Metro Posted March 4, 2007 Share Posted March 4, 2007 It's been a while since I've posted, I had to stop messing with the car because I was getting burnt out trying to fix all the various problems.. Anyway, ever since I've started using megasquirt, I've had problems getting the in dash tach in my Z to work correctly. Originally, it would work up until 3500-4000rpms then it would go crazy jumping all around. A few months later it stopped working entirely. Thinking I killed the tach, I bought another one and it didn't work either. So... I must be doing something wrong. My setup: 1976 280z MSnS-extra 29q2 on a v3 board (it's been a while.. I think that's correct) 4pin GM HEI doing spark The tach wire is coming directly to the negative side of the coil going directly to the tach quick connect under the dash. I had tried using the resistor that came with the 280zx turbo, but it doesn't make a difference. I've tried various different sized resistors between the coil negative and the tach and it's all the same - nothing. I tried hooking up an autometer tach and it would work under 4000rpm, but when the HEI module got warm, the tach would go crazy bouncing all over no matter what rpm. I should note, I have the HEI module bolted to a gigantic aluminum heat sink that was used for a voltage regulator so it doesn't get that hot. Am I missing something? I really would like to get my tach working before the drag strip opens this spring. Sigh.. Quote Link to comment Share on other sites More sharing options...
vashonz Posted March 4, 2007 Share Posted March 4, 2007 I would check the plug wires. I had a problem where my RPMs were jumping all over the place, and it was due to cracked ignition cable insulation. This caused interference with the tach signal. When I replaced the cables, the problem was solved. This was with SDS, but I imagine the megasquirt may be similar. Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 4, 2007 Share Posted March 4, 2007 If you have some unused spare pins in the 37 pin connector, you can drive the tach with the MS tacho output. http://www.msextra.com/manuals/MS_Extra_Hardware_Manual.htm#tachoout I've run th stock 280Z tach off the coil - terminal. I used a 470 Ohm resistor in series with wire going from the coil to the tach. I switched to EDIS, so no I use the tacho output pin on the MS. You need to add a little circuit to the MS to do it (see link above). Quote Link to comment Share on other sites More sharing options...
Metro Posted March 4, 2007 Author Share Posted March 4, 2007 Forgot to mention, I've tried setting up the tach out, but it usually ends with me breaking megasquirt and having to replace a bunch of diodes. Quote Link to comment Share on other sites More sharing options...
Metro Posted March 13, 2007 Author Share Posted March 13, 2007 Well, it looks like my best option at this point is to try the tach output again. I think where I went wrong was confusing s12c and s12 for the 12volt source. I'm not sure what's the difference between those two but obviously it wasn't right. That being said, do you know if there's a connect x to y, guide for doing this? I'm not all that great about reading diagrams. Quote Link to comment Share on other sites More sharing options...
Metro Posted March 19, 2007 Author Share Posted March 19, 2007 Ok well, I redid the tach output connecting to a proper 12 volt source (used the outside pin on the voltage regulator). The tach needle actually moves again, so there's some progress. The bad news is, it looks like there's some sort of interference because the tach will jump around randomly and then go nuts over 3 or 4,000 rpm. I'm not really sure where to begin troubleshooting this, so does anyone have any ideas? Another thing I noticed, the car misses when the tach jumps around so it's definitely affecting performance as well. The rpm readout in MS is perfect tho, only fluctuates because of the slight miss. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted March 19, 2007 Share Posted March 19, 2007 The MS'd ZXT was doing this a while back, and it was due to a dead (dying) HEI module. If the HEI module is NOT properly grounded or cooled it will give erratic outputs and eventually quit working. You can take the module to NAPA or probably other stores and they can plug it in and test it. Improper ground and cooling kills these things like none other... Mario Quote Link to comment Share on other sites More sharing options...
Metro Posted March 19, 2007 Author Share Posted March 19, 2007 Well it definitely has good cooling now, but before I bolted it to a massive heatsink it definitely got hot enough to burn flesh if you touched it. Fortunately, I have a spare module I can try. Thanks Quote Link to comment Share on other sites More sharing options...
Metro Posted March 22, 2007 Author Share Posted March 22, 2007 Well with the other HEI module, it does work considerably better. It still will "tick" ocasionally and after reving it up and letting off the gas it goes bonkers as the motor slows down. So it's usable, but it's not where I'd be happy with it. I think I might try using the VB921 for spark again. The first time I attempted to hook it up, I was horrible at reading wiring diagrams, now I should do ok. So we'll see.. Quote Link to comment Share on other sites More sharing options...
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