Quote:
Originally Posted by Blueclyde
Back to the issue of spark tables and "clearing" the ECM. Most current automotive controls systems employ what is called "Adaptive" control strategy. The primary purpose of this strategy is to allow the engine controller to learn and re-adjust as the engine/vehicle goes through its normal use/wear life cycle. This strategy is one of the ways that the auto companies insure their vehicles comply with the EPA & CARB emission useful life periods legislated for on-highway vehicles (no trivial task here). This is nothing really new. This has been around for a while. One point that I would like to make is that these systems general learn bi-directionally. Meaning, if an engine subsystem has a problem (like a plugged air filter), the system will adapt to that. Once a problem is corrected the system will adapt back. Yes, resetting adaptive parameters back to zero (or "clearing" the ECM) will generally speed that process up, but it will also occur on its own over the course of normal vehicle operation.
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The adaptive corrections SHOULD occur. But in a large number of the L99's, it hasn't been occurring. I agree that pulling the fuses is kind of a "hack" but the only way to truly correct it is through a ECU update from GM which we have no control over. Pulling the fuse and getting it to work with minimal effort essentially takes the ECU to factory defaults...I don't see a problem with that, especially since you won't have to do it again as long as you keep premium gas in the tank.
Quote:
Originally Posted by Blueclyde
With respect to spark calibration tables and "93 Octane Tables" and "87 Octane Tables" I would be very surprised to find more than one spark calibration table in the control strategy. Again, I am no expert on the GM controller but I would be surprised if there are multiple tables. Generally there is one spark table that is calibrated across the speed and load range using the recommended fuel. I would think in this case with this being a performance vehicle the base spark calibration was done with high octane fuel. This engine is equipped with a knock sensor that is calibrated to detect and report occurrences of spark knock back to the engine controller. "Generally" engine control strategies use this knock sensor input data to "derate" or pull back spark advance from the base spark table. Calibrations are created to pull back the appropriate amount of spark for the input signal received from the knock sensor. There are probably other sensor based spark derate systems employed in addition to knock. Parameters such as intake air temperature and engine coolant temperature probably also have spark derates associated with them. If this is in fact the case, then none of this makes any sense, unless there are also other fueling corrections being made when the spark is being pulled out.
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There ARE two tables (See screenshots below). There is spark derating that occurs in real time to correct for knock in certain cells WITHOUT the ECU giving up and going directly to the low octane table...This is known as knock retard - and is an "adaptive" set of values...but if it sees TOO much knock from the knock sensors it reverts to the low octane table.
Think of the high octane and low octane tables as a coarse adjustment to "get it in the ballpark" and the knock retard as a fine tuning adjustment...
These screenshots are from a 2002 Z28 factory default configuration...1st screenshot is the Spark Advance Menu, 2nd screenshot is the High Octane Table, and 3rd screenshot is the Low Octane Table. Notice the BIG differences between the two tables occur at WOT (the values at the bottom of each screenshot)
THAT IS WHY THIS WORKS!!!