as soon as it hits E.

 

My car never runs out! I've let it get below E before, and never had a problem. In order to get her to show full, or a tad over the F mark, I have to fill it right to the filler neck.

I pulled the bladder out of my tank, expecting to find that it had seperated from the tank. Reason being that I never could get more than 12 gallons in the car. The bladder in the tank was intact though, and now, knowing this, I'm not afraid to let it get below empty.

12.5 gallons fills it from E so that coincides direclty with your car having 5 gallons left at the same point. At least it's accurate and predicatble.

 

An extra resistance added will provide a constant offset.
When full, the guage will read more than full.
Addign the resistor will have exactly the same effect as bending
the float rod - with the convenience of easy access to change/adjust.

I'd look for a 10 Ohm potentiometer - so it can be adjusted.

 

Or just reposition the needle.

-Mark.

 

But if it lowers the "low" reading, wouldn't it lower the "full" reading also??

 

Would an early C3 tank fit? They hold 20 gallons. Later when the gas filler tube was modified to only accept the narrow diameter gas pump nozzles, the filler tube was lengthened so that the tank would only hold 18 gallons; the lengthed tube created an air space when you filled the tank. The air space reduced capacity from 20 to 18 gallons. Apparently the plenum ate up another gallon of capacity in later C3's.

 

His reading is coming in low - too soon. It will raise the low reading.
It will also raise the "full" reading the same amount.

Moving the needle will not remedy his issue of a "Low Fuel" idiot light.

I'm just worried that too much added resistor will never allow the
guage to read "E" ... potentially running dry. It should be run dry, add as much
gas as you want for the warning light to come on ... then tweak the
potentiometer 'til the Low Fuel light just comes on.

 

That sounds pretty good. Being able to tweak the final result is a cool idea.

This must be a fairly common thing with the ole' Vette gas gauge. Mine probably has around 5 gals. on E too.

 

I'm gonna try it then--I'll run the fuel out until it's a the point where I know it has 5 gallons left---then wire it in line at the rear connector.

It'll be like adding 2 or 3 usable gallons to the tank!

 

is it weather proof???

 

isopropyl alcohol works great on electrical connections too

 

Adding resistance will change the reading on the gauge across the entire range of the gauge. It is not needed to correct this problem with the gas gauge!

The sender, when pulled from the tank and held in your hand should read 0 - 90 ohms. If the sender is not reading 0 ohms at empty then you should make an adjustment in the stop! If you look at the potentiometer on the sender, there are two stops. One at the top and one at the bottom. You can slightly bend the stops to obtain a correct zero ohms reading if you are careful.

You might also unbend the three tabs that hold the potentiometer together and clean the contact where it rides on the variable resistor inside the unit. If it is dirty, it will not send a correct reading on output! This is likely not the problem with your unit though. Since a dirty contact usually sends a low output reading instead of a high output reading.

A bad float will read low.
A dirty contact will read low
A stop tab to high will read high.

Try bending the tab just a tiny bit to see if you can obtain the correct reading. Once you have the tab bent, install back in the car and check to make sure that you still have your zero reading before filling the tank with gas. If there is an obstruction and the reading is higher tan zero, bend the arm in an upward manner just slightly. This will allow the unit to reach the bottom "zero" reading when installed again.