I've got a '87 TurboII in a car thats not a RX7. The car has a vintage VDO tach that worked with the VW and Corvair engines that were in the car from 1978-2002. I can't get the tach to work. I'm using the wire off of the stock trailing coil and am getting a signal that increases with RPMs. The tach is 12volts and has power. Anyone run across this before? Do I need to run something inline to alter the signal? I've tried changing the dial in the back of the tach from 2,4,6 and 8 cyl and still nothing.

 

wire the tach out lead to the primary coil ignitor if using the turbo 2 coil and not the trailing. set the tach to 4 cylender and you should have no problem.

 

[quote name='wdwflash' date='Jul 17 2005, 06:11 AM']I've got a '87 TurboII in a car thats not a RX7. The car has a vintage VDO tach that worked with the VW and Corvair engines that were in the car from 1978-2002. I can't get the tach to work. I'm using the wire off of the stock trailing coil and am getting a signal that increases with RPMs. The tach is 12volts and has power. Anyone run across this before? Do I need to run something inline to alter the signal? I've tried changing the dial in the back of the tach from 2,4,6 and 8 cyl and still nothing.


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I don't exactly understand your problem.



You state you get an increasing signal with RPM's, but the tach doesn't work?



The tach isn't accurate?



The tach needle doesn't move?



How did you confirm the signal was increasing with RPM's?



The trailings coils spit out a "V8" signal.

The leadings spit out a 4-cylinder signal.





-Ted

http://fc3spro.com/

 

The tach worked with two other engines. A 6 cyl turbo Corvair (1964) and a 4cyl VW (1974). I used a digital multi-meter to observe the signal increase from the wire from the trailing coil when rpms are raised. I will try using the lead coil.

 

Okay, I understand now.



The FC spits out a ground "pulse" IIRC, so I hope the aftermarket tach can accept such a signal?





-Ted

http://fc3spro.com/

 

Could you explain "splits out a ground pulse IIRC." I don't quite understand, as to me a ground pulse is one that is already making a circuit. I've tried to find a site for VDO guage questions, but have not been able to find one.



On the leading coil, which lead should I attach to (color, etc)

 

"Ground pulse" is like how it sounds.

Most people can understand a normal (power) pulse, which voltages goes up.



Ground pulse "goes to zero" or ground.

It's also called a "pull to ground" (pulse).



If you try and measure voltage of such a signal, you will not see anything - maybe a minor fluctuation in the voltage reading.

If you measure the pulse while connected to a power (contant +12VDC), you'll see the pulse.





-Ted

http://fc3spro.com/