Heres some reading i pulled from the net:..TIM Print
2. Does it take several hundred miles of driving to "learn in" the computer? Does the computer learn everything about the way I drive?
No. The ECM contains two things responsible for learning - a short term memory called the Integrator (INT) or Closed Loop Correction term (CLC), and a long term memory called the Block Learn Memory (BLM). The only thing that is stored and memorized is the BLM. There are 16 BLM cells numbered 0-15, separated into a grid by RPM and Mass Air Flow (MAF). As you rev the engine you "travel" through the BLM grid and hit various cells. 0 is the idle cell and 15 is the WOT cell. The BLM cell number is not a part of the serial data stream (in the SFI-M Turbo Buick ECMs) so scan tools are not able to indicate which BLM cell you’re in. They will however, give the value of the current BLM cell.
The O2 sensor will detect a rich/lean condition, and cause the INT to change. The BLM is simply a long term average of the INT. 128 is a normal number, signaling no change. A number greater than (>) 128 reflects a lean condition, and a number less than (<) 128 reflects a rich condition. Put another way, a number greater than 128 indicates the ECM is adding more fuel (going, or learning richer) to compensate for a lean condition, and a number less than 128 indicates the ECM is taking away fuel (going, or learning leaner) to compensate for a rich condition. The more we deviate from 128, the more correction the ECM is learning, and hence the worse the base cal is for that given condition.
Only the BLM is saved and memorized. The INT resets on start-up and is constantly changing. By clearing the ECM memory the BLMs are reset to 128. BLMs are the ONLY thing the ECM memorizes and are totally related to how the O2 sensor detects the fueling to be, thus the ECM does not learn or detect things such as driving habits. The O2 sensor considers a stochiometric air-fuel ratio (AF) of 14.7:1 to be optimum.
3. What are "good" BLM numbers to see? How far can the ECM compensate?
Generally, if the base open loop cal is correct for the size injectors used and compensated accordingly for the flow characteristics, BLM should not deviate more than 10 points on either side of 128. This means you shouldn’t see numbers much beyond a range of 118-138, and the majority of cells should range more within 121-135. Remember that fuel pressure (FP) GREATLY affects the BLM values, and a deviation of 1 psi can throw BLMs off by a few points! If you see the majority of BLM numbers skewed in one direction, a slight tweak in FP may be warranted. Weather conditions affect BLMs drastically too, and this is precisely why they exist, and why closed loop operation with the ability to learn is preferable for part throttle driveability.
The factory calibration limited BLMs from 110 to 150, which is more than enough to compensate from any aging effects or weather conditions. In fact, it is due to this wide learning capability that some folks can passably run blue top injectors on a chip made for stock injectors, as the BLMs simply compensate for the incorrect base cal. The BLMs have limits because if a sensor malfunctioned, forcing BLMs to incorrectly skew one way or another, you’ll want to limit their authority somewhat so that the engine would still run somewhat decently. Most aftermarket manufacturers have widened this authority to 90-160. We can only guess why they’ve done this - it makes for a more forgiving calibration, as you can have the base calibration deviate from the optimum by a much larger amount and the ECM will still be able to compensate.
4. I’ve been told that I should drive fast and accelerate hard to learn in the computer.
No. By always accelerating hard you’ll never learn in the computer. This is because you’ll be in Power Enrichment (PE) mode. Once you’re in PE, Learn-mode is turned off. About 10 minutes of normal, easy driving in stop & go traffic is sufficient to learn in the majority of the BLM cells.
5. What is Power Enrichment (PE) mode? How do I know I’m in PE mode?
PE mode is where additional fueling is given to run a richer AF mixture than stochiometric. The system remains in a "Closed Loop" mode but ignores the O2 sensor, essentially running "open loop" under a "Closed Loop" mode for lack of a better term. On a scan tool, the "Closed Loop Mode" indicator will still indicate closed loop, however, the INT will be reset to 128 and Learn-mode will be off. The BLM value displayed will be the value used in the fueling calculations, and will usually, but not always, reflect BLM cell 15 (depending on RPM and MAF). It is the last value learned in before entering PE.
