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Posted by: porschetub Sep 27 2022, 03:57 PM

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.

Posted by: Spoke Sep 27 2022, 04:01 PM

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:

https://www.amazon.com/STARTO-Handheld-Oscilloscope-BNC-Clip-Assembled/dp/B07QL3SS7S/ref=asc_df_B07QL3SS7S?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80745502739822&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584345029413246&psc=1

I'm having issues with my 911 and getting ready to test the Permatune CDI with my oscilloscope.

Posted by: porschetub Sep 27 2022, 04:59 PM

QUOTE(Spoke @ Sep 28 2022, 10:01 AM)

Posted by: Retroracer Sep 27 2022, 07:18 PM

Agree that a 'scope is best for debug of the CDI tach pulses. An alternate might be:

https://www.amazon.com/Oscilloscope-Portable-Handheld-Digital-Storage/dp/B08DG1C129/ref=asc_df_B08DG1C129/?tag=hyprod-20&linkCode=df0&hvadid=475770909319&hvpos=&hvnetw=g&hvrand=14361562252255070849&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033151&hvtargid=pla-1042004121297&psc=1

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