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RPM signal from stand-alone ECU to Stock Tach

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  • RPM signal from stand-alone ECU to Stock Tach

    Hello Team,
    I'm planning out my stand-alone EMS install. I will be running full sequential fuel and spark. I assume that some signal modification is necessary to get from a sequential format to a wasted spark (stock) format. For those of you who are already running sequential, how did you get your tach signal working with the stock tach?

  • #2
    I am using megasquirt for my fuel injection and spark control. I modified my original megasquirt setup to drive the stock tach. I did a write up here. I can't say whether you'll have to build a circuit to condition the tach signal from your ECU like I did.

    I'm not sure if i understand the wasted spark and sequential part of your question. The type of fuel and spark control shouldn't effect the signal your dash tachometer needs or receives. Also, the stock ignition system is distributor not wated spark. The stock tach in the instrument cluster expects a pulsed signal, one pulse per revolution. If you get the pulsed signal in the correct voltage range, it should drive the stock tach fine. Some older systems would drive the tach from the spark signal, but most all of the newer systems use a dedicated RPM signal output from the ECU for the tachometer. The stock tach with the OEM ECU is driven by a dedicated RPM signal from the ECU. I imagine your EMS ECU has an pulsed signal, RPM output you can use to drive the your tach.

    Sorry if I misunderstood part of your post. Good luck with the EMS install.



    • #3
      I use a Vipec V44 in both my race cars, it has a tach output signal line,,, in both cases I took the tach output directly to the tach input and it works perfectly.
      I'm running sequential on spark and fuel on both cars.

      In my Lachsilber club race car I still use a stock E30M3 instrument cluster and its working perfectly with the stock E30M3 tach (and an Automoter shift light wired into that same line).

      On my BTCC car it has the standard issue BMW Motorsport Stack analog tach, same situation. Works perfectly off the Vipec tach output.
      Hope that is helpful.
      jimmy p.
      87 E30 M3 Prodrive British Touring Car
      88 E30 M3 Zinnoberot - Street
      88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
      92 E30 M Technic Cabrio - S14 POWERED!
      98 318Ti M44, Base - Morea Green
      04 Ford F350 - V10


      • #4
        Brad & JP,
        Thanks for the input and my apologies for my poorly worded question. I've done some more research and my standalone can drive the stock tach via a GPIO. At this point I'm just trying to figure out how to physically wire things up using as much of the stock harness as possible. That leads me to my next question...