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The Dr. usually hangs in the performance BB.
Yes, the T5 runs open loop, because when on boost the mixture is quite rich to prevent knocking. The rich condition cannot be resolved by the O2 sensor as the mixture is outside of its band of resolution.
Your concern about the about how the mixture then might be affected by modifying the exhaust is a good question. That can change the volumetric efficiency and change the amount of air getting into the cylinders for a given manifold pressure and RPM.
The ECU monitors the AF mixture when off boost where the closed loop functions are in use. It creates parameters which take into account the volumetric efficiency, the intake air pressure, temperature, humidity, fuel energy content and fuel temperature, and fuel pressure. Some of these things change quite quickly compared to others. These parameters are still in effect when in open loop mode. So the ECU needs only to keep the injectors open a percent longer to get an enriched mixture.
So a change in the exhaust system would be parmetrically accomodated during closed loop operation. Dr. Boost did state that if the engine were rebuilt and oversized pistons were fitten, that the ECU would handle everthing fine. That is a change in volumetric efficienty from the ECU's point of view. Installing a different turbo would affect back pressure and V.E. as well.
So that is the general idea in vague terms. I am sure that the actual hard facts would be very interesting. There might even be a knock sensing parameters that drive the enrichment as well.
I suspect that in the T5's that there is a temperature where the ECU chickens out get sets the timing less agressively. Thats just how it feels to me in the summer. At certain temperatures the power loss seems very non linear. Insulation of some intake components helps to avoid some of this power loss.
posted by 208.24.179...
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