seth1001 Posted September 25, 2011 Share Posted September 25, 2011 I've spent the last 7 or 8 months working on my 1980 280zx NA...so far I've got MS3 v3.0 in there and it's working for the most part. Anyway, I could never get the stock distributor to get a tach signal to the MS3...it just wouldn't work. So I ended up getting an MSD 6al box to generate the tach signal and hopefully improve performance albeit slightly. For the most part it's been promising, but I'm having a huge problem with RPM spikes going to the MS3. I've driven the car a lot and come to the conclusion that the problem lies outside of the MS3 settings. I've tweaked the RPM lagging but the spikes are too intense to get around it that way. I also disabled the fuel cut to see if that helped...not so much. Basically it happens whenever I up the load, or up the RPM, or both. I can't drive the car above 2500 without getting spikes up to 30,000 rpms showing up in tunerstudio. It also happens a lot when I up the load, even if the RPM's are below 2000 or so. The rpms spike and the engine bogs down. So...that's the situation. The forum wouldn't let me upload so here's a link to the log file. Any suggestions for me? Thanks. http://www.mediafire.com/?ylma6va2rlrh48s Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted September 26, 2011 Share Posted September 26, 2011 Did you build the box? You're basically running of the coil "-" (negative). There's some things you can change to make it more resistant to noise. Check the build instructions at megamanual.com Quote Link to comment Share on other sites More sharing options...
seth1001 Posted October 5, 2011 Author Share Posted October 5, 2011 Did you build the box? You're basically running of the coil "-" (negative). There's some things you can change to make it more resistant to noise. Check the build instructions at megamanual.com It's not running off the coil negative with my setup. The MSD box is being triggered off the VR and the Megasquirt is being triggered off of the MSD box. Quote Link to comment Share on other sites More sharing options...
NewZed Posted October 5, 2011 Share Posted October 5, 2011 Have you tried a different alternator? And do you have the capacitor on it? There's more to "noise" than radio interference. The alternator can generate a lot of "noise" that can affect electronics when it goes bad. Just a possibility, I'm no electronics expert. But I have seen a couple of solid-state devices destroyed or damaged, specifically a radio and an ignition module, as a result of slowly dying alternators. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted October 6, 2011 Share Posted October 6, 2011 It's not running off the coil negative with my setup. The MSD box is being triggered off the VR and the Megasquirt is being triggered off of the MSD box. True, but I think the concept might be similar. Take a look at the assembly instructions at megamanual.com, I think the MSD box's output might be too noisy for the way your box is built. Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted October 6, 2011 Share Posted October 6, 2011 Hi Seth, Could you be a little more specfic about how you are triggering the ignition. Normally, the MSD box fires the coil and Megasquirt is triggered off of coil negative as Mario assumed above. Are you connecting the MSD coil + and coil - wires to Megasquirt or using the tach out? Or something different? I looked at your Log and you certainly do have some serious rmp spikes going on. Quote Link to comment Share on other sites More sharing options...
seth1001 Posted October 28, 2011 Author Share Posted October 28, 2011 Hi Seth, Could you be a little more specfic about how you are triggering the ignition. Normally, the MSD box fires the coil and Megasquirt is triggered off of coil negative as Mario assumed above. Are you connecting the MSD coil + and coil - wires to Megasquirt or using the tach out? Or something different? I looked at your Log and you certainly do have some serious rmp spikes going on. That wiring scheme is actually not possible with an MSD box. The multiple spark discharge fires the coil multiple times for every spark discharge. If you wired the Megasquirt box to the coil negative with that setup, the megasquirt would think your engine rpms were about 4 times higher than they really were, which is why every MSD box has it's own RPM output which is what I'm using. It puts out the exact same square wave 12v signal that the megasquirt is looking for. I actually HAD to use the MSD because my megasquirt refused to fire off of the coil negative pre-msd box...presumably because there was too much noise in the electrical system. I don't have the money or justification to buy an oscilliscope at this point so...that's where we are. In response to the comment about the alternator, actually I just installed a brand new alternator about 2 months ago. I'm planning on getting some magnecor wires and a new coil to reduce noise but I can't imagine that alone would solve such extreme RPM spikes. Would a battery negative grounding kit increase noise?...I've got one of those on there. I don't have any idea what else could be causing so much noise in the system. Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted October 28, 2011 Share Posted October 28, 2011 That wiring scheme is actually not possible with an MSD box. My car would be inclined to disagree with you. As you know, the MSD6 box tach out is a 12V square wave. According to the Megasquirt diagrams I've looked at, you would run the MSD tach out to Pin 24. I recall trying this without sucess. Megamanual diagrams show Pin 24 accepting VR, coil negative and hall sensor. Hall Sensors are a square wave output so it should work. Perhaps you can slay this little gremlin and teach us all something. Or another member who runs this set up sucessfully could chime in. Good luck. Quote Link to comment Share on other sites More sharing options...
seth1001 Posted October 29, 2011 Author Share Posted October 29, 2011 My car would be inclined to disagree with you. As you know, the MSD6 box tach out is a 12V square wave. According to the Megasquirt diagrams I've looked at, you would run the MSD tach out to Pin 24. I recall trying this without sucess. Megamanual diagrams show Pin 24 accepting VR, coil negative and hall sensor. Hall Sensors are a square wave output so it should work. Perhaps you can slay this little gremlin and teach us all something. Or another member who runs this set up sucessfully could chime in. Good luck. I'm not sure exactly what you're getting at. You seem to be implying that you can run a megasquirt box triggering off the coil negative with an MSD ignition system, which as I explained is not possible...for the reason I explained. I think you may have misread what I was saying. It's true the megasquirt can trigger off of a coil negative, VR, or hall sensor; though the board would have to be reconfigured for each one. The issue is simply that it wasn't working that way on my car. The coil negative wouldn't trigger the computer at all and the VR put out a very unreliable signal. And I don't have a hall sensor in my ignition system. Now I've got the MSD box, which WAS able to trigger off the VR, and the megasquirt receiving the tach signal from the MSD box's tach output. My problem now is that there's some kind of interference in the system, and I can't figure out if it's starting at the VR or coming from the MSD box or both. And because of that fact, I don't really have any idea how to go about fixing it. Quote Link to comment Share on other sites More sharing options...
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