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CDI500R Tacho Output Erratic Reading

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  • CDI500R Tacho Output Erratic Reading

    Over the past few months, I have been seeing an issue with the data log for engine rpm.

    Racepak engine rpm displays a very erratic reading once it passes approximately 7800rpm.

    The issue only seems present at the Racepak though which uses the tacho signal output from the CDI.

    As you can see from the attached, the engine/car itself does not show any signs of issues as the SM4 log is normal, but the same run on the Racepak has the issue.

    The problem has only shown up once we have started turning the engine a bit harder. As the other attached log shows the rpm correctly at 7700rpm but erratic over 7800rpm on the same run.

    It has also always been very erratic on the 2-step since the logger was installed compared to the ecu, but I just assumed this was how it sampled the rpm. But now I am thinking there has always been some problem evident?

    I have spoken to Racepak and they agree with what the data suggests, that there is an issue present with the CDI tacho output?

    Has anyone else seen any similar issues or can suggest where else to look?