Voltage spiking

Year/Make/Model: 2007 Mazdaspeed 3
Mileage: 186000
Location/Alitutude: Houston, TX
Concern: Voltage spiking to 18v intermittently
DTC's: P2503, P2504, U140
Modifications: CS cold intake, CS downpipe, accessport, HPFP
ECU/Tuning Software: Cobb Accessport stage 1+
Tuner:
Is the concern intermittent? Yes
Can you duplicate the concern? Yes
Recent Repairs: Just changed out the alternator

Really not exactly sure as to why this is still an issue even after changing out the alternator. Is it possible I need an ecu reset? Not super familiar with the car yet, helpis much appreciated!

 

Is the voltage regulator integrated into the alternator on these cars

 

I'm not terribly sure, my searches has been quite obscure when it comes to this car. Not a lot of sources covering MS3's electrical problems

 

3 wire I think; I run a 1 wire so I get the occasional battery light when the ECU expects the alt to push 14v but only ever runs 13.8.

Ecu has to hit the coils with a starter voltage...Maybe check all the connections, major grounds, hit the contacts with a wire brush?

Also post what the codes mean, don't make every individual person coming to this thread google them.

 

Wouldn't bad connections result in lower voltage than expected rather than spiking? Genuinely sorry if I sound stupid I am not at all familiar with this field.
P2504 is for system over charging, P2503 is for system undercharging but that code has since then went away, U0140 is a communication error to BCM.

 

They are called electrical gremlins for a reason. High enough voltage could cause an insulation breakdown and make the voltage spike...I've heard of weirder shit happening.

 

How peculiar, do you suggest any major points I should go after first? Other than the ones you've already mentioned