Second HEI8 Pin Module Failed

[mmorters]

Hello, first post for MSII 2.2 rev 2.92. Using GM 8 pin on 406SBC with small cap HEI external coil. Just got to the point of first starts and had it running a few times in the last couple of days. On the last run a few days ago I noticed that the coil was getting hot and also the bottom of the dist at the module. I saw a little smoke at the coil and it had melted before I could unplug it. After reading and checking the basic set up I noticed that I had the dwell set at 3.1 ms and not the 2.5 recommended for external coils so I changed that setting and bought another coil. Also reviewed my dwell/battery voltage compensation chart and it seems to still be set at default settings. After installing the new coil there was still no spark and the spark plugs were found wet again. Dried everything out and double checked wires to dist and coil. I am using the FIdle relay and the spare port settings to apply 5vdc after start. Came to the conclusion that I might have burnt out the module after checking wires and after installing a new module it fired back up and idled AND the coil/module remained cool, but it soon died and further attempts to start showed the same wet plugs with no starting. So I think I have burnt up another module and wanted to check here to see if anyone has had similar issues ( I searched and read almost fifteen pages in this section). I am unsure how the modules can be checked (except buy another one and install). Any ideas what might be going on here?

[mmorters]

While waiting for a reply here, I went over my basic ignition set up again and noticed that I had "spark output" set to "going low" (default setting) but when I read the manual it states to set this to "going high" for GM 7 & 8 pin modules. Does anyone have any experience with having this setting opposite and ruining a module ( or two)?

[Bernard Fife]

mmorters,

I have no experience of setting this the wrong way and ruining modules, but I do have lots of experience with the correct settings and no failures (on my 406 sbc). I imagine setting it the wrong way would be bad for both the module and the coil.

Lance.

[DonTZ125]

I believe it. With dwell duration getting into double-digits (quite possibly into triple-digits while idling), you fried one or more of the internal coil driver transistor(s). Getting your tach-in signal polarity wrong means your car doesn't work properly, if at all. Getting the ignition-out polarity wrong breaks hard parts, whether drivers, coils, or - if you're lucky - just a fuse.

[mmorters]

I appreciate the input. Now I can move on effectively with that knowledge.

[mmorters]

I can confirm that the module was ruined by not having the correct setting for spark output and that the coil was fried by having the dwell set too high. The default setting for spark output is going low and the GM 7/8 pin needs to be going high. I installed a new module and it fired right up (after confirming the new settings change). This project has taken me 10 years to put together and it is really something to finally see and hear it fire up and sit there at a nice idle. Ok, so on to tuning now. I haven't installed an EGO yet but it is next. I've been looking at the available wide band DIY.

[Bernard Fife]

mmorters,

That's great! I know how exciting it is to see the light at the end of a long project!

While you are waiting for an EGO senor, you can certainly tune the idle, warmup, and the accel enrichments as well.

For example, for the idle, you want to tune to get the minimum MAP kPa value at your chosen idle speed (likely the speed where it is smoothest, but other factors often come into play). You do this by adjusting the VE table at the cell where the engine is currently idling. MAP will likely go up or down as you change the VE table cell. If MAP kPa goes up when you decrease the VE table value, then you need to increase the table value (and vice-versa). You will probably have to adjust the throttle stop several times to keep the idle speed where you want it. (This gives you the most efficient idle AFR. Note that many emissions controlled vehicles operate at a stoichiometric ratio at idle rather than the most efficient AFR in order to provide the best mixture for the catalytic converter - but MegaSquirt isn't for emissions controlled vehicles, of course.)

You can also work on you cold start/warm-up and accel tuning without an EGO sensor. For example, accel tuning is best done in nuetral when not moving, as the the rate of change of rpm is highest (and thus the need for accel enrichment is greatest). See:

http://www.useasydocs.com/details/us3tune.htm#accel

http://www.megamanual.com/v22manual/mtune.htm#csenrich

Because these values all interact, you likely won't have the ideal values until you finalize your VE table (with your EGO sensor) but it will give you a huge head start while waiting for the sensor.

Lance.