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How To: Fix erratic fuel level reading on digital dash

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  • #16
    Fairly certain that the silver box is to convert the analog sender signal to the digital dash signal. The analog sender pic from courtesy does not have the silver box, and the digital one does and looks just like the same sender with the silver box.
    88SS - #300 - http://z31performance.com/showthread.php?18360

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    • #17
      I had a question thats a little off topic for this thread but not to far. I have a 84 50 AE and the gas gauge just doesn't come on to begin with. the rest of my digital dash works fine except that. I don't know how much I get to a gallon so I have to just fill it up like every week or so just to make sure. If anyones got a option for this that would be great. its my first Z.

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      • #18
        Yea Pepper is probably right, I ripped apart plenty of z31's, 86na digidash, 87na/87t analog etc and never saw that silver box

        Safe guess to assume nissan ran out of one kind of sender and made a patch kit to make it universal

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        • #19
          Unleashed_Z wrote: I had a question thats a little off topic for this thread but not to far. I have a 84 50 AE and the gas gauge just doesn't come on to begin with. the rest of my digital dash works fine except that. I don't know how much I get to a gallon so I have to just fill it up like every week or so just to make sure. If anyones got a option for this that would be great. its my first Z.
          Well first off...make sure the connector is plugged in. It's under the carpet in the hatch. (It's the white connector)

          '86 NA2T: Cone filter, 3 in. turbo back, poly engine mounts, stock t3, tokico 5-ways, rattle canned engine bay, etc etc

          "As I lay rubber down the street, I pray for traction I may keep, and if I do begin to slide, please dear God protect my ride! - Amen!!!!"

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          • #20
            For those who owned digital models, has function with and without that silver box been compared? I do not have a silver box in my z.

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            • #21
              Someone please help where can i find the fuel sending unit for the digital dash in a z31 part # 25060-17p75. I am in need of a new one. Please help anyone, thanks!

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              • Dunkine
                Dunkine commented
                Editing a comment
                Look and see if you have a silver box back there. If it's there, I believe you can use the new style analog sender and it converts the single. Not positive on this. I think there's a thread on here about it.

            • #22
              Thanks for the information but yeah I replaced the silver box last week & thought that was the problem so now I need to replace the fuel sending unit (25060 17P75)
              But I can't find it anywhere so your saying this part @ the link below

              https://www.ebay.com/p/Nissan-250601...nit/1322195968

              OR
              ​​
              https://www.courtesyparts.com/oem-pa...nit-2506017p65

              Is that the new unit that will send the signal to the new silver box to cause the digital dash fuel gauge to work properly? Let me know when you can thanks!
              Last edited by BJay314; 04-26-2018, 01:20 AM.

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              • Dunkine
                Dunkine commented
                Editing a comment
                Yeah, the ebay one is the new type sending unit, but it says it won't work with digital dashes. I seem to remember reading that there was a silver box included with the analog sending unit to make it work on digital dashes. Trying to find the thread about it.

              • Dunkine
                Dunkine commented
                Editing a comment
                Some info at the beginning of this thread "The new kit will include the silver box for digital dash cars and includes the integral jumper harness. If your car does not originally have the silver box and the new kit has one, install it as shown in the steps below." But doesn't say if the silver box makes the analog one work.

            • #23
              Looks like you can use updated sending units with the arms instead of the cylinder style if you have the silver box to convert the signal.

              From: https://www.reddit.com/r/300zx/comme...l_adapter_box/

              "Interest in a Replacement Fuel Level Adapter Box? (self.300zx)

              submitted 1 year ago* by dafunkmonster I'm working on creating an aftermarket replacement for Nissan Part Number 25065-17P15. This part is the silver box that you would get if you ordered an updated float-arm fuel level sensor for an 84-89 300ZX GLL.

              The original fuel level senders were cylindrical with a foam float inside that dragged wipers across several linear potentiometer strips which created analog voltage signals which the dash would interpret as fuel levels. There were two versions: one for cars with an analog dash, and one for cars with a digital dash (GLL).

              But this design sucked - the foam float would get saturated and stop floating as well as it used to, and the contacts would get corroded. This would result in unreliable fuel level readings. My own first Z31 would read "E" when it actually had half a tank left.

              So, Nissan created an updated fuel level sender that used a float-arm design instead. It used plastic floats and rotary potentiometers to produce the fuel level signals. However, instead of producing two distinct variants (one for analog dash and one for digital dash), they created one float-arm fuel level sender which worked with analog dash cars, and then created an adapter box that transformed the analog dash signal for use with a digital dash. If you ordered the analog dash part number, you'd get a fuel level sender. If you ordered the digital dash part number, you'd get a fuel level sender and a silver box that plugged in between your sender and the harness.

