lowrider Posted March 10, 2011 Share Posted March 10, 2011 (edited) Just dug my tach out the back of the dash (that was quite the experience), and did the resistor bridging mod. While the signal is somewhat stronger when I pinch the wires together, directly connected it's still not working. When I get home tonight I'm going to re-do all my diodes and try one last time, just in case I overheated one while soldering. At that point if it still doesn't work I'm just going to give up and order an autometer tach. Stupid 260z's. I had the same problem when I was hooking my tach up. It would respond when I bridged them with my finger. My memory is completely shot, and I dont remember all of the details of how I made it work. I did however follow the instructions in the mega manual, for the exception of the zener diode. Radioshack didn't carry the 16v zener diode that the instructions called for. Instead I used two 1N4742A zener diodes inline after the merge of the three diodes coming off of the coils' negative. Im thinking that I also placed a resistor in the circuit, but I cant remember for sure. I guess I could unwrap my wiring and find out. edit* By no means am I electricaly savy I just started putting stuff together and It worked. How it worked is beyond me! Edited March 10, 2011 by lowrider Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted March 10, 2011 Share Posted March 10, 2011 Hmm I ran into the same issue with finding the 16v zener, i'm also using the 4742A. I'll try running two inline like you did and see what happens real quick. Quote Link to comment Share on other sites More sharing options...
lowrider Posted March 10, 2011 Share Posted March 10, 2011 Hmm I ran into the same issue with finding the 16v zener, i'm also using the 4742A. I'll try running two inline like you did and see what happens real quick. See if that does anything. I will go out into the shop and check and see how I wired everything together. Quote Link to comment Share on other sites More sharing options...
lowrider Posted March 10, 2011 Share Posted March 10, 2011 See if that does anything. I will go out into the shop and check and see how I wired everything together. I just looked, and I infact have the two 1N4742A's, no resistor. My tach is a litte jumpy when it first starts, but reving and holding rpm it's rock steady. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted March 10, 2011 Share Posted March 10, 2011 Wow Ok... time for a slice of humble pie. Apparently two years ago when I was troubleshooting this issue, I soldered everything back together with the Zener diode facing the wrong way (didn't work in either direction though). So what this tells me is that with the proper circuit out of the megamanual (apparently the 12v zener is ok), and by bypassing the internal resistor, this WILL work. My Z is outside running, with the tach reading. I rev'd it out to 6500rpm (or so it said) and it doesn't drop, looks smooth. From here I'll start seeing how accurate it is compared to logs. Thanks for the help everyone. Quote Link to comment Share on other sites More sharing options...
lowrider Posted March 10, 2011 Share Posted March 10, 2011 (edited) Wow Ok... time for a slice of humble pie. Apparently two years ago when I was troubleshooting this issue, I soldered everything back together with the Zener diode facing the wrong way (didn't work in either direction though). So what this tells me is that with the proper circuit out of the megamanual (apparently the 12v zener is ok), and by bypassing the internal resistor, this WILL work. My Z is outside running, with the tach reading. I rev'd it out to 6500rpm (or so it said) and it doesn't drop, looks smooth. From here I'll start seeing how accurate it is compared to logs. Thanks for the help everyone. Great! It's the simple mistakes that always get ya! Im not sure why mine needs the two Zener diodes...But It works so I'm not fooling with it. Edited March 10, 2011 by lowrider Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted December 17, 2012 Share Posted December 17, 2012 Back from the dead. Since I got this working last march, it's slowly gone downhill. The tach started bouncing around once I got to 4k or so, that point shifted around for awhile, and now anywhere from 3k+ just goes nuts. I don't know if those diodes are burning out or what the story is, but i'm going to try for Z-Ya's original circuit. I was going to try the MSextra suggestion, which is like Z-ya's but uses an actual output and a relay coil, but I'd rather venture into charted territory instead. I'll update once I get around to this. Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 18, 2012 Author Share Posted December 18, 2012 The signal going to the tach is inverted. Are you sure you have the diodes connected correctly? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.