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Discussion Starter · #1 ·
O.k., I've been thinking about oxygen sensors and how the ECU uses this information to control the gas mixture. The airflow into the engine is nicely sensed by the MAF (mass air flow) sensor using a hot wire system. The residual oxygen in the exhaust is measured by the O2 sensor and tells the ECU to increase or decrease the air-fuel ratio (normally about 14:1 for gasoline). This is usually under acceleration (closed loop mode). Internal air-fuel maps in the ECU are designed for optimal performance based on known fuel, engine and sensor characteristics. Modern ECUs can partially adapt to a range of fuels and driving conditions.

Here's the rub, I noticed that Softronic was warning about problems using performance headers on the new DFI (direct fuel injection) engines. It occurred to me that the O2 sensors are not very accurate and only measure the relative concentration in the exhaust gas. Increased exhaust back pressure will probably raise this measurement even though the total oxygen flow out of the engine remains constant. Free flow headers will lower back pressure and cause an apparent drop in the O2 level. In turn, the ECU "sees" less O2 in the exhaust and tends to lean the fuel mixture under acceleration.

It seems what is called for is a total oxygen sensor which is pressure insensitive or a exhaust pressure sensor used in combination to effect the same thing. This is the only reason I can imagine that would cause the addition of free flow headers to actually reduce HP with a performance ECU flash. If the ECU is calibrated for a certain back pressure and O2 sensor response, then any change in the setup could confound an altered air-fuel mapping. Why DFI is more susceptible to this than the older PFI (port fuel injection) is unknown to me. I've heard that DFI can more accurately control the air-fuel mixture for better combustion and efficiency.

Any comments?
 

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Crusin worlds most isolated city
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I will get some A/F ratio data in stock form and after exhaust install tomorrow and well see if there is any change.
The only thing Im suspecting is the DFI is more optimized for fuel economy and CO2 emissions and so its less forgiving when something changes.
 

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Discussion Starter · #3 ·
What is really need is the ability to code up a statistical estimator of the parameters of some high order model of the "system". I think this approach is known as Kalman filtering. In this way all the constants of the system regarding fuel and sensor characteristics could be determined according to an optimal criterion. This would lead to a very accurate parameterization for any driving/fuel setup and should improve performance over a broad range of driving conditions. Sorry to be so technical.
 

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On Probation
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install a wideband kit
 

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Discussion Starter · #5 ·
What's that?
 
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