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OBD Scanners Discussions on using On Board Diagnostic (OBD) scanners/ Diagnostic Equipment related to TDIs

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Old May 5th, 2007, 03:18   #1
leoncupra
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Join Date: Apr 2007
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Default air mass

according to ross tech measuring blocks - general engine data, there are vehicle with air mass sensor and vehicle with boost pressure.
But I am sure that also tdi ang gasoline turbos have air mass, or how would ECU then know the air mass?
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Old May 5th, 2007, 06:35   #2
Sebastian
 
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These are not boost pressure sensors, but these are intake manifold pressure sensors. Based on that and the temperature the ECU calculates the mass air flow.
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Old May 5th, 2007, 16:20   #3
leoncupra
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yes now I know that there are different methods to measure air mass, with hot vire sensor (electrical resistance measurment) and intake temp and once that calculate air flow, temp and pressure and thus calculating density and mass.
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Old May 8th, 2007, 20:34   #4
GoFaster
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Most vehicles nowadays, including TDI, measure BOTH the air mass flow rate and the temperature/pressure of the intake air. In the case of the TDI, the information is not redundant, because the difference between the two is the amount of EGR (exhaust gas recirculation) that is being used, since the EGR quantity cannot be directly measured.
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Old May 9th, 2007, 17:44   #5
leoncupra
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Quote:
Originally Posted by GoFaster
Most vehicles nowadays, including TDI, measure BOTH the air mass flow rate and the temperature/pressure of the intake air. In the case of the TDI, the information is not redundant, because the difference between the two is the amount of EGR (exhaust gas recirculation) that is being used, since the EGR quantity cannot be directly measured.
air mass sensor consist of temp sensor and hot wire that change its electrical resistance with temp. So for ECU to calculate air mass flow it needs temp data and wire resistance data. But yes engines have also pressure sensor, because TDIs have turbo and have to monitor boost pressue.

EGR valve is controled on the base of O2 readings.
EGR in diesel is because diesel engines have no throttle valve and thus operate on too "lean" mixture. With some exhaust gas recirculation (up to 60%) the engine lowers NOx emissions.
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