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Which ECU are you using? Manual or auto? The states of these two lines vary depending upon ECU.

Does low-voltage when cranking cause you problems with going over 4000-rpms later? Where are you getting this info? Connect external diagnostic tach to verify dash tach is reading accurately.

Due to voltage-drop during cranking, you're not gonna get above that 10.46v you've measured. Way around that is to store up higher-voltage BEFORE cranking. Then feed it back to that line while it's cranking. Can be done with capacitor, diode and current-limiting resistor.

STA connects to starter circuit, so should only have +12v when cranking, otherwise it's grounded.
NSW should have +12v only when cranking. Then grounded after ignition released from START position.
STA & NSW should NOT be attached to power OR ground. They should be connected to relay that feeds it +12v when cranking, and grounds it all other times.

BTW, how is any voltage even possible on that STA-NSW connection if you've got it grounded? Would be blowing fuses or frying ECU.
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