13bt S4 stock

Sometimes, both cold and hot, when starting the engine one of the rotors does not burn.

If I crank it up for a while or drop it in hold I usually recover that rotor that doesn't work and it starts up.
Other times I have to leave the car stopped for a while, also random, and when I start it again everything goes well. It tends to do it more when hot, either by use or weather temperature.

Any ideas? The injectors work because when this happens it smells like unburned gasoline, plus I had backfire today because of this. (Yes, I will never try to run it again by cranking it up). What's left is the ignition system. New spark plugs and wires.

Is there any way to test the coils? Other than see if the spark works.
​​​​​​Any way to put new non-original coils without the need for a new management system?

 

by the random and intermittent nature of what you describe, i would suspect one of the ignitors as opposed to the coil itself failing. you have identified heat being a factor, and i think that points more to the ignitor.

i've pulled a few Gen 2 coils apart and have noted that sometimes wires inside can be in rough shape. maybe you can start there. you might get lucky and find something that you can fix. beyond that, i don't know if there is a test procedure, but if there is, you can start by looking in the FSM.

some links
Foxed.ca (get a copy of your FSM)

these links are Gen 1, but maybe they can help.
https://www.rx7club.com/1st-gen-arch...nitors-742083/
https://www.rx7club.com/1st-generati...works-1070706/

 

If there is smoke you could have a coolant seal leaking into the combustion chamber. If the car is stock it's probably just an old injector bleeding off the fuel injection line pressure because it's leaking and flooding the chamber/spark plug until you have enough rotations to clear it up.