TMAPS and MAF and ECU
08-02-2013, 02:24 PM
#1
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TMAPS and MAF and ECU
Why does this ECU need an MAF and 2 MAP sensors? How does the ECU use them? are they just for redundancy/error checking?
I unfortunately do not have the FSM yet. I am curious why this ECU needs to read the incoming air flow from so many locations.
I unfortunately do not have the FSM yet. I am curious why this ECU needs to read the incoming air flow from so many locations.
08-02-2013, 04:39 PM
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OK, here goes..
The Mass Air Flow (MAF) sensor is integrated with the Intake Air Temperature (IAT) sensor. The MAF sensor is an air flow meter that measures the amount of air entering the engine. The Engine Control Module (ECM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF/IAT sensor has the following circuits:
* An ignition 1 voltage circuit
* A ground circuit
* A MAF sensor signal circuit
* An IAT sensor signal circuit
* A low reference circuit
The ECM applies 5 volts to the MAF sensor on the MAF sensor signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies in a range of near 1,700 Hertz at idle to near 9,500 Hertz at maximum engine load.
Now for the MAP sensors....
The Manifold Absolute Pressure (MAP) sensors measure the pressure inside the intake manifold. Pressure in the intake manifold is affected by engine speed, throttle opening, air temperature, and Barometric Pressure (BARO). A diaphragm within the MAP sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The MAP sensor wiring includes 3 circuits. The Engine Control Module (ECM) supplies a regulated 5 volts to the sensor on a 5 volt reference circuit. The ECM supplies a ground on a low reference circuit. The MAP sensor provides a signal voltage to the ECM, relative to the pressure changes, on the MAP sensor signal circuit. The ECM converts the signal voltage input to a pressure value.
Under normal operation the greatest pressure that can exist in the intake manifold is equal to BARO. This occurs when the vehicle is operated at Wide Open Throttle (WOT) or when the ignition is ON while the engine is OFF. Under these conditions, the ECM uses the MAP sensor to determine the current BARO. The least manifold pressure occurs when the vehicle is idling or decelerating. MAP can range from 10 kPa, when pressures are less, to as great as 104 kPa, depending on the current BARO. The ECM monitors the MAP sensor signal for pressure outside of the normal range.
Simple huh?
The second MAP sensor basically functions as redundant backup to the first.
The Mass Air Flow (MAF) sensor is integrated with the Intake Air Temperature (IAT) sensor. The MAF sensor is an air flow meter that measures the amount of air entering the engine. The Engine Control Module (ECM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF/IAT sensor has the following circuits:
* An ignition 1 voltage circuit
* A ground circuit
* A MAF sensor signal circuit
* An IAT sensor signal circuit
* A low reference circuit
The ECM applies 5 volts to the MAF sensor on the MAF sensor signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies in a range of near 1,700 Hertz at idle to near 9,500 Hertz at maximum engine load.
Now for the MAP sensors....
The Manifold Absolute Pressure (MAP) sensors measure the pressure inside the intake manifold. Pressure in the intake manifold is affected by engine speed, throttle opening, air temperature, and Barometric Pressure (BARO). A diaphragm within the MAP sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The MAP sensor wiring includes 3 circuits. The Engine Control Module (ECM) supplies a regulated 5 volts to the sensor on a 5 volt reference circuit. The ECM supplies a ground on a low reference circuit. The MAP sensor provides a signal voltage to the ECM, relative to the pressure changes, on the MAP sensor signal circuit. The ECM converts the signal voltage input to a pressure value.
Under normal operation the greatest pressure that can exist in the intake manifold is equal to BARO. This occurs when the vehicle is operated at Wide Open Throttle (WOT) or when the ignition is ON while the engine is OFF. Under these conditions, the ECM uses the MAP sensor to determine the current BARO. The least manifold pressure occurs when the vehicle is idling or decelerating. MAP can range from 10 kPa, when pressures are less, to as great as 104 kPa, depending on the current BARO. The ECM monitors the MAP sensor signal for pressure outside of the normal range.
Simple huh?
The second MAP sensor basically functions as redundant backup to the first.
exactly what I was gonna say.
08-02-2013, 07:35 PM
#6
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843de while I appreciate your explanation, it dont believe it answers the original question.
Why does the ECU need both. The MAF is a better sensor to use to measure incoming oxygen based on the resistance changeing across the element. It can hand changes in volume, temperature, pressure etc..
So if the MAF is the primary source for fuel delivery, then what are the MAP sensors for? MAP sensors are less accurate than MAF because they cant account for changes in VE. MAF does not have this issue provided you dont exceed its max voltage.
This question is born out of the frustration of dealing with the lower TMAP sensor.
Why does the ECU need both. The MAF is a better sensor to use to measure incoming oxygen based on the resistance changeing across the element. It can hand changes in volume, temperature, pressure etc..
So if the MAF is the primary source for fuel delivery, then what are the MAP sensors for? MAP sensors are less accurate than MAF because they cant account for changes in VE. MAF does not have this issue provided you dont exceed its max voltage.
This question is born out of the frustration of dealing with the lower TMAP sensor.
08-02-2013, 07:49 PM
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To put it bluntly, the ECM requires but MAF and MAP inputs because that's the way it was designed. You'd really need to address your question with an engineer at GM's powertrain design and engineering section.
The MAF/MAP combo is a "belts & braces" approach to fuel management, it's going out of style and many newer GM engine control systems use MAF's only.
You're stuck with the TMAP unless you find someone with the knowledge and wherewithal to create a reflash for the ECM, or create a MAP emulator to feed the ECM with a signal that it will accept in place of those generated by the MAP's.
The MAF/MAP combo is a "belts & braces" approach to fuel management, it's going out of style and many newer GM engine control systems use MAF's only.
You're stuck with the TMAP unless you find someone with the knowledge and wherewithal to create a reflash for the ECM, or create a MAP emulator to feed the ECM with a signal that it will accept in place of those generated by the MAP's.
08-02-2013, 08:35 PM
#8
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If I knew any engineers at GM I would love to pick their brains.
Thanks for the reply. Ive worked/tuned quite a few german and japanese cars, but this is my first GM. Also the first car ive owned that uses both MAP and MAF together.
Thanks for the reply. Ive worked/tuned quite a few german and japanese cars, but this is my first GM. Also the first car ive owned that uses both MAP and MAF together.
08-02-2013, 11:49 PM
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Thanks for jarring my memory.
