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Thread: E67 tach output settings

  1. #1
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    E67 tach output settings

    ECU is detected as E67 GM LS3 480 crate motor. Current under the engine tab
    I have the following options.
    Type: Serial / crank / frequency
    factory setting = frequency
    high and low values = 15

    I have changed the value from 15 to 7 but the tach still reads the same 1/2 of the original engine RPM.

    What are the different settings and how do they effect the tach output.

    Setting the type to crank = 0 tach reading

    Setting the type to frequency and setting to any value, always the tach reads 1/2 of actual.

    So Serial / Crank / Frequency what is the output signal produced. If I had an oscilloscope I would know why I dont get the expected result. Anyone know what these settings do ?

    I am already using the suggested connection (pull up resistor) to make a tach work, just it reads 1/2 of the actual RPM.

    Using the factory tach in my 1978 corvette.

  2. #2
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    Quote Originally Posted by ls378corvette View Post
    ECU is detected as E67 GM LS3 480 crate motor. Current under the engine tab
    I have the following options.
    Type: Serial / crank / frequency
    factory setting = frequency
    high and low values = 15

    I have changed the value from 15 to 7 but the tach still reads the same 1/2 of the original engine RPM.

    What are the different settings and how do they effect the tach output.

    Setting the type to crank = 0 tach reading

    Setting the type to frequency and setting to any value, always the tach reads 1/2 of actual.

    So Serial / Crank / Frequency what is the output signal produced. If I had an oscilloscope I would know why I dont get the expected result. Anyone know what these settings do ?

    I am already using the suggested connection (pull up resistor) to make a tach work, just it reads 1/2 of the actual RPM.

    Using the factory tach in my 1978 corvette.

    So I connected an oscilloscope to the ECM Tach output and found changing the setting from Frequency to Crank changed the signal from a PWM signal to a constant voltage ( no signal ) this doesn't sound correct unless the
    change puts the output signal on a different pin ?

    Anyone have any idea's on what to do next ?

  3. #3
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    Sep 2021
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    I?m having the same exact issue. I have an LS3/480 with e67 put in a 1994 Blazer. I will still be digging on this one. Thanks for explaining the issues you are having.

  4. #4
    Tuning Addict blindsquirrel's Avatar
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    A lot of the GMPP ECMs have secret, hidden limitations on inputs/outputs that you will only know about because you make a change to something and it works exactly the same as it did before. The min/max values shown in the editor do not accurately reflect what the ECM hardware is capable of doing, it seems those descriptions are just carried over from the regular production E67s.