Depends on the year: 02-05 4tec are stored only in the ECU, gauge has no memory and only reads the ECU for hours. 06 and newer are stored in both the ECU and the LCD gauge, whatever hours the gauge has on it is what it will show on the gauge even after married to a new ECU but if you connect BUDS you'll be reading the ECU hours. The old 2 strokes also stored hours in both the MPEM and the gauge.