I managed to narrow my turn on problem to the fact that te M4 does not pulse the motherboard when in the HARDOFF state. Details in here
I also purchased an M4-ATX in the hopes I could escape the dreaded "Turn on" issue that I had with the M2-ATX.
HOWEVER, I STILL have the "Turn on" issue! If I go to start the car, I see the case fan spin up, CPU fan spin up, and it appears the PC is cranking up. But, after about three seconds, it all goes black. It looks like power is just simply removed (exactly like the issue with the M2). Since I have a rocker switch on the 12v "Ignition" line going to the power supply, I can cycle the ignition pulse going to the power supply. After the car has started, I go from on-off-on from the rocker switch and my system comes alive.
I just spent $130 to escape this very issue with my M2. I'd like to determine if it's my system or the power supplies. I've checked voltage (~12v on power wire, 12v on Ignition line, Ground is good). I've tried different "Ignition" sources (mirrors, ignition, fuel pump, etc) to trigger the power supply on. No change. I'm open for suggestions or the answer to this problem.