odd new fuel gauge
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
odd new fuel gauge
my old fuel gauge started bouncing so I got a new one. It followed the gas in the tank, just bounced around. I plugged the harness back in and started the car. The gauge went to full and the low fuel light came on. I don't remember how much gas was really in tank, but I think somewhere between half and full.
can the plug go in upside down?
can the resistor on the back of the gauge go on wrong?
what else could it be?
thank you for any help
can the plug go in upside down?
can the resistor on the back of the gauge go on wrong?
what else could it be?
thank you for any help
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
played with the gauge. ground at tank moves gauge to empty, remove wire from tank moves way past full (about 5 pm on clock dial). Plugging wire back into sender moved about 1/8 to 1/4 past full.
So it seems to be working, just moving more than the original.
any ideas?
So it seems to be working, just moving more than the original.
any ideas?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
With the key on.. the gauge should peg full when the ohms wire is removed form the sending unit.. and when the ohms wire is grounded out it should read empty.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
It works just as this gauge does.. shown in the video. If you watch this video you can usually figure out where the problem is based on what the needle tells you.
The only loop hole not covered in this video is the printed circuit board (and this is the reason we stopped the year application at 1976) The gauges work exactly the same.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
It works just as this gauge does.. shown in the video. If you watch this video you can usually figure out where the problem is based on what the needle tells you.
The only loop hole not covered in this video is the printed circuit board (and this is the reason we stopped the year application at 1976) The gauges work exactly the same.
Last edited by Willcox Corvette; Nov 3, 2012 at 09:04 PM.
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I think the issue is at the sending unit. Have you checked the sending unit ground?
If the gauge itself was missing a ground it would go to empty.
If you have an old flasher.. remove the ohms wire from the sender and run a wire to one side of the flasher terminal... then run a wire from the other terminal on the flasher to ground.. Turn the key on.. This should make the fuel gauge read just above 1/2 tank. If this works the issue is for sure the sender.
IMHO.
If the gauge itself was missing a ground it would go to empty.
If you have an old flasher.. remove the ohms wire from the sender and run a wire to one side of the flasher terminal... then run a wire from the other terminal on the flasher to ground.. Turn the key on.. This should make the fuel gauge read just above 1/2 tank. If this works the issue is for sure the sender.
IMHO.
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
flasher trick
great tip on the flasher trick, will try that tomorrow. Was going to hit junk yard for a sender from an 80's chevy, but that works better.
the ground is in place, but the terminal is a little rusty looking. I will clean it up too.
will post an update
the ground is in place, but the terminal is a little rusty looking. I will clean it up too.
will post an update
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
Update
Hooking sender wire to ground on tank shows same reading as hooking to sender. It is past full but not nearly as far past full as when sender wire is unhooked
Is gauge bad?
11/6/12: bought resistors from Radio Shack between 0 and 90 Ohms will try them tonight to see effect on gauge
Is gauge bad?
11/6/12: bought resistors from Radio Shack between 0 and 90 Ohms will try them tonight to see effect on gauge
Last edited by dburgjohn; Nov 6, 2012 at 05:53 PM.
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Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
testing
I guess I was expecting the needle to move from empty to full across that 90 Ohms, i.e. 45 Ohms being half a tank. I can live with it if it tracks a little father right of full as long as it does not bounce like the old one.
Racer
Joined: May 2011
Posts: 373
Likes: 6
From: Dover Delaware
odd new fuel gauge
Just wanna add a few words here...A very interesting post...I've been curious about my fuel gauge etc since I've had my 78(3 1/2yrs). Upfront I am not an electrical guru....just don't have that expertise....It always seems funny that when I do fill the tank it takes more gas than the needle is indicating its position on the gauge.....In short, after reading this post and the Wilcox paper I did find and removed the ohm wire with the key on and with a full tank the needle pegs about one inch past the "F"...May I assume that the fuel system is properly working with out any further testing so I don't have to send it over to my Vette expert??????
I am wondering if the OE fuel system parts are/were not all that accurate to begin with.....any and all comments etc are appreciated..
Thanks all and sorry for the long post..........
mk's78
I am wondering if the OE fuel system parts are/were not all that accurate to begin with.....any and all comments etc are appreciated..
Thanks all and sorry for the long post..........
mk's78
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 283
From: Dyersburg TN
I have always thought that fuel gauges were not linear in their movement. Several vehicles of different makes all behave in the same way, i.e. from full to half takes a while and half to empty zooms by. It should be no surprise since a float type sender is not a measure of volume, but height. For the change in height to be consistent as the drop in volume the tank would have to be a square, rectangle or vertical cylinder and completely level.
We have to accept that fuel gauges are relative devices not scientific instruments. You have to learn the behavior of each one to know how close to the 'E' you can get without having to walk home.
We have to accept that fuel gauges are relative devices not scientific instruments. You have to learn the behavior of each one to know how close to the 'E' you can get without having to walk home.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
The fuel gauge and electrical oil pressure gauges are linear.. 0-90 ohms with 45 being right in the middle. Temperature gauges are a whole different ball game.. and are non linear.
Most senders will actually go past 90 ohms around 91-95 and I've seen one at 98 ohms! This will really mess with your dash reading and give off the age old idea that the top half takes longer to go away. You also have to factor in the level on the sender and how accurate it is in relation to the amount of fuel in the tank. Definitely not a scientific instrument..
Most senders will actually go past 90 ohms around 91-95 and I've seen one at 98 ohms! This will really mess with your dash reading and give off the age old idea that the top half takes longer to go away. You also have to factor in the level on the sender and how accurate it is in relation to the amount of fuel in the tank. Definitely not a scientific instrument..
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
John.. it may be the sender in the tank that is off... The gauge I can assure you will be pretty close.. it's what the input is that defines the reading.