Thread: ECU Octane switch

Knock sensors tell the PCM how much knock you are getting, PCM then adjusts which timing table you are on.

just run 93, dreamers.......

Originally Posted by Scottydoggs

just run 93, dreamers.......

This.

Currently 87 is 2.49 and 93 is 2.79.

If you need 15 gallons filling up with 87 will save you a whopping $4.50. Don't eat at McDonald's one day and put 93 in the tank if you are supercharged.

In addition...you'll live much longer. There's something wrong when fries taste that good and never change how they look after they fall under a seat for a year or two.

You really wanna meet Chip, don't you?

Originally Posted by owi racing

So stupid question, if I'm running 87 without any knock will the ecu run the timing from the high octane table? Also, if i'm making a WOT run and get a degree or two of knock will the ecu drop me down to the low octane table? If not how much knock does it take before the ECU implements a change in tables?

You would need to probe deep into the pcm and talk to the programmers to know this.

i dont know if anyone knows that actually algorithm that the PCm uses to calculate the changes but it is known that the PCM does blend the tables based on history. disconnecting the battery lets the pcm loose the memory of what it was doing with the tables. doing a write on the PCM does the same thing. the information is never hard written to any memory in the PCM.

Unplugging the battery is a way to force the fuel trims to relearn, doing a partial pcm write will not do this unless you check the box for reset fuel trims? I don't believe the timing tables themselves do learn or adapt, there are tables that adjust the timing based on other conditions on the fly. The fuel trims would adjust to some extent if there was a fuel change, other tables may be slightly adjusted because of that. It usually takes 20-30 minutes of various driving to get the fuel trims to re-learn after you do a reset. I would be absolutely sure you aren't getting knock, you need to be logging.