Initially battery died. Had it recharged as it is still good. Car wont start so i tried the 7 second hold down the accelerator method as per Mazda. Still no start.

Researched where the ecu reset helped in this situation which i am going to try.

My question......i was planning on disconnecting the negative battery terminal when not in use as sometimes it sits for weeks. (a battery tender is less practical for me). Will i have to reset the ecu everytime i disconnect the battery?

 

It already resets when you disconnect the battery for a little while. Just 10 minutes and your car will forget all the fuel trims, emission status, etc.

If you are talking about the 20 brake stomps, that's just for the ESS profile, which is usually not needed, but since it costs nothing to try, it's usually recommended as a part of troubleshooting.

 

I spoke to someone who could not get it started like myself. He did the 20 stomp and his started.

Do you see an issue if i disconnect the battery every time i think the car may sit for weeks?

 

Disconnect away. Just make sure you let it idle and warm up fully before driving after reconnecting. It needs to relearn to idle. A healthy car should behave fine. If you continue to have issues, there's an underlying problem.

 

I'm going to disagree with part of what Loki said.

Agree:
Disconnecting the battery is fine. Do it as often and for as long as you like. The car will lose it's memory of fuel trims but it will figure them out again on its own.

Disagree:
You don't need to let the car fully warm up at idle before setting off after disconnecting the battery. In fact, this won't work the way you think. The RX-8 ECU (and maybe others) has 3 separate fuel trims for different amount of air entering the engine (as measured by the MAF). The trims for for < 8 g/s, 8-20 g/s and > 20 g/s. The computer constantly watches the O2 sensor and adjust fuel to match the desired AFR. It averages these short term changes over time into a long term trim. However, it only does this once the engine is warmed up. So, letting sit and idle will make it take longer to start the re-learning process because it takes longer to warm up by idling than it does by driving.

Additionally, at idle, you should only be pulling in 4.5 - 5.5 g/s so even if the car were fully warmed up for a while, the car would only learn the lower trim. It won't do anything for learning the other two.

While the engine is relearning fuel trims, idle may be rough and it may stall while it's cold (because the ECU is mostly guessing at what it thinks is needed). This may require several drive cycles to clear up.

 

^^ that's a good point, I agree. That last paragraph is the part you need to remember most.

 

If it does idle rough and stall, wont this cause it to flood? Should i rev it a bit to keep it from stalling?

 

If your engine, starter, battery, and ignition components are healthy, it won't flood.

 

 

You gotta turn the steering wheel from lock to lock after reconnecting the battery.

 

Yah, that's the steering angle sensor profile. Start the car and turn the wheel lock to lock like Jin said.

 

 

Tried on both my RX8's after turning steering wheel lock to lock DSC light goes out but not traction light. This will only go out if i shut off and turn back on

 

That is correct.

 

Same thing happened to my rx8 it used to start but now it’s completely dead and before it would turn on and heat up right away. The overheating would be caused by a bad thermostat correct?

 

Dead as in, nothing comes on? Is the battery drained?
Overheating can have many causes, not just the thermostat (usually not the thermostat)

 

I might have to check it, why would the car be heating up now? After someone placed the battery wrong