Fuel Gauge/Sender Problem

Discussion in '40- & 55-Series Tech' started by tkerkela, Aug 25, 2009.

  1. tkerkela

    tkerkela

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    I have a 76 FJ40 and I have an aftermarket RCI fuel cell and sender. I filled it up earlier in the week and there was just about 5 gallons of fuel or so in it and it was reading about 1/2 ot 3/4 of a tank. The thing is, the tank is 19 gallons. Something isnt right at all. Yesterday I filled the tank right up as much as it could hold and it read totally empty. I have no possible idea what it could be, its almost like its reading backwards or something. Help is much needed and appreciated.
     
  2. JB740i

    JB740i

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    Seems like the first thing is to always check the ground. I know nothing about fuel senders beyond that. But see if you can find the ground for the sender.
     
  3. dgangle

    dgangle total rice SILVER Star

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  4. nedhed

    nedhed

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    Fuel level senders in the fuel tank don't all work the same. Many aftermarket gas tanks use a GM 90 ohm sender. I'm not sure what the FJ fuel gauge is set up for, but it sounds like a mismatch between the sender and the gauge to me. I'm sure someone else can chime in and provide better details.
     
  5. PatFJ40

    PatFJ40

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    JB is on the right track. Check to make sure your sending unit is grounded. How many wires are going to the unit? If there is only one you can stick it straight to a ground point and your gauge should peg all the way over. If it does your wiring and gauge are ok. Let us know what you find.
     
  6. dgangle

    dgangle total rice SILVER Star

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    Last edited: Aug 27, 2009
  7. tkerkela

    tkerkela

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    There are two wires to the fuel cell sender. One ground and one positive. I think the problem might be the ohms. There is a GM sender in it that goes from 0 to 90 ohms and the FJ40 senders are way less than it i found out. I might just try to put a FJ40 sender in the tank and see if it works. Any other help is appreciated.
     
  8. crushr

    crushr

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    The ohm range must match between the sender and the guage. The factory FJ40 fuel gauge uses an unusual ohm range, which no aftermarket senders match. Use an OEM sender or replace the gauge with an aftermarket which matches your sender.
     
  9. dgangle

    dgangle total rice SILVER Star

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    the last post is right on the money.

    I did confirm the sending unit resistance reading on the link I posted above are correct per page 12-27 of the FSM. Gauge diagnostics is covered on page 12-26.

    BEWARE of using the info from Cool Cruisers as it is WRONG. They appeared to only state the acceptable range in variance of the readings, not the true ohm measurements. Short of pulling my sending unit and actually measuring, I'd bet money on the FSM info anyday.

    Per http://coolfj40.stores.yahoo.net/gastanfj19th.html

    "The fuel tank sending units range is from 2.1 ohms to 6.5 ohms. Tank Full 2.1 ohms. Tank 1/2 Full 4.5 ohms. Tank Empty 6.5 ohms"
     
    Last edited: Aug 27, 2009
  10. cruzerman350

    cruzerman350

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    that cool cruisers website is correct. above where you found that it says "# FYI: Float Position Reisistance is as follows:
    # Full -- 17+/- 2.1 Ohms
    # 1/2 -- 45+/- 4.5 Ohms
    # Empty -- 120+/-6.5 Ohms
     
  11. dgangle

    dgangle total rice SILVER Star

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    The website info has been corrected. I sent them an email pointing this out to which they replied thank you.
     
  12. middlecalf

    middlecalf

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    Is there an aftermarket fuel gauge that will fit the form factor of the FJ40 gauge panel, per chance? I'm getting tired of adding gauges all over the place plus running out of room - right now the only gauge in my original cluster I have working is the ammeter (still trying to figure out why the new speedo cable doesn't work).
     
  13. dgangle

    dgangle total rice SILVER Star

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    I am unaware of anyone that has put an aftermarket gas gauge in the stock cluster. There was a reccent thread about mounting small aftermarket gauges into the stock cluster but the person reused the OE gas gauge. There are also plenty of people who have put entire different clusters in that utilize all aftermarket gauges. The current ROTW has done this IIRC.
     
    Last edited: Sep 21, 2009
  14. middlecalf

    middlecalf

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    I saw the thread about upgrade kit for mounting aftermarket gauges, pretty darn cool. But like you said, the fuel gauge remained stock. So here's another question, I know my stock fuel gauge "works" (it climbs to full when shorted across the battery). Has anyone found an aftermarket sender that works with the original (early FJ) fuel gauge?
     
  15. dgangle

    dgangle total rice SILVER Star

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    No. Our's use a range that has been said to be unique.

    Most any fuel guage is only an approximation of the liquid level, especially in something +35 years old. With my poly tank full and stock sending unit, I can drive 75 miles B4 the needle moves off "F". Another 50 and it is on "E". I accept it 4 what it is and am glad it works at all, albeit inaccurate.
     
  16. Downey

    Downey SILVER Star

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    Your 1976 uses a 120 ohm empty, 17 ohm full sending unit. If you can not find one for your aftermarket tank, I can help---PM me.
     

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