Yeah, in this case "BLM" does not mean "Burn, Loot, Murder". It's Block Learn Multiplier, but I prefer just "Block Learn" or "long-term fuel trim".
The short-term fuel trim is "Integrator". Why GM chose those names is beyond my pay-grade.
TBI problems, running rich
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The short-term fuel trim is "Integrator". Why GM chose those names is beyond my pay-grade.
thegawd
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well, If I never read those last 2 post, I would not have a clue what your talking about! LMAO
I kind of understand the short term and long term fuel trims, somewhat anyways so now I'm up to speed? kind of. lol.
I kind of understand the short term and long term fuel trims, somewhat anyways so now I'm up to speed? kind of. lol.
Yeah, the Integrator is a mystery to me too. Here's a couple definitions which don't really help either, ha ha.
INT = The short term fuel trim value is called the Integrator The value of the integrator varies above and below 128 with 128 being no correction. For example, if the Integrator is 135, the ECM is adding fuel because the 02 sensor is reading a lean mixture. If the Integrator is 110, the ECM is removing fuel because the 02 sensor is reading a rich mixture. Anytime the system is not in closed loop, the Integrator will immediately return to a value of 128 and stay there.
BLM = Block Learn Multiplier. Block Learn Mode term is long term fuel trim. BLM value tracks the Integrator but has a delay. If the Integrator increases so does the BLM, but the BLM lags behind the Integrator. The higher the Integrator climbs above 128, the faster the BLM rises. BLM value affects the VE table by adding fuel above 128 and subtracting fuel below 128
Enjoy!
All you really need to know is that the computer is adapting to the signal received from the O2 sensor. It's modifying the open-loop fueling tables programmed-into the PROM because the O2 sensor is functioning but unhappy.
Modifying the fueling tables is really the only purpose of the upstream O2 sensor(s). The whole point of having one or more upstream O2 sensors is so the computer has data available to make better decisions about the amount of fuel to spray. This provides minimum NOx emissions while maintaining "adequate" fuel economy. As the O2 sensor ages, it's response slows. The computer does not get accurate data, and the fuel trims go farther away from what they should be.
(Fuel economy could be increased by running the mixture leaner than 14.7-ish at light load--but NOx increases and that's more evil to our Government than burning extra gasoline. I think the Government is nuts, but who am I to fix all that's wrong with the hateful and deceitful EPA, not to mention the three main branches? GM knows this, they have a "Highway Lean Cruise" feature installed on vehicles exported to countries that don't have stringent NOx emissions regulations.)
Modifying the fueling tables is really the only purpose of the upstream O2 sensor(s). The whole point of having one or more upstream O2 sensors is so the computer has data available to make better decisions about the amount of fuel to spray. This provides minimum NOx emissions while maintaining "adequate" fuel economy. As the O2 sensor ages, it's response slows. The computer does not get accurate data, and the fuel trims go farther away from what they should be.
(Fuel economy could be increased by running the mixture leaner than 14.7-ish at light load--but NOx increases and that's more evil to our Government than burning extra gasoline. I think the Government is nuts, but who am I to fix all that's wrong with the hateful and deceitful EPA, not to mention the three main branches? GM knows this, they have a "Highway Lean Cruise" feature installed on vehicles exported to countries that don't have stringent NOx emissions regulations.)
It takes the VE (Volumetric Efficiency) tables and adjusts from its cells to maintain Stoich, or as close as it can and keeps it in RAM, it does not actually modify the tables so, if you disconnect the battery you'll reset the RAM and start over with the original tables. That's why you want a "tune" when you modify any components in the engine - to get your VE table as close as you can to start with.
And advance the timing too for better efficiency. I'm running ~16.5 AFR and ~42* advanced in HLC based upon MAP values.
It's still in a lot of their calibrations but they have it disabled. The same with EGR too.
You said it better than I did.
I think I learned about HLC from you. Thanks for that.
I've been thinking about this term and I have a theory where it comes from. I just kept forgetting to post it, ha ha.
Integrator may come from the process control P.I.D. - Proportional Integral Derivative where GM is only using the Integral portion of the entire loop, thus the name Integrator where, the further the value moves from the target, it adjusts its parameter accordingly. In this case it's duration of injector spray - maybe?
From Wikipedia (PID Controller), which helps to explain why you get O2 sensor cross counts - maybe? 
Applying too much integral when the error is small and decreasing will lead to overshoot. After overshooting, if the controller were to apply a large correction in the opposite direction and repeatedly overshoot the desired position, the output would oscillate around the setpoint in either a constant, growing, or decaying sinusoid. If the amplitude of the oscillations increases with time, the system is unstable. If they decrease, the system is stable. If the oscillations remain at a constant magnitude, the system is marginally stable.
Integral
An integral term increases action in relation not only to the error but also the time for which it has persisted. So, if the applied force is not enough to bring the error to zero, this force will be increased as time passes. A pure "I" controller could bring the error to zero, but it would be both slow reacting at the start (because the action would be small at the beginning, depending on time to get significant) and brutal at the end (the action increases as long as the error is positive, even if the error has started to approach zero).Applying too much integral when the error is small and decreasing will lead to overshoot. After overshooting, if the controller were to apply a large correction in the opposite direction and repeatedly overshoot the desired position, the output would oscillate around the setpoint in either a constant, growing, or decaying sinusoid. If the amplitude of the oscillations increases with time, the system is unstable. If they decrease, the system is stable. If the oscillations remain at a constant magnitude, the system is marginally stable.
I apologize if taking this down the geek rabbit hole - but you started it!
I know a bit about control systems - ie. things that use feedback of something to control something to a target. eg. missile targeting, cruise control, and I assume this feedback loop controlling the TBI AFR.
You're right about the source of the terminology. Control systems can be of different "order" which means they use more info from the feedback signal(s). You can control something just with the difference between target and actual. You can do better controlling something with the difference between target and actual + the rate of change. You could also incorporate the 2nd derivative for even better performance.
A first order control system uses the first derivative of the signal. In a control system, this means the system contains an integrator (essentially the math which does the derivative and determines the correction needed).
The BLM block learn multiplier is not familiar to me but a "block diagram" is used as term to describe a control system diagram/design. So I'd guess the BLM is the steady state error or offset correction needed for the various AFR control cells. For example, the steady state fuel requirements @ high RPM/cruising is larger than at idle. When control system changes cells it uses that steady state value as "center point" and then zeros in to target A/F - seems like by watching Int and if it rails tweaking the BLM center. All this is a guess but how I think about the system.
a bit technical but may be interesting https://www.electrical4u.com/first-order-control-system/
from that article:
In a closed-loop control system, the system has the ability to check how far the actual output deviates from the desired output (as the time approaches infinity, this difference is known as the steady state error). It passes this difference as feedback to the controller who controls the system. The controller will adjust its control of the system based on this feedback.
..... We have two types of systems, first-order system, and second-order system, which are representative of many physical systems.
The first order of the system is defined as the first derivative with respect to time and the second-order of the system is the second derivative with respect to time.
A first-order system is a system that has one integrator. As the number of orders increases, the number of integrators in a system also increases. Mathematically, it is the first derivative of a given function with respect to time.
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