 Tacho test for output from Permatune CDI ?, any way to test with multimeter for a pulse ?. |
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| porschetub |
 Sep 27 2022, 03:57 PM
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Advanced Member  Group: Members Posts: 4,728 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None  |
Have issue with 2 tach's not working and after testing all connections @ tach and Tach-adapt I'am left with the black/purple wire from the CDI (3 pin) to test.
My later tach (low voltage ) will cause the Tach-adapt LED to come on with the ignition on and the needle bounces when cranking however with engine running ...nothing. My early tach (high voltage) isn't working and this is the one I will convert to Ashlock-tech circuit board replacement but need to know the pulse from CDI is working. TIA,cheers. |
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| Spoke |
Sep 27 2022, 04:01 PM
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Jerry Group: Members Posts: 7,079 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None 
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Most likely the answer is no. Multimeters are good for resistance, DC voltages, and AC sinusoidal voltages but not pulses. You'll need an oscilloscope.
Small oscilloscopes are not out of reason WRT price. Here's one for less than $50: Oscilloscope for $47 I'm having issues with my 911 and getting ready to test the Permatune CDI with my oscilloscope. |
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| porschetub |
Sep 27 2022, 04:59 PM
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#3
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Advanced Member Group: Members Posts: 4,728 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(Spoke @ Sep 28 2022, 10:01 AM)  Most likely the answer is no. Multimeters are good for resistance, DC voltages, and AC sinusoidal voltages but not pulses. You'll need an oscilloscope. Small oscilloscopes are not out of reason WRT price. Here's one for less than $50: Oscilloscope for $47 I'm having issues with my 911 and getting ready to test the Permatune CDI with my oscilloscope. Thanks kinda had a feeling that was the answer from someone of your skills would provide so thanks heaps,will order the upgrade circuit board for the silver dot tach and go from there cheers. |
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| Retroracer |
Sep 27 2022, 07:18 PM
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#4
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Senior Member Group: Members Posts: 620 Joined: 7-July 13 From: Bend OR Member No.: 16,100 Region Association: Pacific Northwest
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Agree that a 'scope is best for debug of the CDI tach pulses. An alternate might be:
battery powered scope a little funky to control, but is battery powered, so one less cable to trail over the car. With the motor idling at 1000rpm, you should see pulses repeating at a 50Hz rate. - Tony |
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