Author Topic: '75 Eldorado Fuel Gauge  (Read 416 times)

Offline benji808

  • Posts: 103
  • Name: Benjamin M. Roach
'75 Eldorado Fuel Gauge
« on: September 29, 2021, 10:03:16 PM »
Fuel gauge always reads empty, with the red "low fuel" light on. It "rises" to right at empty when I start the car, then stays there. Unplugging the ground near the back of the gas tank causes the gauge to read off the charts high, as expected. Any simple things to check before I drop the tank and replace the float?
« Last Edit: September 29, 2021, 10:46:56 PM by benji808 »

Offline Matti R

  • Posts: 206
  • CLC Number: 33333
  • Name: Matti Roth
Re: '75 Eldorado Fuel Gauge
« Reply #1 on: September 30, 2021, 03:25:02 AM »
You can check if the resistance from sending unit is changing according to fuel level in tank. At least in 71 Eldo there is wire connector close to filler pipe. You can open the connector and measure then resistance to ground. It that works ok then the problem is between the connector and the gauge. If I remeber correct, the resistance should be between 0-100 ohms depending on fuel level.
Best regards,
Matti
CLC #33333
67 DeVille convertible Sudan beige
79 Seville
64 Sedan DeVille
66 Calais Coupe

Offline benji808

  • Posts: 103
  • Name: Benjamin M. Roach
Re: '75 Eldorado Fuel Gauge
« Reply #2 on: September 30, 2021, 03:04:30 PM »
That is helpful! Do you have a picture of where that connector is on your '71?

Offline V63

  • Posts: 1408
  • Name: W Link
Re: '75 Eldorado Fuel Gauge
« Reply #3 on: September 30, 2021, 04:55:49 PM »
The connection is behind the license plate door, plugs into the body with back up lights ...it’s a beige wire if memory serves.

Offline benji808

  • Posts: 103
  • Name: Benjamin M. Roach
Re: '75 Eldorado Fuel Gauge
« Reply #4 on: September 30, 2021, 08:45:09 PM »
Ok - found the brown wire. I haven't tried measuring resistance before, but I set the multimeter, and ran the + side into the brown wire and - side into a ground (I just used one of the rear light sockets). This gave me a readings ranging from 3-5 (ohms?). Putting two and two together from your post, and that I recently filled up (I'd estimate the tank is 50%-75% full) I'm guessing that the sender is the cause of the error, causing a constant low reading. Does that sound right?

Thanks! 

Offline Matti R

  • Posts: 206
  • CLC Number: 33333
  • Name: Matti Roth
Re: '75 Eldorado Fuel Gauge
« Reply #5 on: October 01, 2021, 12:26:00 PM »
You are right. Sounds like the float is stuck or something else wrong with sender unit if the resistance does not change.
Best regards,
Matti
CLC #33333
67 DeVille convertible Sudan beige
79 Seville
64 Sedan DeVille
66 Calais Coupe

Offline bcroe

  • Posts: 3893
Re: '75 Eldorado Fuel Gauge
« Reply #6 on: October 01, 2021, 11:23:01 PM »
Float fell off or is water (gas) logged.  Bruce Roe

Offline benji808

  • Posts: 103
  • Name: Benjamin M. Roach
Re: '75 Eldorado Fuel Gauge
« Reply #7 on: October 04, 2021, 05:03:05 PM »
Thanks for the thoughts! I ordered a new sender ($69 from Caddy Daddy), and will plan to burn some fuel to reduce tank weight then replace. Looks like it "should" be pretty straight forward...  ;D

Offline Big Fins

  • Posts: 1802
  • CLC Number: 22631
  • Name: John Serio
Re: '75 Eldorado Fuel Gauge
« Reply #8 on: October 04, 2021, 06:58:11 PM »
Depending on how far you go, plan on carrying a 5 gallon can to get you back home.

Every time I use my car I fill it to prevent moisture build up in the tank. Even if it's 5 gallons, I like to keep it full.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top.
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top.

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

Offline benji808

  • Posts: 103
  • Name: Benjamin M. Roach
Re: '75 Eldorado Fuel Gauge
« Reply #9 on: October 09, 2021, 05:59:04 PM »
Thank you all for educating me on this! I installed a new sending unit today (sourced from Caddy Daddy- seemed like best availability and price), and the gauge appears to be working properly. Was a bit of a bear to wrestle the tank back up myself, but me and the floor Jack managed. 😊

 

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