Octane requirements
I guess I should have been more specific;
Sorry man, this was not directed to any one in particular, I just saw the way the thread was going, lol. and put my 2cents in .......
=============================================================
by the way, as to your truck; This is how I learned EFI, your truck may not be exactly like this, but you get the idea;
the ECU pulls timing in steps, the first time it senses a knock event. It will continue to pull timing until the knock quits. Then, as time goes by, it puts it back. Meanwhile, you sense the crappy running.
The Ecu keeps track of how much timing it pulled. This is a short term compensation.The next time you start it up, the ECU trys to nurse the timing back up. But if you are still running the lower-octane, and it gets back into detonating, it pulls the timing out again. Now it has a long-term history.
IIRC, it takes three, short term events to send the ECU into a long-term correction.
After that, each time you start it, she will run on the long-term correction, for the next three consecutive cold-starts. On the Fourth cold-start, it will start bringing the timing back. If you have, in the mean time, gone back to adequate-octane gas, she will start building a new timing curve. If you are still running too low an octane, it will go back to square one.
You can short circuit this learning process by disconnecting the battery, for IDK how long, which will restore the ECU to factory defaults. From there, the ECU jumps past all the tom-foolery. However, when you do this, the Fuel corrections are also erased ...... so she will be hard on gas until the ECU has dialed it back.
You gotta remember, that the ECU is trying to protect your engine from killing itself thru detonation. Your engine has a different octane requirement for every load-setting and rpm. At cruising in steady state, with the throttle relatively fixed, it's EFFECTIVE compression ratio might be 5/1 or less and she might be happy with the crappiest gas money can buy. But that poor engine still has to get the 5 or more thousand pound rig up to speed, and that might take best gas, depending on in how much of a hurry you are. Once the timing has been pulled, it only comes back in small steps over a longer time period. And that is likely what you sensed.
The octane of the fuel is fixed, so the fuel you use has to be able to keep calm under the highest load. Which means, for most of us, 95% of the time, we are wasting our gas-dollars on hi-test. That's just the way it has to be.
If you want to see your ECU in action, get yourself a scanner with graphing ability. Then call up timing and MAP on the graph. Now you can see the correlation of timing to load, that the computer is running on. Maybe you can pinpoint under what circumstance the ECU pulls the timing, and avoid that situation. You can also see how much timing it restores and how long it takes to recover. If you can figure it out, maybe you can run a lower-grade fuel all the time and save some coin at the pumps. Well,
with a hemi,
maybe not, lol.