6. What does it take to enter PE mode? Do I need to set the Throttle Position Sensor (TPS) to read 4.8v at WOT? I've been told from what I believe to be reliable sources that it took a MAF reading of 255 and TPS of 4.8 volts or so to enable PE mode.
That is an old wive's tale that's been propagated through the years and has unfortunately been taken as gospel. We believe we know how that rumour got started, but we won't go into that now! PE mode is actually entered quite easily. A certain throttle position is required based on RPM and a certain load must be reached, or given enough TPS, PE will enable regardless of RPM or load. Basically, about 20% TPS is needed to enter PE under most conditions.
The subject of max TPS reading is a sticky one, as there are folks that are convinced that they have seen an increase in performance by adjusting it higher. While we do not refute this, and can come up with some possible explanations as to why, these are the facts from the ECM software point of view:
For the 86-87 controller, there is no need to exceed 80% TPS in the stock chip. All PE fueling multipliers are identical after 75% and above, and for those of you racing with the AC on, the AC will shut off after 80% TPS. There is *nothing* in the cal that does anything beyond 80% TPS. For EFI Performance chips, there is no need to exceed 75% TPS.
Note that we are quoting values from the stock chip or ours. We have yet to see any other manufacturers raise these TPS boundaries, but it’s possible some may have, although we have no idea why anyone would. Note also these are percentage based, and we assume a 5v reference. If by some chance this reference was higher on a particular car, then the TPS voltage would have to rise too. We suspect this to be the reason some folks have successfully raised TPS voltage to achieve gains, if these gains could definitely be attributed to the increase in TPS alone.
7. OK, what is Closed Loop, Open Loop, and Learn mode?
On a cold start, the engine starts out in Open Loop. This means that there is no feedback mechanism (from the O2 sensor) in place, and the ECM is not correcting or learning to try to achieve a stochiometric AF ratio. It is simply running off some preset tables in the chip. A carburated engine, or any engine without an O2 sensor, operates in open loop mode.
On a cold start, we have to run quite rich as a cold engine will not vaporize fuel very well so additional fuel is thrown in to offset the small percentage that vaporizes and does work - ultimately, this extra fuel is wasted. This open loop cold start fueling is responsible for how well the engine operates cold. A correct calibration for the injector size and characteristics is important to achieve good seamless cold starts with a minimum of stumbles and hiccups. Factory engineers have an additional responsibility of meeting cold start emissions, which at times will hinder good driveability.
Closed loop operation occurs when the O2 sensor is used for feedback to adjust the AF ratio. Under most circumstances, when a preset coolant temp is reached and the O2 sensor heats up sufficiently to provide good signal, the ECM goes into closed loop mode, and the INT will begin to function. There is an additional coolant temp criteria that must be reached for Learn-mode to enable. This is when the BLMs begin to learn. Beta-tester Carl Ijames stated it particularly well - using a scan tool, "the Closed Loop flag is indicating that closed loop operation is now permitted but not necessarily in effect." Circumstances where closed loop is permitted but not in effect include PE mode and in the case of our chips, lean-cruise mode.
8. What good is the BLM during Open Loop, or PE mode? Are they being used or ignored? Learn mode is off under those conditions isn’t it?
Yes, Learn-mode is off during PE or Open Loop, but this only means that the ECM is not currently learning under existing conditions. However, whatever was previously stored in the BLM cell whenever Learn-mode was enabled is still being used! For example, if the BLM cell at 1500 RPM and 15 g/sec airflow learned to 130 under closed loop conditions, then 130 is still used to modify the fueling at that RPM/load point even under open loop or PE conditions. In other words, the stored values of the BLM cells are always in effect and will always affect fueling.
