Originally Posted by crg914

Poor misguided souls. Resetting your PCM does nothing. NOTHING. It is an old wives tale. The PCM 'learns' certain mods by adjusting the fuel trims, short term and long term. This will happen regardless of whether you disconnect the battery and reset to PCM or not. It will not happen any sooner, or later. It takes drive cycles. There are 'blocks' for a certain load vs. rpm. The more time you spend in that 'block' the sooner the PCM learns and adjusts to it. It has adsolutely nothing to do with being reset.

People frequently get fooled into thinking it works because they reset the PCM, then they drive it like the stole it trying to get it to learn the new mod, and think that made a difference. In reality, if they just drove it like that anyway, the same thing would have happened.

People who reset their PCM have no understanding of the way a modern car and its monitoring systems operate.

Also, certain mods are able to be compensated for by the PCM and some are not. Depending on the manufacturer the fuel trims will either be +/- 15% or the baseline (read: 0) will be 128 and rich will be 129-255 and lean will be 0-127. Two ways of doing the same thing really.

The PCM can only compensate so much. For example, adding a new exhaust which will lean out the mixture will cause the fuel trims to go 'positive', which means adding fuel.

There is a limit though, that's why reflashes are still necessary after a while.

Don't mean to rant, just sick of always reading misinformation.