09-02-2020, 03:59 AM
tests
see what the PCM tacho pin does naked to scope probe tip. dead nor not.
if dead we add a pull up resistor 1k ohm is good to 12vdc source. (ecu power or ignition on, key on DC power)
if now you get nice 12vdc square wave we look at polarity.
check the if dwell pulse is at the 12 volt end (inverted wrong) or at 0vdc end correctly. as it must be.
if at 12vdc end this dwell pulse we must add 1 more transistor outside ECU on that pin. (1 transistor and 2 resistors ,$1 cost)
this if needed buffer will driver the 97 old tacho great.
last is PRT, pulse repetition time. of the negative pulses seen. we must make this match the 97 tacho to be seen as 1 coil spark engine not 4.
I do not know what your ECU wil do here. for PRT. Ive idea at all what this ECU sends on this pin but is fun to learn. The old tacho needs what a call 4x pulses.
4 spark pulses that charge a capacitor in the Tacho head, very crude but works.
see what the PCM tacho pin does naked to scope probe tip. dead nor not.
if dead we add a pull up resistor 1k ohm is good to 12vdc source. (ecu power or ignition on, key on DC power)
if now you get nice 12vdc square wave we look at polarity.
check the if dwell pulse is at the 12 volt end (inverted wrong) or at 0vdc end correctly. as it must be.
if at 12vdc end this dwell pulse we must add 1 more transistor outside ECU on that pin. (1 transistor and 2 resistors ,$1 cost)
this if needed buffer will driver the 97 old tacho great.
last is PRT, pulse repetition time. of the negative pulses seen. we must make this match the 97 tacho to be seen as 1 coil spark engine not 4.
I do not know what your ECU wil do here. for PRT. Ive idea at all what this ECU sends on this pin but is fun to learn. The old tacho needs what a call 4x pulses.
4 spark pulses that charge a capacitor in the Tacho head, very crude but works.
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