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The trionic ECU's are identified by a 'T' and an number. The NG900's use ath T5 ECU.
The T5 ECU is a 'speed density' control system which calulates air flow by pressure with an absolute pressure transducer, a temperature sensor and by engine rpms. The T5 controls the boost pressure. Too much pressure, and the ECU stops firing the fuel injectors while the pressure boost pressure signal is high. Everything then returns to normal. This is called fuel cut.
The T7 uses an air mass meter, which creates a signal which is proportional to the air mass flow as the name suggests. The ECU can calculate the required fuel flow requirements from this signal alone. However, when on boost, the mixture will be made richer than the air mass signal would imply.
All turbo systems run rich while on boost to avoid destructive engine knock. A lean mixture if fatal on boost. Higher air temperatures will probably also dictate richer mixures. The ignition timing is retarded while on boost or with hot intake air.
An standard air mass flow metered turbo system will have a pressure sensor to implement a fuel cut. That pressure sensor is not doing very much can can be implemented by a pressure switch. But pressure switches measure guage pressure and not absolute pressure. So an absolute pressure sensor will provide more power at altitude in the mountains.
The latest T7s, starting with the introduction of the Viggens do not have a boost presure fuel cut, because the control point is a level of air mass flow which translates to a given level of torque. This means you get the same power in the mountains with thinner air... up to a certain point. The T7's have a soft fuel cut, if you fake out the boost with a MBC, the ECU can alter the fly by wire electic throttle to reduce the air mass flow that way. Tricky little beastie. The boost indicator on a T7 shows a signal proportional to air mass flow, not boost pressure.
More than you wanted to know.
posted by 208.24.17...
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