Without going into extensive detail, I'm going to try and keep this short and to the point.
I recently came across a few posts that were regarding the whole Fuel Trim/Block Learn thing. What I found was somewhat hard to believe.
Some people have said that Block Learn numbers WILL decrease in a Speed Density system because as the engine gets hotter, the incoming air becomes less and less dense. Therefore, less fuel will be needed to maintain 14.7-1, and as a result, the BLM will decrease, as will the Injector On-Times.
Is this true!?
I find this hard to believe because up until today, I had never seen this mentioned whenever Fuel Trim is the topic? Also, from what I understand, the Block Learn figure is a direct result of the Integrator figure, which is a direct result of the Oxygen Sensor output(voltage). So, if the engine is measuring the "less dense" air as a result of inputs from the MAP, IAT, etc. BEFORE the result reaches the O2, would that not keep the A/F ratio at the proper amount, and therefore leave the Block Learn at or near the desired "128"?
I guess the point is this: If a Speed Density engine is supposed to be continuesly measuring the flow and density of incoming air, how can it affect the BLM numbers? BLM is supposed to be for correction only(based on O2), and is not used in the calculation of air flow and density. Maybe if the ECM was unable to monitor air density, I can see how it would make sense, but not in this situation.
I always thought that LOW Block Learn numbers meant an overly Rich running engine, am I supposed to now believe that this is not a problem or concern at all, and simply a reaction to the incoming airs temperature??
Anyone?