So after a bad case of strep throat (group C streptococcus, cultured and immunotyped it myself), I finally have a chance to get back to work on my brother's Toyota ('91 pickup, 22R-E, manual trans, MS-II v3.0 board, relay board). I'm using a 8 pin GM HEI module from a ~89 TPI Camaro (the Toyota's factory VAST module was bad) getting its signal from the 4 vane VR sensor in the Toy's distributor. The truck fires up ok, even at ~15 degrees F (gotta love Michigan winters), although it does run rich; the tach signal is rock-solid, although the IAC valve is stuck open causing a high idle from ~1800-2200 rpm (depending on position of idle fine-tune set screw); this probably isn't relevant to the observed problems.
The problem comes when the MS should be taking over timing control; it never happens. I set up the relay using a 12V switch that my brother had for some off-road lights; at the terminal that goes to the module (pin B) I consistently get ~4.9 volts, which should be enough to trigger the transition to MS-regulated advance, right? I checked continuity of the wire from MS pin #36 (through S5 on the relay board) to pin E, which was fine, so the timing control signal should be received by the module from MS. But when I flip the switch, no change in timing occurs; the only difference is that timing becomes somewhat erratic. It also seems that the engine occasionally misses an ignition event, but that may be due to a cheap timing light, not a legitimate problem.
So, does this sound like a faulty HEI module, or a problem with the MS? My interpretation of the HEI blurb on the MS webpage is that once the transition to MS-controlled timing occurs, the MS is entirely responsible for coil control; if this is the case, then it seems the problem almost has to be the module, that it is not getting the signal to switch out of limp-home / start mode. Since it is getting the 5 V signal, this seems to imply that the problem is internal to the module. If the transition did occur, and the MS was solely responsible for coil charging, if there were a problem with the MS where a signal was not being generated, the vehicle should die. Alternatively, if the module is more intelligent that I think, and takes the signal from MS, using this to modify the default settings, then the problem could be the MS. Regardless, I think the first step is replacing the module; shouldn't be too expensive in the junkyard. Any input?
MS-II not taking over from 8-pin HEI
Moderators: jsmcortina, muythaibxr
I do have a timing map loaded- but what do you mean by "fixed angle"? I'm using MS-II and a v3 board with MegaTune 2.26; by my recollection there is no setting for "fixed angle", the closest thing is "trigger offset". Isn't the -10 setting used by MSnS-E to tell it to use next cylinder mode? Also, when I attempt to change trigger offset by using the wizard, nothing appears to happen- no change in timing, so the lack of a map- even if for some reason it was not loading, which I think it should be- would not matter. I think...
I should have clarified that. My brother was checking the timing with the timing light while I was changing the timing using the trigger wizard, there was no observed change in "real" timing as determined by the timing light. Since I'm fairly confident that the bypass wiring is working correctly- that ~4.9 volts on the correct terminal of the relay should be all it needs- I think it probably is the module. Or, perhaps, I managed to damage the MS ignition output circuit during one of my other tuning disasters. Either way, I guess I'll start with the module, and go from there; am I right in thinking that the MS totally handles coil control once the transition to computer control occurs? Or does the module just use computer input as an additional variable to modify its control of the coil?
Is there an advantage to using the VB921 to drive the ignition module as detailed in step #65 of the V3 assembly guide? As opposed to driving the module directly from the processor port? It seems to me it would shield the daughterboard that much better from ignition feedback- not that this should ever occur, but the unlikely seems to happen with uncomfortable frequency when I'm playing with electrons... It looks like a 5V pull-up would be appropriate for the HEI module, and the spark output has to be inverted, but other than that the software settings are unchanged.