'94 7.3 tachometer

Discussion in '6.9L IH & 7.3L IDI Diesels' started by lkrasner, Oct 18, 2018.

  1. lkrasner

    lkrasner Registered User

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    Simple question: My Short bus E350 with a 7.3 IDI does not have a tach on the dash cluster. I really would like to have one. Does this engine have a tach sensor built in? I assume it must for the E4OD, right? How can I check, and what is the best method for adding a gauge? If it's got any kind of sensor that will give me an analog or pulsed output, I'd be inclined to just build one myself. I'm an electrical engineering student, and I've got plenty of microcontrollers laying around. Counting pulses isn't exactly rocket science, and it seems like every tach kit I've seen is unnecessarily expensive.
     
  2. genscripter

    genscripter Full Access Member

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    Thewespaul likes this.
  3. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    If you have an e40d then you have a tach signal, you just need a cluster that has a tach
     
  4. lkrasner

    lkrasner Registered User

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    Does anyone have technical details on the signal from the tach sensor on the injection pump housing? I am planning to build my own tach using a microcontroller to read the signal. Any data would be useful so I don't have to find a way to get a scope on it to figure it out. I'm guessing it's just a square wave with varying duty cycle or frequency?
     
  5. ifrythings

    ifrythings Full Access Member

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    The signal from the tach sensor is a variable frequency sine wave who’s voltage increases with frequency. The factory tachometer uses a input buffer designed to take the tach signal and convert it to a constant voltage square wave to run into the lm1819 air core meter driver. From there it’s run through a frequency to voltage converter and then turned into a sine and cosine component to driver the meter movement.

    To make a tach for a Microcontroller you’ll need an input buffer as above to give you a 0-5v (or whatever voltage your running your micro at) and then use a capture input to get the frequency (Note: the tach sensor puts out 54 pulses per rev). From there it’s up to you how you want to display it.
     
  6. lkrasner

    lkrasner Registered User

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    Perfect, exactly the info I needed. I'll definitely make a post doccumenting the project when I find time to work on it. Arduino and other hobbyist microcontroller boards have really made this possible for people these days, it's a shame more people aren't embracing the diy aspect more. It's the best way to really learn about how stuff works.
     
  7. ifrythings

    ifrythings Full Access Member

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    The TECA (E4OD computer) will have a tach output but mite not have the wire populated in the vans. The TECA outputs a buffered tach signal that’s around 7v, on mine it was a jacked up looking signal that floated above ground with a large over shoot on the rising edge. It is still a 54 pulse per rev output just like the tach sensor is.

    I’m using PIC for my projects mostly because I had some chips and a programmer and dev board before the Arduino came out.
     

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