gas gauge problem
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
http://forums.corvetteforum.com/show....php?t=1574491
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
http://forums.corvetteforum.com/show....php?t=1574491
This is good fix for a float unit that is corroded and does not work as was originally designed. So cleaning it up will get you back to square 1 but does not address the real problem of a normally working, non-linear fuel gauge.
This is a piece that I wrote several years back to increase the accuracy of the fuel gauge.
Tired of not having the gas gauge drop as you use gas. The inaccuracy was to much for me to stand so I investigated the problem. According to specs the float unit has a range of 0 to 90 ohms. I measured 20 to 110 ohms on my float unit. The 20 ohms representing the empty end and the 110 representing the full side (most other cars the low represented full but in the digital world they can do what the want).
The basic problem is the resistance doesn't not drop fast enough as gas is removed from the tank. I had to move the float arm to the 65 ohm point before it would indicate a one bar drop on the gas gauge. 75 to 110 ohms read full. It was not before I got down to about 37 ohms that I got a half tank indication on gauge. In reality the float resistance range is not properly matched to the electronics in the CCM. How to fix properly, you can’t unless you rewind the float wires (I don’t think so). So the best you can do (rather than redesign CCM) is to compensate for the problem. Make the resistance read lower faster as gas is burned. I added a 180 ohm resistor (yours might me slightly different) across the float unit, this will accomplish this. To little resistance and you will not get a full reading, to much and you are giving away accuracy which you a targeting in on. If I really really fill my tank I can get a full indication, if I let it click once or twice I might get a one bar down. I’m on the edge and I can live with that. But I do get more accurate readings right down to ¼ tank. Its not perfect, but I’m within 2 gallons or less when I get gas.
All you need to do is to add the resistor across the tank wiring. You do not need to take out the tank unit. Just remove the gas door and the rubber boot. Come back 6 inches or so from the tank unit and skin back the black and purple wires. I did not cut the wires, just removed about ¼ inch of insulation, wound the resistor ends around each wire and tape it up. I don’t think I soldered mine because I was not sure of the resistor I wanted to use and how the whole thing was going to work out so wanted the option of removing it easy. So temporary became permanent 3 years ago. Hope this can be of use to some of you.
P.S. - There are 3 wires. Black is ground and gray is power for the pump and the purple wire is the float unit.
This is good fix for a float unit that is corroded and does not work as was originally designed. So cleaning it up will get you back to square 1 but does not address the real problem of a normally working, non-linear fuel gauge.
This is a piece that I wrote several years back to increase the accuracy of the fuel gauge.
Tired of not having the gas gauge drop as you use gas. The inaccuracy was to much for me to stand so I investigated the problem. According to specs the float unit has a range of 0 to 90 ohms. I measured 20 to 110 ohms on my float unit. The 20 ohms representing the empty end and the 110 representing the full side (most other cars the low represented full but in the digital world they can do what the want).
The basic problem is the resistance doesn't not drop fast enough as gas is removed from the tank. I had to move the float arm to the 65 ohm point before it would indicate a one bar drop on the gas gauge. 75 to 110 ohms read full. It was not before I got down to about 37 ohms that I got a half tank indication on gauge. In reality the float resistance range is not properly matched to the electronics in the CCM. How to fix properly, you can’t unless you rewind the float wires (I don’t think so). So the best you can do (rather than redesign CCM) is to compensate for the problem. Make the resistance read lower faster as gas is burned. I added a 180 ohm resistor (yours might me slightly different) across the float unit, this will accomplish this. To little resistance and you will not get a full reading, to much and you are giving away accuracy which you a targeting in on. If I really really fill my tank I can get a full indication, if I let it click once or twice I might get a one bar down. I’m on the edge and I can live with that. But I do get more accurate readings right down to ¼ tank. Its not perfect, but I’m within 2 gallons or less when I get gas.
All you need to do is to add the resistor across the tank wiring. You do not need to take out the tank unit. Just remove the gas door and the rubber boot. Come back 6 inches or so from the tank unit and skin back the black and purple wires. I did not cut the wires, just removed about ¼ inch of insulation, wound the resistor ends around each wire and tape it up. I don’t think I soldered mine because I was not sure of the resistor I wanted to use and how the whole thing was going to work out so wanted the option of removing it easy. So temporary became permanent 3 years ago. Hope this can be of use to some of you.
P.S. - There are 3 wires. Black is ground and gray is power for the pump and the purple wire is the float unit.
Last edited by pcolt94; Apr 18, 2007 at 03:01 PM.
Instructor
Joined: Apr 2007
Posts: 105
Likes: 0
From: FL
OK, i removed the unit from the tank, removed the resistor block (held in by the 2 torx screws), then cleaned it all using a small peice of scotch brite to get the gunk off. I also cleaned the wiper, if that's what you call the peice of metal that rubs the resistor. Also cleaned the small spring that makes contact with the resistor block and unit. I tested it outside the tank to see if it worked now (unplugged the fuel pump!). It now reads great! i had to put a new sock on the pump because I bumped it and it ripped. Total cost= $8.00. I'm extremely happy now! Thank God for this forum!! All you knowledgeable people are great!
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