              Until recently, this adapter box was available directly from Nissan. Unfortunately, it appears that they've exhausted their new old stock of these units, and anyone with a digital dash car who wants to replace their fuel level sender is SOL. The analog fuel level senders are still available, but neither the adapter boxes nor the digital fuel level senders are available. (I couldn't even find new old stock of the original cylinder-style fuel level sender for GLLs.)

              So, being a computer engineer, I set out to figure out how this adapter box works and what the differences are between the analog sender and the digital sender. Long story short, I figured it out. It's actually pretty simple to convert the signals, but your average hobbyist mechanic is probably not equipped to rig up their own solution.

              I'm now working on a design for a replacement adapter box that will allow you to use a brand new analog fuel level sender (still available from Nissan) with your digital dash. It will also perform some filtering to eliminate transient fluctuations in fuel level readings that you'd see from braking or turning (the cylinder-style senders were heavily damped in this regard, but the float-arm senders are not).

              I have a working prototype, and I just need to finish with calibration and testing. After that, I'm going to start working on a PCB layout and an enclosure, etc. and then look into doing a production run of these adapter boxes.

              Before I proceed with that, though, I need to figure out how much demand there is for it, and what people would be willing to pay for one."

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              • BJay314
                BJay314 commented
                Editing a comment
                Because the part is discontinued I think there would be a market for such a product. Has it been completed I would like to purchase one?

            • #24
              So I am willing to purchase one of those do you know if he ever got into production? But okay if I am understanding this correctly the 300zx partsforyou.Com guy Steve sold me a new silver box a couple weeks ago so if I purchase the new analog sending unit 25060 17P65 from eBay & connect it to my new silver box & I should have functioning digital dash fuel meter? Do you think that would work lmk?
              Last edited by BJay314; 04-26-2018, 05:03 PM.

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              • Dunkine
                Dunkine commented
                Editing a comment
                I keep waiting for one of the digi dash guys to chime in... But yeah, that's the purpose of the silver box, to convert the analog senders to work with the digital dash. Yep, ebay, amazon, nissanpartsdeal, local dealership, wherever is cheapest. 84-89 all the same, turbo, non-turbo, doesn't matter.

            • #25
              Okay thanks alot I'm ordering part number 25060 17P65 to work with the new silver box I'll post the results

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              • #26
                just fyi ... I replaced my digi fuel ( 1987 gll turbo ) and got the silver box levels was fine ... then later I upgraded to the tt fuel pump ,... later the gauge failed again .. shows half full on 3/4 tank empty on 1/2 tank
                so I know I need to refocus on it .. but the part is NLA ... Who does any refurbushing on these parts Or can I make it work again myself ?
                ]this is an issue ..

                what is weird my 1985 gl analog gas gauge has always worked no problem ... should I try to get a sender from a pre 86 car ? geez ...
                Last edited by dbruce; 07-11-2018, 02:59 PM.

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                • #27
                  The culprit is the silver box that converts the signal from analog to digital: when that goes bad, it causes issues. That is the part that makes the fuel level sender for digi dash cars NLA.

                  I've had some thoughts on this, but haven't made a move myself since my sending unit currently reads correctly *knocking on wood*. Tri-Starr is a company that rebuilds sending units for several other makes and model cars: they're very popular in the S30 world for rebuilding those NLA sending units. I don't know the extent of their knowledge and ability, but it might be worth it for someone to approach them and see if they might be able to solve this problem.

                  http://tristarrradiator.com/
                  '86 300ZXT GLL
                  '78 Datsun 280Z
                  '04 Saab 9-3 Aero

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                  • #28
                    thanks for this thread ...

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                    • #29
                      My 89t has the old style can and no box. (Digital dash). To get mine working all I had to do was replace the float. The little tabs that ride on the rail for lack of a better word break off on the float. Got a float for a dollar at the JY with perfect tabs, problem solved.
                      Jeff
                      71 240z

                      80 280zx 10th Anniversary

                      88 300zx Turbo, 89 300zx Turbo

                      Datsun Jeff

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                      • #30
                        Dunkine, I'm in need of one as well. I contacted courtesy Nissan couple years ago when they had the part but told me it wasn't the correct part and couldn't say if it would work. I should've taken a chance then. I would be interested in the new unit as well. I still have the original cylinder style tho.
                        Last edited by GS84ae; 08-23-2018, 10:40 AM. Reason: spelling error

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