Hello, I just picked up a 2005 manual Grand Touring. I have been going over the car inspecting everything thoroughly and I am having an issue where the alternator seems to be overcharging the battery.

So far I have put a multimeter on the battery and it reads around 14 volts not running, when I start the engine and put the meter on the battery it'll Spike to almost 18 volts and will begin to leak acid out the top. I have a light on the dash for the battery and the power steering.

So far I have cleaned all the grounds in the engine bay following instructions from the DIY forum. I'm at a loss as to what it could be now. Research says it could be a faulty PCM but I want to ensure I have checked everything else before going that route.

Any help would be greatly appreciated!
Cheers!

 

The voltage regulator is part of the alternator assembly, sounds like it has failed.

 

hi, do you have the issue resolved,
i got the same issue if i go high in rpm

 

A new alternator solved the issue for me.

 

First a battery wont hold 14V on it with the engine off, for a long time. Voltage will drop to 13V quickly(minutes), then remain at that level or slowly drop down to 12V if the battery is old.
Now the target voltage for an RX8 ECU when charging the battery is 13.5V in the summer and 14.4V in the winter. If it gets too high then, 99% probabilty, the alternator needs inspection and/or replacement.

 

Im running into the same issue with a P2504 code, loss of eps, dash lights etc. Brand new battery and a reman alternator form the mazda dealer. I'm suspecting a pcm failure so im gonna diag it tmr.