1986 Mazda RX-7 FC s4

13B NA

Stock ignition and ECU



My car is a crank but won’t start

The tachometer bounces

There is good fuel



Here’s what I’ve already tested. I’ve done a bunch of troubleshooting that I’m starting to second guess myself but I think this is everything



Battery is brand new.

Spark plug wires ~1 year old

Spark plugs brand new

Checked CAS resistance = good.

Checked coil pack resistance = good.

Harness side Black/Yellow wire has steady 12V with key ON.

Coil pack itself still reads 0V when plugged in.

Tried a second coil pack/igniter — same result.

Cleaned coil/igniter ground.

Still no spark output.



Does this sound more like an igniter failure or ECU failure on an FC? Anything else I should test before swapping parts?

thank you for looking!

 

Time to do a compression test. You'll save yourself some headaches if you know the health of your engine.

 

it's been a while, but as i recall only the leading fires on cranking, so if you're basing this off your trailing ignition then you will keep going in circles when the problem is somewhere else. IF the tachometer is bouncing, it should be sending a signal to fire your coils, it basically means your ECU is processing the cranking and sending out the appropriate outputs unless your computer, harness or coils are burned up.

a timing light can be inaccurate way of determining spark, so can old worn out plugs.