TrumpetRhapsody Posted July 21, 2009 Share Posted July 21, 2009 I'm attempting to use this circuit to drive my stock 260z tachometer: I'm 80% sure I've hooked everything up right, but the tach does nothing. I've tried it with and without the stock resistor inline, with no effect. My next course of action is to pull the tach and make sure it's getting the signal, and try substituting it with a spare from a 280z. Has anyone used this circuit successfully? Quote Link to comment Share on other sites More sharing options...
1 fast z Posted July 21, 2009 Share Posted July 21, 2009 I believe the 240's ran off of the positive side of the coil and not the negative, not sure if the 260 was this way or not. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 Well my wiring harness showed the blue wire I tapped into going to the negative side of the coil, so I don't think that's the problem. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 Try connecting the tach wire directly to ONE COIL (-) wire on one of the coils in the pack to see if the tach is actually working like it used to before EDIS. No diodes, no nothing, straight to one of the (-) wires on one coil pack coils. Sure it will read 1/3 what it should but all you want to do is test that the tach and wiring is all OK before proceeding. Once you confirm that it works just like any other tach connected directly to a single coil, then try installing a 1N4004DICT-ND diode on that same one wire. If it still works, then you added the diode correctly. If it works with one wire and one diode, then try adding a second wire/diode connection to a second coil and splice that into what was working before and see if it still works as a pair. If that works, add the third. You should see the tach read 1/3 more RPM's with each wire addition. Only if the signal gets a bit wiggy do you need to try the 1N4746ADICT-ND between the tach and other diodes. I did not need it. As long as you work through it one piece at a time then you can see what works and where a problem starts. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 So you did get it working with this circuit, minus the 1N4746? Were you running the resistor inline to the tach? What year tach were you using? I'll try all that and see if it makes a difference, thanks. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 I had a 280Z tach and inline resistor in the 260Z. I'm not sure what month your 260Z was made or what tach is really in it. What made it work with EDIS (for me) was removing the inline resistor and using only the diodes that touched the coil wires on the coil pack. It does not matter, just follow the procedure of ONE connection at a time(just wire wrap). It took me about a half an hour to find a combination that worked. When it all works you can solder the connections and wrap it up.... Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 Alright, progress. With the tach only connected to one coil (with or without resistor, with or without diode) it gets the 1/3 signal. As soon as I add a second coil, the tach goes dead. This is all without the Zener diode, adding it makes no difference. Is there a way to add a capacitor to triple the signal, and just use one coil? Not sure if that would work or not, I'm no EE Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 OK, that's a start. Try a different diode. I had the EXACT same thing happen and it was a bad diode... Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 Nope, tried different diodes and tried rotating combo's of which coils I was combining. It made no difference, as soon as I add a second coil the tach dies. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 as soon as I add a second coil the tach dies. That should not happen. Each single coil is no different than any other coil. Ganging them together just provides more pulses. Only thing I can think of is that the electrical pulse from the one coil is being grounded out when you added the second connection (so it stops being seen by the tach). That to me suggests that the diodes are not doing a good job of preventing current flowing to the other coil wire grounds. Edit: One cute problem could be that the original 1st diode you installed and saw te tach work 1/3 was actually bad. Adding more good ones all ground out through that original bad one "that was working ".... Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 Hmm, that seems like a possiblity. Wouldn't that affect the running condition of the car itself though? Is there any way to test for this condition? Maybe I need... stronger diodes? Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 Hmm, that seems like a possiblity. Wouldn't that affect the running condition of the car itself though? Is there any way to test for this condition? Maybe I need... stronger diodes? The pulse is awfully weak and is positive. I'll make a guess and say that a weak + pulse is not going to make the other coils fire off (since they fire by grounding) so the engine will still run fine. I was lucky enough to order 6 diodes (1N4004DICT-ND) from DigiKey and kept working with them to find something that worked right. First error I made was probably hitting them with a lot of heat when i soldered them all up BEFORE ever testing them. Live & learn.... Good luck with it! Sounds like you're real close. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 21, 2009 Author Share Posted July 21, 2009 Radioshack has them for 99c for two, so when I get a chance I guess I'll give this another go. I give up for now lol. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted July 21, 2009 Share Posted July 21, 2009 Radioshack has them for 99c for two, so when I get a chance I guess I'll give this another go. I give up for now lol. ...Or just multiply what the tach reads by 3x Yea, I never thought I would have trouble with what looks to be a simple circuit after doing an entire MSII + EDIS conversion. This little bit was supposed to be easy and turned out to be more of a trial-and-error to get it to work right! Ahhhh! Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted July 21, 2009 Share Posted July 21, 2009 Haha I told him to do that when I went over for lunch today Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted July 30, 2009 Share Posted July 30, 2009 Open up your tach, and bypass the large resistor that is connected to the "coil input". You can follow from the connection to the circuit board and will be the first resistor in line with it. I did this on mine to get my 280Z tach to work with my GM DIS ignition. If you do a search there is a thread with pictures showing the resitor to bypass. Just as a note, my tach stops reading at high RPM, some information I've read suggests that above 6200 RPM, the dwell is too short for the tach to read correctly, and so it stops reading. I don't spend much time above 6200 RPM, since my rev limiter is set around 6400 RPM, but I do see my tach drop frequently. LOL Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted July 30, 2009 Author Share Posted July 30, 2009 Hmm interesting idea, thanks for the suggestion! I'll search around for that method. Now to figure out how to get the tach out past my full dash cap Quote Link to comment Share on other sites More sharing options...
Xnke Posted August 3, 2009 Share Posted August 3, 2009 Don't bother with the silly diode trick If you have a 240Z style tachometer, there are much easier ways to run a current-triggered tach. Easiest way to run a current triggered tach (this is 240Z and early 260Z) is to run it just like it was originally: power the coils THROUGH the tach, i.e. put the tach in series with the power to the coil pack. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted August 3, 2009 Author Share Posted August 3, 2009 First off I have a Late 260z, which if the wiring diagram was correct triggers off the negative side of the coil. Second, I don't believe the positive signal to the EDIS coil packs is switched, so I don't know that would provide a tach signal. If I can figure out how to get the tach out the back of the dash, or pull the dash entirely, I'll try that. Quote Link to comment Share on other sites More sharing options...
Xnke Posted August 3, 2009 Share Posted August 3, 2009 Sorry-I thought we were speaking of the early 260Z/240Z tach. Which, if you put the tach and coil power in series, works fine, as that is how the tach was wired from the factory. Now, for a 280Z tach, you are right, the multiple diodes off the coils normally works. Have you tried using the edis tach output or the MS tach output? Quote Link to comment Share on other sites More sharing options...
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