you may have read that wrong. obd codes are 4 characters. p027b is a code for fuel pump command issues.
Do that with car running. Battery voltage static won't tell the story. Also check for AC voltage; aka AC ripple. High presence of AC is indication that alternator voltage rectifier is faulty. Flaky voltage can cause problems. In fact there is a voltage table in the tune that corrects for pulse duration of he fuel injectors as voltage fluctuates. 13.8 -14.0 is considered operating voltage on most. As voltage drops below that the injector pulse duration becomes longer slightly or shorter slightly as voltage may creep above 14.0vdc to assure the most accurate fuel flow is provided as the voltage system regulates. get below a certain voltage which often indicates a presence of AC voltage and things can start going haywire. Crank triggers, cam sensors, fuel injectors, MAF sensors etc all start providing incorrect data which leads to odd issues if the alternator goes whacky. More commonly seen in the older 05-09 S197's due primarily to their age but also happens on newer models as well. AC is not a good thing on a DC bus. Sagging voltage is also not a good thing.
I'll watch the battery voltage with the car running. I guess I underestimated how sensitive these cars can be. I've had my Mustang for about a year now and this is the first real issue I've encountered. Realistically, I'm sure it's related to not leaving it stock.
