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Hi, using Uprev on a Nissan Engine. The Base Fuel Schedule in ms when under load at WOT peaks 19ms at about 4000rpm with MAF at about 3.8v and then drops as RPM increases, until at 6000rpm it reads 16ms and MAF says 4.2v
Am I correct in thinking I need to tweek my MAF table at the high end?
Might be a silly question, or two, but...
Injector duty cycle peaked at 4k and dropped through 6k? MAF voltage increases with rpm as it increases with airflow as it is a constant current type (some are the other way round, so checking)?
If so, and you are confused why it seems to need less fuel with an increase in air flow, it is because the total fuel used by the engine is a result of pulse width * number of cylinders/2 * rpm whereas the airflow just increases. This means that the engine is actually burning more fuel, to match the increase in air mass, despite less fuel and air being consumed by each cylinder per revolution. Less is being consumed, or if you prefer volumetric efficiency drops off, because the cylinder filling is less efficient.
As a rough guide, the duty cycle of the injectors, and the air drawn in by each cylinder, will follow the torque curve of the engine and, if it varies much from that you have a problem somewhere.
Yes, increased to peak at 4k then drops, I am not sure which type it is,
Ahh, so base fuel schedule is like fuel per revolution, not like total consumed over time? Then is normal and I should not worry about it. Thanks
If I understand your question correctly - anyone else?
Oh, and it is a NA engine?
Yes NA engine
Generally the injector pulse width will follow the shape of the torque curve. Torque essentially represents airflow into the engine. Think of it like this - At peak torque we have maximum airflow into a cylinder and hence to maintain a given air fuel ratio we also need maximum flow from our injector. As we move past peak torque the VE drops off and hence we need less fuel to maintain that same air fuel ratio. So it should then make sense that our injector pulse width is maximum around peak torque and then drops off. The tricky part is that injector pulse width is NOT the same as injector duty cycle. To get duty cycle we also need to consider cycle time (how long a complete engine cycle takes) and this reduces as engine rpm rises. So typically what you should see if you log pulse width is a curve that closely follows your torque, BUT the injector duty cycle will closely follow the power curve.
Think of the "base fuel schedule" as proportional to VE.