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NO tach after Petronix hooked up

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VelodromeRacer

VelodromeRacer

Jedi Trainee
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I need some help here.
I have a 1966 BJ8, and I now have the Petronix pointless
ignition system. My problem, is now my Tach is not working.
The gauge is fine, and according to the wiring diagram, it is hooked up fine. I am sure that I have messed up something with the wiring or coil? Any suggestions or help where I should check?
 
Does your gauge have the inductive loop on the back? These gauges are wired in series with power to the coil and will have RVI written somewhere on their face. If your tach is an RVI type it is time to start looking for an RVC type to replace it or go back to points. Getting an RVI, current sensing, tach to work with electronic ignitions is a hit-or-miss affair.
 
Well Race, You might do this;in some cases the pickup off the white wire loop is inadequate to trigger the Tach.For these cases adding an additional turn to the pickup loop in the back may get you going.---Fwiw-Keoke
 
To get mine to work, I had to put an additional loop (albeit with smaller guage wire) in the pick up at the back of the tach. Pertronix actually told me to eliminate a loop and just have the wire pass through the pick up, but that didn't work for me. That being said, the tach works up to about 3750 rpm's and then drops off beyond that point.
 
I installed a Pertronix a year ago. My tach read too high before hooking the Pertronix up, and still reads too high now, maybe even a little higher than before. I've been hesitant to do anything at all for fear that it might stop working altogether after reading stories like the one above. ??
 
If originality isn't 100% important to you, look on ebay for a comparable RVC series tach and transplant its circuit board behind the RVI face. The RVC tachs are voltage sensing and easier to get to work. Many of them have calibration pots inside so once you do the transplant you can make it accurate (more or less). However, you will only need one wire hooked up to the coil.

My hat is off to those of you lucky enough to get your RVI tachs to work with electronic ignitions. As I mentioned, it's a hit-or-miss thing for them to work and even more rare when you find tweaks that improve their performance.
 
Hi VelodromeRacer, is your car positive or negative ground? Did you convert it when you installed Petronix? I converted mine to negative ground, installed Petronix, converted tach per instructions posted here but it was still goofy, fixed it with replacement of the .22uF capacitor that I got from Radio Shack. Do a search here for BJ8 tach there is lots of good info! Is your tach completely motionless or just reading inaccurately? I assume your tach was fine before Petronix? Let us know! Good luck !! /ubbthreads/images/graemlins/cheers.gif
 
Thanks for the advice, It has the loops, so I may play with that awhile first before I search for the RVC type.

I now know the underside of my dash like never before!
 
While you're on your back looking up, contorted and aching...
I've found it so much easier to wear a little battery operated camper's light that stays on my forehead with a headband. The light always shines where you're looking.
Makes the job a little more comfortable.
 
I should have posted this earlier.
See:
https://members.shaw.ca/tsmit/tachmod/tachmod0.html

Theo Smit has developed a replacement driver board for Smiths tachometer movements. He has taken a dual-approach in his design. With his board you can elect to run the tach as either voltage (RVC) or current (RVI) sensing. This would allow you to leave your existing instrument intact.

I've exchanged emails with him in the past and he commented that the added capacitor fix has mixed results and in some cases temporary.

I'm sure you'll get it to work one way or another but if you want it reliable and accurate you are looking at a circuit transplant of some time.
 
What a cool web page! I told you we were obsessive...who else would do this for a few thousand 40-year old cars??? (I can't wait to order one of those boards.)
 
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