MS2 upgrade, Key-on pop returns...?
 

I didn't change my spark output circuits, they are just like they have always been since I changed them to Joe's improved circuits. What is different about the MS2 that causes this? It happens just about every time and sometimes fouls a plug and runs on 3 for several seconds after startup.

Did anyone ever swap out fuel injectors and get this issue to stop?

theres no reason being on ms2 should do it.

What injectors are you using when it does the pop?

RX7 550s.

It pops as soon as I turn the key to ON. Just like before doing Joe's spark mod. WTF?

This may or may not be helpful, but,

I had a no-start issue due to a crank sensor that had gone bad. While the car refused to start, I would get a definite pop when I turned the key on.
Once I replaced the sensor the "key on pop" thing went away.

I can't tell if it could have been line resistance, etc playing a role in the absence of a proper crank sensor, fooling the corresponding ignition circuitry in the ecu. Never bother to test and diagnose as I had more pressing no start problems.

I had stock ECU and stock injectors, btw.

Well ya that makes sense if you're cranking a bunch of fuel into the combustion chambers but not getting spark. Then when you do get a spark its going to ignite.

My question is that with my inverted spark outputs, how the hell is this popping now when I turn the key on? I'm thinking I just finally need to ditch these RX7 injectors and get something better.

I had the same issue with rx7 460's. They are pintle type and my stock injectors (which I don't get the pop with) are Bosch type. Rx8 425's are also Bosch type, I have a set, but never tried them yet.

I have the same issue and created a thread like this, someone replied and said it was his injectors. Mentioned after swapping to newer ones he didn't have anymore popping. He had old rx7 460cc same as I run. I also have the joe spark mod done.

Now the 3 cylinder thing maybe a seprate deal. I would wake and go to my car in the morning, start it up and notice it running on 3 cylinders and finally it would go back normal. Well finally one night it went below freezing. So I go to my car next morning and find it won't fire up and start. Turns out my coil packs were going bad. Swapped in my spare coil pack and it started right up. Swap your current coil packs with a spare if you have some and see if that changes whats going on.