Voltage dropping while driving

[Bsalinaz]

So I have an s13 with a 1jzgte I’m having an issue with my voltage reading 12.5-13v at idle at the ecu but as soon as I drive the higher my rpm the more my voltage drops about down to 11.5v. I checked at my battery and I’m reading about 14v at idle. Also noticed when it’s cooler outside my voltage doesn’t drop as much? I have grounds from the harness to the block and from the block to the chassis also the battery is in the trunk and ground is to the chassis I’m confused on what’s drawing power while driving could this be due to a bigger fuel pump? 

[jigga009]

I'd probably get the alternator bench tested to rule any issues out with a blown diode or similar, and then start voltage drop testing your power wires between the battery, alternator, starter motor and main fuse box in your engine bay during a cranking event. You may find a high resistance connection in there causing your issues. 

Also be sure to check alternator belt tension also to ensure the alternator belt is not slipping when you load the car.

[Bsalinaz]

Not the alternator I’ve checked the alternator and wiring from starter to the fuse box and I’m not dropping voltage on any of these including the battery, it only happens to the ecu under load so I’ve contacted wiring specialties to see where the ecu is getting power cause I’m getting a voltage drop on that wire which I just found today but none of my connectors are labeled power. I did run a separate wire to double check and sure enough I was stable at about 13.5v even under load