PhotoVette1

When the fuel gauge on my 1977 would read "E" and the low fuel light would come on, the tank would only take about 12 gallons--leaving 5 gallons effectively unusable due to the fact I had no way to know how much fuel remained in the tank if I continued to drive.

I did a few tests and determined that at "E", the fuel gauge sending unit was sending a 23 ohm signal to the fuel gauge.

What I did is to add a 10 ohm resistor inline and boasted the signal from the sending unit.

Now when my gauge reads "E" and the low fuel light comes on, I have 2 gallons remaining in the tank instead of 5--what the factory manual calls for actually. This effectively increases my range about 50-60 miles (without wondering if I'm gonna run out of gas that is!)

Here is how I did it--no cutting of wires required.

1. Search over the driver side muffler and locate a fat black cylinder-shaped rubber wire connector--connecting 2 wires. This is the connector for the fuel gauge sending unit.

2. Pull it apart.

3. The wire port shown in diagram is the one you want to add resistance to.

4. Make-up resistor wire patch as shown.

5. Plug in the patch. Tape and secure.

Done--a fifteen minute job.

45ACP

Did you find that the gauge movement is linear now - 1/2 tank really is 1/2 tank, 3/4 reading is now correct?

What do you mean by "boosted the signal from the sending unit"? Do you mean the added resistance?

The problem with my gauge is that it will register full forever, only to have it plunge while burning off the last few gallons. The only way to keep tabs of things is to note the miles travelled.

Techno

Nice post.

Its easy. Its exactly a smidge below E.



I have to say though that you and me are a unique group of people who wish to use the tank of fuel rather than fill it at 1/2 or 3/4 or whatever.
Ever meet one of these people? They are actually proud of the fact they tote so much dead fuel around.
" I always fill it up at 3/4 of a tank".

PhotoVette1

I do a lot of long distance highway driving in my 'vette; it's nice to have the extra range and/or piece of mind.

Yes, it's a linear fix; just as the needle touches 'E' the low fuel light goes on and I know I have almost exactly 2 gallons remaining--just as GM intended but never delivered on.

PhotoVette1

Yes, at 1/2 tank it'll take 8 gallons at the pump--close enough with a 17 gallon tank.

What you have is a bad ground--measure the ground resistance at the plug I mentioned--the sending side should read somewhere between 13-90 ohms depending on fuel level, the ground side should read 1-3 ohms.

45ACP

Excellent. Thank you.

hunt4cleanair

Hey Photovette...nice work!

Couple of thoughts...comments.

You must have the ZX2 Convienence group which I believe included the LOW FUEL light for 77.

Second, in 78, we went to a 24 gallon tank. I've run my tank pretty dry to prepare for removing and rebuilding the fuel tank sending unit. Once I cleaned up the contacts I did a bench test of the potentiometer and observed as I moved closer to "E" the OHM needle moves quicker than when I start at the "F" end of the pot. But for a 24 gallon tank, would the resistor needed vary from you determined for the 17 gallon tank?

I noticed that my LOW FUEL light comes on with five gallons remaining in the tank while "E" is probably about eight gallons.

PhotoVette1

Then the fix will work for you perfectly. Measure the resistance at the point when the fuel light goes on, and then place a 6 ohm resistor in the circuit as described. The fuel light will go off and the needle will be more toward F. Then drive it until the fuel light goes on again and see how much gas is left when you fill up. If more then 2 gallons, add more resistance. I have fine tuned mine until I have exactly 2 gallons remaining when the fuel light goes on.

You'll have 6 more gallons of measurable gas in your tank.

KenSny

Sorry, but I have to chuckle.....

You guys and your constant quest to make idiot lights smarter! I guess us old folks with cars that don't have those things are always popping into gas stations every block or so, in fear of running out of gas.

PhotoVette1

It's also about not wanting the fuel gauge to read E when I still have 5 or 6 gallons in the tank. With a 17 gallon gas tank, that only gives me about 10-11 gallons of useable fuel--which may be fine for a Toyota Echo, but this is a Vette we're talking about here!

Now I have 15 gallons of measurable fuel and that gives me a greater peace of mind and reduces stress--I travel a lot to areas where gas stations are few and far between.

I actually drove 1.5 hours on my fuel light and gauge reading E before I found a gas station open. Along the way there were signs posted that read, "Red Wolf Protection Area", and "Black Bear Crossing". Not the thing to see when you're in the middle of nowhere at night and hadn't seen another car for hours! Of course, I had run out of cigarettes too, so those wolves would probably have gotten their butts kicked if they had bothered me.

Engage

How can I correct a guage that reads 1/4 and is actually empty?

Barry

PhotoVette1

Take a reading at the fuel level sender plug where it goes to ground--it should read near 0 ohms. If it doesn't read close to 0 ohms, then redo the level sending unit ground. If it reads close to 0 ohms, you can add a resistor on that side. Then, if the gauge does not go down closer to E, it's a gauge problem.

rosslato

nice work photovette. i'm w/you, nice to know exactly how much gas you've got

jeffmcgill

Do you take the reading when the tank is full? empty?
Also ( i'm a real novice) is the sending unit on top of the tank? Do you need to drop the tank in order to access it?

any help will be appreciated

Gale Banks 80'

Considering that the Float in the Tank is easy to bend how do You figure that into this ? So You are emptying the tank and then looking to see that the float is all the way down and the pot is at the end of its movement before adding the resistor ?
If the Float is out of adjustment, and a you add a resistor to correct it at empty, I would assume that the Gauge would be off for the rest of its travel.

Vince73

Question..

I installed a new fuel gauge in my 73 Vett, no change, the gauge did not move so I hooked up a new sending unit (not installed in the tank yet).. the gauge started working!!
But the calibration is way off, when full it reads only half a tank on the gage, when empty it is below the Empty line by the same distance as between the E line and 1/2 full.. As I move the pick up float up and down the Gage moves correctly but is off by half a tank?? Is there a way to adjust the needle position at empty and at full?? (hopefully without pulling the dash apart again.. that was a lot of work to put back together
Thanks!!