Tach

Discussion in 'New Hemi Engine Swaps' started by Mopar Sam, Jul 12, 2018.

  1. Mopar Sam

    Mopar Sam Well-Known Member

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    I put a stroked 5.7 in my wife's satellite [sorry,not an a body]. I used the tach signal from the MSD Hemi6 to trigger the FAST EZEFI. How do I hook up the tach? Can I trigger it from the same wire without affecting the efi?
     
  2. Steven190

    Steven190 FABO Gold Member FABO Gold Member

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    I am not familiar with this box. I hope that someone can help. Just my thought is that there maybe interference if you connect the two wires. The only thing I have is I used a 6 AL with the Fast and used different wires for the ECU and the tach.
    Good luck on your project.
     
  3. General Disarray

    General Disarray Well-Known Member

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    Why don't you call the FAST or MSD tech support?
     
  4. billccm

    billccm Well-Known Member

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    I would assume both inputs are high impedance, so yes both inputs can share the same signal wire.
     
  5. Mopar Sam

    Mopar Sam Well-Known Member

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    Yeah, I guess that is what I will do.
     
  6. Mopar Sam

    Mopar Sam Well-Known Member

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    I hope you are right. I know the EZEFI is sensitive to electronic noise. I was hoping some one on here had already one this. When I find out for sure I will post.
     
  7. billccm

    billccm Well-Known Member

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    I recently used a oscilloscope to measure the msd tach signal. It's a clean, stable 24% duty cycle square wave. Voltage peak to peak is right with the battery.

    If the signal gets loaded down you could add a 10K pull up resistor, but I doubt you will need it.
     
  8. billccm

    billccm Well-Known Member

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  9. Map63Vette

    Map63Vette Well-Known Member

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    I'm splitting the tach signal to run my Megasquirt and my column mounted tach and haven't had any issue so far. I had originally tried to use the ignition output of my Megasquirt to run it, but it was easier to just use the signal straight from the MSD box.
     
  10. Mopar Sam

    Mopar Sam Well-Known Member

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    Thanks! I think I will try it.
     
  11. Peter Bates

    Peter Bates 1973 Cuda owner for 36yrs

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    If you have a obd port for the computer on your hemi you could buy a Dakota digital interface unit. It has two signals for the tach. That's how I was able to get a clean signal from my CPU to my speed hut tach. Now I just need to get a signal to my tcu tranny controller. I tried to no avail to pull a signal off the motor
     
  12. Mopar Sam

    Mopar Sam Well-Known Member

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    No obd. It is a FASTEZEFI multiport system. I got sidetracked on some other projects and haven't done anything on it yet. I just set her rev limiter to 6500.
     
  13. 408 swinger

    408 swinger FABO Gold Member FABO Gold Member

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    Update?
     
  14. Buschi340

    Buschi340 Well-Known Member

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    so you can use that one Output cable to run for example 2 tachs?
     
  15. Map63Vette

    Map63Vette Well-Known Member

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    As far as I'm aware you can. It's just a square wave signal and it's not meant to carry power, just voltage level. Pretty sure tachs would be high impedance devices that have large input resistance so they don't have a big power draw. I'm sure the output line is limited in what it can supply though, so if you stacked enough things together I could see it potentially being a problem. I don't think you'd have issue running two things though.
     
    • Agree Agree x 1
    • Buschi340

      Buschi340 Well-Known Member

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      will figure that out this winter. just two tachs, not an endless amount of tachs.. :) The one in the dash is hard to read sometimes
       
    • famous bob

      famous bob mopar misfit

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      I DON`T REMEBER OFFHAND , BUT I DIDN`T HOOK BOTH UP TO THE BOX, THINK FAST SAID NOT TO. Call fast and ask for Dave.