i have a 1997 ford expedition running rough, like bad timming. replaced ecm still rough. i hooked up a code readed, indicates nothing. hooked it up to my 2001 f-250 and showed air ratio and fuel ratio. checked all fuses in box under dash, under hood, checked relays that i could find. it runs like timming is off or miss firing. please help
Is the check engine light ever coming on?