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The Radium King · 12-17-2014, 07:22 AM

it would be interesting. when under partial load, the computer tries to maintain a ratio of air to fuel of 14.7. the o2 sensors in the exhaust monitor this and are constantly correcting fuel delivery to match apparent air intake. these corrections get turned into fuel trims. so, fuel pressure and flow rate is a moot point during this closed loop operation, as the computer would adapt to the changes (up until the point when the fuel trims reach 20%, at which point you get an error code). of course, this won't address one bad injector, as the sensors monitor a bank of three cylinders each (computer can detect bad electrics on a single injector, however).

when the engine is at full load the computer adds a bit more gas (tries to maintain an air fuel ratio of approximately 12.5) to keep things cool and reduce detonation. the narrow band o2 sensors don't work at this mixture however, so the computer gets no feedback and operates open loop. basically, it looks at incoming air and applies what it thinks is an appropriate amount of fuel based on pre-programmed air/fuel/rpm maps. fuel pressure and injector flow become important at these high flow conditions, as the computer is getting no feedback on whether target fuel delivery is being met. worst case is that there is insufficient fuel flow during max flow requirements, resulting in a higher air to fuel ratio, engine runs hotter without the quenching from the additional fuel, and damage could occur (or computer detects detonation and throttles back operation). of course, reduced fuel flow also draws the air fuel mixture closer to the magic 14.7 ratio, increases power, and increases fuel efficiency. so, you may not want more fuel pressure ...

I don't think intake/exhaust mods will have much effect on the fuel delivery system, even at full load, as the computer is still monitoring the amount of air ingested. as long as the increase in airflow does not exceed the sensing ability of the maf or the data available in the maps things should be ok - again, as long as there is sufficient fuel pressure and flow available in the system. given that the same maf, fpr and injectors are used in the 3.4 L 996 making 300 hp stock, and that the computer has the ability to adjust up/down by 20%, I would presume that they are.

12-17-2014, 07:22 AM	#8
The Radium King Registered User Join Date: Apr 2010 Location: Canada Posts: 3,121	it would be interesting. when under partial load, the computer tries to maintain a ratio of air to fuel of 14.7. the o2 sensors in the exhaust monitor this and are constantly correcting fuel delivery to match apparent air intake. these corrections get turned into fuel trims. so, fuel pressure and flow rate is a moot point during this closed loop operation, as the computer would adapt to the changes (up until the point when the fuel trims reach 20%, at which point you get an error code). of course, this won't address one bad injector, as the sensors monitor a bank of three cylinders each (computer can detect bad electrics on a single injector, however). when the engine is at full load the computer adds a bit more gas (tries to maintain an air fuel ratio of approximately 12.5) to keep things cool and reduce detonation. the narrow band o2 sensors don't work at this mixture however, so the computer gets no feedback and operates open loop. basically, it looks at incoming air and applies what it thinks is an appropriate amount of fuel based on pre-programmed air/fuel/rpm maps. fuel pressure and injector flow become important at these high flow conditions, as the computer is getting no feedback on whether target fuel delivery is being met. worst case is that there is insufficient fuel flow during max flow requirements, resulting in a higher air to fuel ratio, engine runs hotter without the quenching from the additional fuel, and damage could occur (or computer detects detonation and throttles back operation). of course, reduced fuel flow also draws the air fuel mixture closer to the magic 14.7 ratio, increases power, and increases fuel efficiency. so, you may not want more fuel pressure ... I don't think intake/exhaust mods will have much effect on the fuel delivery system, even at full load, as the computer is still monitoring the amount of air ingested. as long as the increase in airflow does not exceed the sensing ability of the maf or the data available in the maps things should be ok - again, as long as there is sufficient fuel pressure and flow available in the system. given that the same maf, fpr and injectors are used in the 3.4 L 996 making 300 hp stock, and that the computer has the ability to adjust up/down by 20%, I would presume that they are.