New Engine. Tach doesn't work.

[viejopatron]

I’ve read many of the postings here regarding tachometer compatibility with different ignitions and it’s still a mystery to me.

I installed a 3,0 in my ‘71T and retained the original CDS. I DID install a Petronix Ignitor sensor in the Bosch distributor and a DIY engine harness.



Of course, I have NO response from the Tachometer.

To me, its seems that if the CDS is original and its interface with the car is unchanged and the engine runs, why wouldn’t the tach function?

I measured the RPM sensor resistances; both were within specification ranges.

I connected my DMM to Terminal D on CD Box. I first checked voltage; it’s proportional with engine speed. Max voltage seen was approximately 2 VDC @ approximately 2000 rpm. I switched the meter to read Hertz; again got a proportional value with engine speed. Max frequency seen was approximately 100 Hz @ approximately 2000 rpm. OK I thought, its proportional and not scary voltage.

I made 3 separate hookups of open connectors to Terminal D. 2 on the chassis harness and 1 on the engine harness. No reaction at Tach. The only reaction I see is when engine is turned off; needle moves off zero then resettles.



Any suggestions?

[Lukesportsman]

Question though is the signal/voltage from the ignitor similar or near as high as it was from the points? Some of the early tach's require as much as 150v to fire. In ugrading the tach, it may have caused you more headaches than the whole engine swap.

[gamin]

Bob Ashlock, a fellow pelican, makes a tach adapter that probably will work for you. I am using a later model tach in my 70 and Bob's adapter made it work. Find him at ashlocktech.com or use his email ratech@pacbell.net.

[BURN-BROS]

Gary,

What type of distributor did you use???