z240 Posted October 7, 2011 Share Posted October 7, 2011 I feel bad posting this, its such a simple problem, but I'm done beating my head against the wall on this and have now come to the collective for some ideas on what to do or look for next. Issue. "Routine" complete 83 ZXT turbo engine / harness/ ECU swap into a stock 76 280z chassis. The total job went very smooth. Not my first one. Harness mods are now straight forward, car started on first crank. Runs great. So what's the problem? The tach doesn't work. Searches here reveal no one having any issue with a 280 tach with ZXT ignition. Shouldn't be, same triggering as stock. I am usign the full coil/ignitor from the ZXT. Tests done so far. 1. Confirmation of wiring continuity between the negative side of the coil to the in-line resistor under the pass. dash, then from the inline resistor to the back of the tach bullet connector. Using stock wiring from coil to tach. 2. In-line resistor is correct 2200 ohm value. 3. Confirmation of 12v and ground to correct terminals on back of tach. With key "on" AND with car running. Even tried grounding the tach case with it dangling from the dash. 4. Tach was working correctly with prior stock ignition. 5. All connections clean and tight. 6. Last resort (you'll be proud) was to swap out the tach for a spare. Same issue. Tried yet another spare. Same issue. Not even a bounce or hint that its working. About the only unusual part of this is that we switched the dash location of the Tach and Speedo. I'm thinking this has upset Datsun karma in some way and its not allowing the tach to work when its in such a "wrong" location.... Clearly the only "difference" old to new is the new ZXT coil and the tach wiring running from the dash harness to a different tach physical location. Has anyone else had tach issues with the ZXT coil triggering that I just haven't found in my search? Bigger in-line resistor? Need to use the MSD tach trigger module? I haven't had to do that in the past. Ideas? Hint? Total way out brain waves? Anyone??? Jim Quote Link to comment Share on other sites More sharing options...
FricFrac Posted October 14, 2011 Share Posted October 14, 2011 (edited) Are you trying to trigger your current sensing tach (stock on the earlier S30) with a voltage sensing tach output (S130)? This is how I got mine working on my 240Z with a MSD 6AL 6AL manual - info is on page 8 not 10.... Edited October 14, 2011 by FricFrac Quote Link to comment Share on other sites More sharing options...
z240 Posted October 14, 2011 Author Share Posted October 14, 2011 nope, stock 1976 280z voltage sensing tach. Thanks for giving it some thought. Jim Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 14, 2011 Share Posted October 14, 2011 Have you made any attempt to see if there is a signal in the trigger wire at the tach? You should be able to measure a voltage there when the engine is running. Or, assuming this won't damage the ignition, ground it to see if it kills the eninge. If you have a signal the tach is bad or you missed a wiring problem in the power circuit. Quote Link to comment Share on other sites More sharing options...
z240 Posted October 14, 2011 Author Share Posted October 14, 2011 beerman Actually hadn't thought of that. I assumed that having 0 ohm continuity between the coil and the tach connection wiring would transmit whatever signal there might be, but you're right. Don't know unless you look. I really need to get one of those oscilliscope hookup adapters for my laptop and look at the actiual waveform. The other thing I haven't looked as the quality of the crimp of the wire to the bullet connector on the tach signal wire. Maybe it connects with a meter probe stuck in there, but not when you actually push the bullet on the tach pin. Whose had that problem with the starter "trigger" spade connector ? I know I have.... This guy has had his dash out and in several times in the past... Another thing to do would be to hook up a spare tach in the engine bay with new 3 independant wires to coil -, thru a 2.2k resistor, and +12 and ground and see if it works out there. That would eliminate the car wiring entirely. Might be very instructive. See? It just took some ideas swirling around to get new troubleshooting ideas flowing. Thanks everyone! Jim Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted October 14, 2011 Share Posted October 14, 2011 It sounds like you are on the right track. I'm afraid I can't help further except to say I used to have the same setup, '78 S30 with 280ZXT ignition and the tach worked just fine. Quote Link to comment Share on other sites More sharing options...
cgsheen Posted October 14, 2011 Share Posted October 14, 2011 When we turbo swapped my Son's '76 280 I used the existing wiring to connect the Tach. Can't remember if we pulled his transistor ignition module from under the dash though... The Tach signal wiring has a connection to it. His Tach worked fine for over 4 years then turned flakey just a few weeks ago. We abandoned the existing Tach feed and ran a new wire straight from the coil to the resistor. His Tach is back to working correctly. (I regretted using the existing harness shortly after I did it, but never changed it until now...) On my 260, I ran it that way from the start and have never had any trouble. Wirng the swap on the 260, I used all of the 280ZXT donor wiring I could, ran new where needed, and abandoned as much of the stock wiring as possible. Quote Link to comment Share on other sites More sharing options...
VKLR Posted October 14, 2011 Share Posted October 14, 2011 "Another thing to do would be to hook up a spare tach in the engine bay with new 3 independant wires to coil -, thru a 2.2k resistor, and +12 and ground and see if it works out there. That would eliminate the car wiring entirely. Might be very instructive." You have done everything else, this should tell you something. On another Tach subject. Anyone on here ever try to get the stock 75-78 Tach to work on a Sr20 swap? I'm thinking a MSD DIS Tach adaptor and maybe calibrate the Tach? Let us know what you find. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 15, 2011 Share Posted October 15, 2011 Not sure if it matters but is the coil the same resistance as the prior coil that ran the tach well? Quote Link to comment Share on other sites More sharing options...
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