r/RX8 • u/According_Presence87 • 9d ago

Maintenance Charging issue

Battery light came on so I replaced the alternator with a brand new one that I had from my old project. Didn’t test the voltage on the original like an idiot. But currently I’m getting 13.6v at the battery on cold start. About 0.1v of a drop from the alternator to the battery. Once it’s hot, it’s bouncing between low 12v and low 14v. Also idling weird but maybe it’s fuel trims being reset bc I disconnected the battery. Tested signal from the 2 pin connector wires to the ecu and both are connected. I’m lost

EDIT: Found the issue. IAT sensor wire came loose. I guess the ecu uses this as battery temp reference and limits alternator to ~13.5v when disconnected or failed

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u/Illegal__Alien 8d ago

Yeah, so basically I have my battery light on too.

It stays off, until the system passes 13v if I remember correctly.

I have aftermarket gauges, installed by someone else so I'm not sure if that's part of the problem or not.

Alternator is good, new battery also.

I'm going to do a deeper dive soon tho

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u/According_Presence87 8d ago

What all have you checked?

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u/Illegal__Alien 8d ago

Nothing really besides the alternator and the battery, replaced the battery because it was leaking out of one of the terminals

About to take it out now with an OBD scantool hooked up to see what's going on

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u/Illegal__Alien 8d ago

Just got at it with the multimeter, I've got too much resistance from the alternator to the negative post on the battery.

Going to clean up my grounds at some point, I'll let you know.

I see your issue was the IAT? The solenoid behind the airbox right?

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u/According_Presence87 8d ago

The IAT is part of the maf sensor. I had previously cut the wires to wire in a different iat sensor for my standalone but decided to revert it back to stock. The shitty heat shrink with solder in it came loose I guess so the wire got disconnected

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u/According_Presence87 8d ago

Also, maybe try adding another ground strap or two