Topic: Fuel Gage operation


Derby    -- 01-19-2022 @ 10:55 AM
  I would appreciate a detailed description of the operation of the fuel gage and sending unit. Does anyone know of a good source or article? My car is a "37 if that helps.


TomO    -- 01-19-2022 @ 5:23 PM
  Here is a link that has the description:

http://www.norgv8club.org/all-dcouments-indexed/category/15-service-bulletins

If you are having a problem, please describe the problem and we may be able to help you diagnose it.

Tom

This message was edited by TomO on 1-20-22 @ 8:20 AM


Derby    -- 01-20-2022 @ 5:18 AM
  My car has been converted to 12 volt negative ground .configuration. I am trying to get an accurate calibration. The fuel tank sending unit is from Dennis Carpenter. The sending unit specification is: FULL, 16 OHMS empty is 91 OHMS.. I have checked the sending unit in car reads 46.8 OHMS. All seems OK. I need to understand the gage system to do a full analysis. The gage has a voltage reducer to 6V with leads switched to gain a correct polarity. What type of gage is it?

Many thanks for any help


Derby    -- 01-20-2022 @ 6:12 AM
  I now have a good description of the operation of the system. Thank for all the help!


1937sedandelivery    -- 01-20-2022 @ 7:03 AM
  Tom,
How do I use your link to access the pdf?
Thanks,
gregg


37RAGTOPMAN    -- 01-20-2022 @ 7:18 AM
  HI Derby
I think you might have to bend the float arm to match the distance from bottom of tank to the top to get a
accurate reading,
you can do this by measureing your tank, with sender removed [ MEASURE TANK ] and recreate it outside of the tank and watch the gauge and see what it reads,
not a fan of the repro parts., good luck
my 2 cents 37Ragtopman,MAINE


TomO    -- 01-20-2022 @ 8:24 AM
  Gregg, I have updated the post to reflect the correct link. When you get to the web page look for 'Ford Bulletins Descriptions.PDF' . I did not realize that when I opened the file the link would point to my computer. Sorry for the confusion.

Tom


1937sedandelivery    -- 01-20-2022 @ 8:44 AM
  Thanks Tom.
Wow, that pdf is full of good info. That website looks pretty cool too, will keep it handy.
gregg


JayChicago    -- 01-20-2022 @ 11:28 AM
  Derby said: "The fuel tank sending unit is from Dennis Carpenter."

You have an aftermarket sending unit. They will work somewhat, but are notorious for giving inaccurate readings on the gauge. They use a variable resistor. The original sending unit used a pulsing signal. Totally different technology. It will take some effort to get your aftermarket sending unit to be usable.

Step 1
Adjust the float arm as best you can as described by 37RAGTOPMAN. You want the float arm to hit the stop on the sender just before the float would hit the top of the tank, and float arm to rest on bottom stop on sender just before float would rest on bottom of tank.

Step 2
Add resistor(s) in series with the wire to the sender. You can add the resistor right ahead of the sender; is easier to work there than behind the gauge. (to avoid cutting and splicing into my original wire, I rigged a couple eye connectors on the resistor, then shrink wrapped that assembly) What size resistor? Will have to be determined by trial and error. Depends on your particular sender. 7 ohm worked with the aftermarket sender in my car. I got to 7 ohm using three 22 ohm resistors in parallel.

Even with this, I doubt you can get accurate readings full scale. I was able to get the gauge to read empty when the tank is empty. With a full tank, gauge needle stays pegged full until the tank is about 3/4 full, then needle finally starts to move down. But I feel accuracy near empty is the only thing that is important.


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