octane ?
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
the PCM will only use the low octane tables if it detects extended periods of knock... the PCM is reactive not pro-active ... it doesn't know what octane you put in .. it only corrects when it detects knock/detonation/pre-ignition ... and by that time ... if it's bad enough ... could be too late
if it detects engine knock... it will work its way towards the low octane tables (I believe that it averages the two tables for a period but not 100% confident... I am pretty sure it's not cut and dry use high or use low octane tables though)
if you want to tune a car for 87 octane then I would modify the high octane... tables keeping them above the values in low octane ... that's the only pro-active way to handle it...
if it detects engine knock... it will work its way towards the low octane tables (I believe that it averages the two tables for a period but not 100% confident... I am pretty sure it's not cut and dry use high or use low octane tables though)
if you want to tune a car for 87 octane then I would modify the high octane... tables keeping them above the values in low octane ... that's the only pro-active way to handle it...
