Selecting correct replacement ECM for my rx8
 

The rx8 (2004 6spd sport from CA) I have has a damaged engine computer because a previous owner of the car hacked into it a bit. I need to buy a used replacement computer. How do I make sure I'm getting one that is the correct match for the car? If I get the right computer, I should be able to plug it in and drive without any setup, correct?

So... not possible?

not exactly...you have to either have it programmed by mazda to suit your particular car....or have the immobilizer bit turned off, so your car will start. I think there were also some changes thru the years, so the codes on the ecu should match as close as possible - they reflect model yrs or manufacturing changes I believe, as well as auto/manual models.

You need to have the ECU rebuilt with "as built" data from Mazda....so the different CAN Bus units can talk to each other :)

Hmm ok looks like i'll have to stick with the one I have.

whats wrong with your current one? what do you mean by hacked in?

Kind of a long story but...

One of the previous owners of the car had been running a turbo rx7 engine in the car to get more power but he still wanted to use the stock dash so he soldered the crank angle sensor pickup directly onto the ECU pins. Stupid plan to begin with but whoever did it was a bumbling fool and melted the plastic connectors around the pins badly and broke one of the pins off and somehow damaged the unit internally. I put a 2006 engine back into the car and cleaned up the ECU pins as well as I could and replaced the broken pin. The engine runs fine but I got a CEL for a problem with the O2 sensor. I had just put in a new O2 sensor and couldn't figure out what the problem was so I took the car to the dealership to get them to diagnose it and apply MSP16. They found that the O2 sensor and wiring were fine but the CEL was caused by the internal damage in the ECU and they were not able to reflash the ECU because of the damage. They were going to replace the unit under warranty but because of the plastic damage they had to reject it. So now I'm stuck with an ECU that runs the engine but will never allow it to pass emissions or have MSP16 installed, which kind of sucks.

So get another PCM and take it back, and have them reprogram your existing ignition keys and as built data (for the power steering, abs, flash, etc.) into the new PCM.

I'm told that most any MT pcm for s1 rx8 should be able to accept the above mentioned data for any s1 MT rx8. I had several discussions about this when I was doing research for my AT to MT swap on my 04. I used an 05 MT PCM (along with engine etc.) in my 04 AT, and about 45 minutes of programming at the dealer took care of it.

I had assumed that was possible but they insist it is not. What a pain. I'll press them further on it.

I guess you didn't understand the 1st time I mentioned it. Perhaps the dealer can't or won't do it. Doesn't mean it doesn't work however. Just get a similar ECU, get the immobilizer bit turned off (Racing Beat for example) so your original key will work, and you're good to go. It's the immobilizer that's the problem. How do I know? I bought a random ECU (similar markings) off ebay for my '04 MT, had the bit fixed, installed and it works great. I have it sitting in my shop and I can swap with my original and off I go.

New ECU
 

I'd like to do something similar with 2 ECUs ... How did you go about setting the "immobilizer bit" on the second ECU? Do I need to get somebody to do this for me?

I think Renesas fixed the 'immobilizer bit' access in 2005, so only a 2004 ECU can be bypassed.

Both ECUs I have are from 2004 AT RX-8s. What do I need or need to do to set the bit in these ECUs?

Racing Beat can fix it for you, and/or also install a stock tune... I'm not sure if a Cobb unit can do it, but someone must know, perhaps MazdaManiac.