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Tach adapting for V8

Discussion in '60-Series Wagons' started by Waggoner5, Aug 18, 2004.

  1. Waggoner5

    Waggoner5 SILVER Star

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    I noticed a lot of people are looking for the potentiometer value for making the 6cyl FJ60-62 tach work on a V8. Here is a picture of the install. The pot value is 200ohm. You only use 2 out of 3 lugs. The outer as you maybe can't see, is not used. Attach an aftermarket tach and calibrate yours as needed.
    Gary
    P1010012.JPG
     
    Last edited: Dec 28, 2007
  2. cahilc

    cahilc

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    hijack - but relevant to tachs ...

    While we're talking about tachs ... Doesn't the tach run off of the coil ? If so, wouldn't it be possible to rig a hidden anti-theft 'kill switch' from the tach by taking it to ground, thus grounding out the coil and stopping the truck from starting ?

    Real curious, been chewing on this idea for a while,

    Thanks in advance,
    Cahil
     
  3. Tinker

    Tinker

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    Why do you want a 4K tach on a engine that turns over 5K?. I'm trying to adapt a cheap Auto Meter 6K tach to my 84 FJ60 5.7 Vortec/4l60E - looks like it'll fit (just got info from Painless on the correct harness wire).
     
  4. woody

    woody unhelpful spotter Staff Member Admin

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    adapting is nice for the clean-stock look, and honestly, I can't recall the last time I took my 350 up to 5k....

    Does the AM tach drop in the "stock" spot? pop up pics and info, would like to see that one too!!

    Options are always good....
     
  5. Waggoner5

    Waggoner5 SILVER Star

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    Other than maybe climbing a dune, when would you see over 4-5k RPM? My truck will break major parts at 5k. Come to think of it, my truck will break everything under it, at 5k.

    Woody, the tach rests where it should and is correct all the way to 5k. Its an option for someone who doesn't want to spend even cheap $ on an aftermarket tach. This mod costs 2.79, and fits.
     
  6. DirtyLittleSecret

    DirtyLittleSecret

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    ...and where might one get the "fancy" little 200 ohm potentiometer you have there?
    NAPA - nope
    Radio Shack - nope
    REM - sold out
     
  7. Waggoner5

    Waggoner5 SILVER Star

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    I bought some at Allied electronics. They are a chain, but not sure in your area.
     
  8. ad20k

    ad20k

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    might try www.digikey.com. I think there is a $25 min order.
     
  9. DirtyLittleSecret

    DirtyLittleSecret

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    $25, would buy about 25,000 of these lil' buggers...
    I guess I'm kinda confused as to why a potentiometer rather than just a regular 200 ohm resistor? I mean, there's no reason to adjust it is there?:confused:

    Ah, I see...You're using the aftermarket tach as well to calibrate it and get "visually close".
     
  10. rover67

    rover67 SILVER Star

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    i rev mine up to 6k almost weekly.. sometimes daily.

    I originally did the potentiometer thing too after i did my swap, but ended up doing the 6k rpm autometer tach install.

    but yeah, that motor reallys like it up in the revs... especially when i'm passing an fj cruiser headed up to the slopes :)
     
    Last edited: Dec 5, 2010
  11. DirtyLittleSecret

    DirtyLittleSecret

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    Hey now, I sold a new FJ Cruiser, and stepped up to my FJ62. Pretty soon it'll be an even better move.
     
  12. Dirty Toad

    Dirty Toad

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    Where did you put the new Tach? Got pics of it?
     
  13. rover67

    rover67 SILVER Star

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  14. exrsa1

    exrsa1

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  15. rover67

    rover67 SILVER Star

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    yes, used the stock harness off of the old tach on the back of the autometer. remember to hook the dash dimmer wire back up so the light dims with the others. under the hood the original coil negative wire is wired to the tach signal out on the ECU. This way the AC control also gets the signal.
     
  16. rover67

    rover67 SILVER Star

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  17. FJ60 Dude

    FJ60 Dude

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    so to bring this thread back up....

    i just tried doing this tonight just using 2 100 ohm resistors which should be right where it needs to be and it didn't work.

    i wired it in two diff ways just cause i wasn't sure. maybe somebody can tell me how to wire it in to make it work.....

    [​IMG]

    [​IMG]

    first attempt was inline

    [​IMG]

    then i tried across the terminals....

    [​IMG]
     
  18. ntsqd

    ntsqd technerd

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    The way that I read the OP is that the potentiometer has a max resistance of 200k ohms. What is needed is something less than that and tuning of the resistance is done to calibrate the tach to read correctly.

    If 200k ohms was the exactly correct resistance then soldering the resistors in series would be the correct method.
     
  19. goose4433

    goose4433 SILVER Star

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    I know this thread is a million years old but since it's in the FAQ I thought I would add some detail. I just upgraded my stock tach to work with the SBC 350. A few clarifying details, I put the potentiometer inline with the red wire as the very first post says (unlike the link above which is across terminals). Also, I used a 100k 28 turn pot. Even this seemed like it was too much resistance (perhaps OP was correct when he said 200 ohms?).

    The key to getting this correct is a many turn pot. The tunability is pretty important. If I was doing this again I would experiment with a much smaller resistance potentiometer with many turns.

    I also found an image online of a 6k fj60 colors tach and printed it out. And don't snap the needle like I did!

    IMG_9499.jpg IMG_9500.jpg IMG_9516.jpg