Cannot start
 

I tried to crank my rx8, it can crank but no sound at all. Battery is at 11.6V. Just change the starter. Still cannot start and security indicator light keep blinking. Anyone can help?

11.6 is a drained battery. If it is turning the starter at all, its not turning it fast enough.
Charge and try again.

If that doesnt work, please clarify what you mean by cranking. Is the starter spinning? Is the engine spinning?

It is a 12V battery, is 11.6 is considered drained? Usually in idle, the battery sold here is at around that level. When the engine start the battery meter will usually boost up to 13.8.

When the car is off, it should read around 12.3V~12.6V. When idling, it should ideally be around 14.1V.

Battery voltage isn't linear BTW. A small decrease in voltage can mean quite a large change in the amount of charge you have left.

Yes. If it ever drops below 10.5V you're in permanent damage territory.

Thank you all for info. Will send the battery back to shop to get explanation as it is a new battery

Sometimes that happens. These things sometimes can get stored for a while and when you get it, it's DOA.

And blinking security indicator, you said? Do you have the normal Keyless Entry or the Advanced Key(card key)?

Yup. Security indicator blinking. The engine was upgraded from 4 speed auto to a manual 6 speed 13B-MSP Renesis. Still using key. Just a different one. Now the engine can already be started. I ve change the starter. Got it from a half cut shop. The starter was from a 5 speed. When i had just completed changing the starter, i tried to crank but still nothing. I was just then switch it on and off a few times and suddenly my rx8 is alive back. Still it is like a slow start up. I dont think that it was due to compression. But still, i dont know the exact problem.

Did you also change the ECU to one from a 6 speed?

Yupz ECU was changed.

What year is the new ECU out of? What year is the car?
The immobilizer sysyem is built into the ECU and requires that the ignition key cylinder is paired to it. In the later models with credit card key, things might be a bit different. Long story short, fon't expect your original key to start the car. You need the key and ignition cylinder from the car from which the ECU came, or bring it to Mazda to have your selection of keys and computers paired.

The ECU came from the same engine. Have been using it for years. It was fine through out the years.

Check to see if your terminals are clean and tight.
They can stretch over time and even though the bolts are bottomed out, they could still be loose.
Also check your ground wires, they can get corroded and lose contact.