1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

Fuel Gauge Question

Discussion in 'Early CJ-5 and CJ-6 Tech' started by tcfeet, Sep 8, 2017.

  1. Sep 8, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    1964 cj5 , almost stock.
    Trying to get fuel gauge on the cluster to work. Replaced the sender unit and checked it with a meter.
    The generator has been replaced with an alternator, so there is no voltage regulator left.
    The question is: Do I need to add a resistor for the gauge to work, and if so, how do I do that??
     
  2. Sep 8, 2017
    Twin2

    Twin2 wasn't me Sponsor

    Virginia Beach, VA
    Joined:
    Apr 28, 2011
    Messages:
    3,542
    have you tried to ground wire that goes to tank sender , and see if gauge will move .
    also does water temperature gauge work
     
  3. Sep 8, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. Sponsor

    cordele, Ga.
    Joined:
    Mar 29, 2007
    Messages:
    5,249
    No resistor to the fuel gauge. The gauge voltage is regulated from inside the gauge itself. If you ground the wire going to the sender, the gauge should move to full. If it does then like said above you may not have a good ground on the sender.
     
  4. Sep 8, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    Temp gauge does not work, but I had installed a mechanical temp gauge to use instead.
     
  5. Sep 9, 2017
    Twin2

    Twin2 wasn't me Sponsor

    Virginia Beach, VA
    Joined:
    Apr 28, 2011
    Messages:
    3,542
    as walt said . gauges is controlled by a internal voltage regulator inside of fuel gauge , if it burns up . both gauges will not work
    biggest issue with regulator. is cluster must have a good ground . before applying 12 volts to it
    the replacement fuel gauges you see online . aren't for a early cluster JMO
     
  6. Sep 9, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    I grounded the sender wire and the gauge moved to full.. I then grounded the sender directly to battery and nothing.
    Then I grounded the cluster housing directly to battery and still nothing..
     
  7. Sep 9, 2017
    Twin2

    Twin2 wasn't me Sponsor

    Virginia Beach, VA
    Joined:
    Apr 28, 2011
    Messages:
    3,542
    that tells me gauge is good . must be a bad ground on sending unit . check there . if still doesn't work replace
     
  8. Sep 9, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. Sponsor

    cordele, Ga.
    Joined:
    Mar 29, 2007
    Messages:
    5,249
    So if your sender is good then you are not getting a good enough ground from the sender housing to tub/frame connection.
     
  9. Sep 11, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    Took sender off, re-checked ohms. ok. Cleaned up ground to sender, nothing. Wire to cluster ok.
    One thing I'm wondering about, when I ground the wire from the cluster to sender, the needle hesitates and jumps
    just a little. Then moves to full on the gauge. Maybe the needle is hanging a slight bit on empty and the sender
    does not have enough resistance to push it over?
     
  10. Sep 11, 2017
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    19,231
    Be careful grounding the sender wire. The tank unit has at least something like 10 ohms resistance, and when you ground the wire you are putting more current through the gauge than it's designed for. Also don't test the gauge without a ground from the cluster to the dash. The on-off "voltage regulator" in the fuel gauge will not cycle without a ground, and you'll burn up the gauges.

    I suggest using a 7805 VR in place of the VR in the gauge. They are cheap, very reliable, and just go open if the ground pin is not grounded. I did this to my J20 and it works very well.
     
  11. Sep 11, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    What is the"7805 VR".
     
  12. Sep 11, 2017
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    19,231
  13. Sep 11, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. Sponsor

    cordele, Ga.
    Joined:
    Mar 29, 2007
    Messages:
    5,249
    If you want a very simple test to verify your fuel circuit then do this.
    Remove the ignition wire from the + (plus) terminal on the coil so you won't burn points during test.
    Turn ON the ign key.
    With a test light connect the alligator clip to a good ground and the pointy end on a known battery hot connection to confirm good tester and ground.
    Put pointy end on center screw at fuel tank sender (with sender wire connected) and note that the tester light flashes OFF and ON.
    This tells you the fuel gauge regulator is working as needed.
    Note that the fuel gauge will slowly move to full as the test light flashes.
    Now put the pointy end to the metal cover of the sender housing.
    If the test light flashes this tells you that you have lost ground.
    Repair ground.
     
    Last edited: Sep 11, 2017
  14. Sep 11, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    Thanks for the info. Will proceed with the test tomorrow.
     
  15. Sep 16, 2017
    tcfeet

    tcfeet Member

    east of west,...
    Joined:
    May 30, 2009
    Messages:
    264
    Ok, the problem with the gauge was the needle was rubbing on the bezel enough that it could not move.
    Reworked the lower edge to give clearance and this 53 year old gauge went back to work. [stewart warner]
     
  16. Sep 16, 2017
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    19,231
    Excellent!
     
  17. Sep 16, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. Sponsor

    cordele, Ga.
    Joined:
    Mar 29, 2007
    Messages:
    5,249
    Glad it's working. :D
     
  18. Dec 4, 2018
    TonyM

    TonyM New Member

    Middle Tennessee
    Joined:
    Jul 30, 2017
    Messages:
    34
    digging up an old thread after searching for a bit.... I have a '56 CJ5, F-134, 6v neg ground system... Grounding my fuel sending unit from one of the mounting screws to the tank does not initiate a reaction on the gage regardless of where the ground wire goes to ground (body, frame, battery, etc). If I ground from the sender wire connection point the needle moves to full (the tank is full). Will grounding from the sending wire connection harm the sender or gage? Not sure what sending unit the PO put in the tank and the gage appears to be original/stock in the speedo cluster. Haven't driven enough to see if the gage moves toward E due to fuel consumption. Will try to manually move the float in the tank tonight to see the gage reaction, but I didn't want to mess with all of this hooked up this way if it's gong to burn up the gage or sender.
     
  19. Dec 4, 2018
    PeteL

    PeteL Member Sponsor

    Hills of NH
    Joined:
    Aug 3, 2003
    Messages:
    5,937
    Sounds as if you are grounding the gauge directly, bypassing the sending rheostat in the tank. That won't give you actual readings of the fuel level.

    But it seems to show that the dash gauge is working. In which case, possibly the sender is failed.
     
  20. Dec 4, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    19,231
    The sender in the tank is a variable resistor. This resistor ranges from (typically) a low of 10 ohms to a high of 70 ohms, depending on the application. When you ground the sender wire, there is zero ohms between the gauge and ground. This could damage the gauge if left connected. Touching the wire to ground won't hurt anything, as long as you don't leave it that way. Gauge movement shows that the gauge is working.

    Use your multimeter and measure the resistance from the connector that goes to the tank to ground. If the sender is working, the resistance you measue will be proportional to the amount of fuel in the tank. If the resistance is infinite (open), either the sender is broken or the tank is not grounded to the Jeep. The proper resistance for the sender is in the FSM.
     

Share This Page

New Posts