I think where the disconnect is, is your understanding of the fuel trims and adaptive fueling logic.
Having positive or negative fuel trims does not mean you are running rich or lean as you might think of it. You are still running at 14.6:1 AFR when in closed-loop. The trims are only an indication of how much the adaptive fueling routine had to adjust from your base fuel map (calibration values) in order to maintain 14.6:1 AFR. It would be extremely unusual for you to see zero fuel trims while driving. It is just the normal operation of the system.
The reality is there are always small differences in your actual fuel delivery, fuel combustion efficiency, combustion temperature, and atmospheric conditions that will result in deviations from what would be predicted by the main fuel calibration values that were programmed in at the factory.
If you change anything on your car, or the engine experiences normal aging and wear, the value of the fuel trims can increase.
Adaptive fueling keeps you at 14.6:1 AFR over the life of the vehicle as long as your O2 sensor is reporting properly.
If you start experiencing a problem with your engine running, then the fuel trims can be used in the troubleshooting process. For instance if your fuel trims are extremely high (maybe +25%) with your engine just idling, then that may be an indication of a vacuum leak.
A fuel trim of -25% at idle may indicate a fuel leak at the injector or a vacuum referenced fuel pressure regulator.
The variations on these possibilities to aid in troubleshooting are almost endless.
What you really want to do is monitor the commanded AFR from the PCM, and monitor actual AFR from a WBO2 sensor.
- Yes the MAP is very relevant in determining short-term fuel enrichment such as AE. Modulating the throttle slower will reduce the delta-MAP. This is what people have done for decades when driving while watching a vacuum gauge. Even with a carburetor, the reduction in throttle modulation requires less acceleration enrichment (pump-shot) and avoids activating the main power-valve system. With MPFI you have AE and PE that do the same enrichment jobs based on the same kind of throttle & vacuum input (how far and how fast on the pedal).
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Originally Posted by California98Civic
Olympiadis, I like the links you posted. If I understand, not intake restriction but EOC P&G itself might be contributing to a rich AFR in my car because of quick throttle position changes (from off to 9% to 25/26% quite suddenly). Such throttle positions are not nearly close enough to WOT for my 25% smaller diameter intake tube to restrict anything significantly, but the quick rate of change in the throttle position will trigger a brief, small, fuel enrichment. Interestingly, yesterday on the freeway my long term fuel trim returned to 0.00 after engine-on P&G for a while. During the neutral coasting glide phase, short term trim dropped into negatives. Apparently, the MAP sensor is mostly relevant because rapid changes in pressure contribute to the ECU's fuel enrichment response?
Sorry for apparently distracting this thread with the rich AFR issue. Thanks.
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