Thread: How to completely get rid of MAF on de-EGR'd TD5

Sorry but this is completely wrong.

The maf is to tell the ecu how much mass flow of air is entering the engine. Compensating for boost, temperature, altitude and weather.

Bypassing it is completely pointless.

Originally Posted by Dougal

Sorry but this is completely wrong.

The maf is to tell the ecu how much mass flow of air is entering the engine. Compensating for boost, temperature, altitude and weather.

Bypassing it is completely pointless.

Agreed...

i'm open for any friendly polemic on this believe me... your statement about the MAF is correct for other diesel and especially for petrol engines not for Td5, for temperature, altitude and weather there is the AAP sensor in the airbox, i made tests on the bench and the MAF disturbes the management only if it's faulty as open or short circuit or if it doesnt give the expected inputs, provided the EGR is bypassed, cos all the trouble which MAF can cause is when the EGR is still on and it's missmanaged by a faulty MAF(that's the gist of this, ... a lack of airflow will result in lack of boost sensed by the MAP or a depression sensed by the AAP which are responsible for fueling and boost controll, i quote the relevant parts from the book...but as i say this mod is tested live and working great ... the AAP and MAP/IAT sensors are important for Td5 management not the MAF if the EGR is bypassed

1. The MAF sensor is located in the intake system between the air filter housing and the turbocharger. The ECM uses
the information generated by the MAF to control exhaust gas recirculation (EGR).
The MAF sensor works on the hot film principal. The MAF sensor has 2 sensing elements contained within a film. One
element is controlled at ambient temperature e.g. 25 °C (77 °F) while the other is heated to 200 °C (392 °F) above
this temperature e.g. 225 °C (437 °F). As air passes through the MAF sensor the hot film will be cooled. The current
required to keep the constant 200 °C (392 °F) difference provides a precise although non-linear signal of the air drawn
into the engine. The MAF sensor sends a voltage between 0 and 5 volts to the ECM proportional to the mass of the
incoming air. This calculation allows the ECM to set the EGR ratio for varying operating conditions.

2. The AAP sensor is located in the top of the air filter housing. It provides voltage signals relative to both ambient air
pressure and temperature to the ECM. The AAP sensor produces a voltage between 0 and 5 volts proportional to the
pressure level of the air in the air filter housing. A reading of 0 volts indicates low pressure and a reading of 5 volts
indicates high pressure. The ECM uses the signal from the AAP sensor for the following functions:
l To maintain manifold boost pressure.
l To reduce exhaust smoke emissions while driving at high altitude.
l Control of the EGR system.
The sensor also supplies a voltage between 0v and 5v proportional to ambient temperature. The ECM uses this signal
for the following functions:
l Exhaust gas over temperature protection.
l Turbocharger overspeed protection.

3. The MAP/IAT sensors are combined in one unit located in the inlet manifold. It provides pressure and temperature
information about the air in the inlet manifold to the ECM. The ECM compares the voltage signal to stored values and
compensates fuel delivery as necessary. The ECM uses the signal from the MAP/IAT sensor for the following
functions:
l To calculate the delivered fuel limits.
l To calculate the air mass in the cylinder.
l To calculate the air speed density.
l To calculate air temperature.
The MAP sensor works on the piezo crystal principal. Piezo crystals are pressure sensitive and will oscillate in
accordance to changes in air pressure. The MAP sensor produces a voltage between 0 and 5 volts proportional to
the pressure level of the air in the inlet manifold. A reading of 0 volts indicates a low pressure and a reading of 5 volts
indicates a high pressure.
The IAT portion of the sensor works as a Negative Temperature Co-efficient (NTC) sensor. As air temperature rises,
the resistance in the sensor decreases. As temperature decreases the resistance in the sensor increases. The ECM
compares the voltage signal to stored values and compensates fuel delivery as necessary.

as i said, i did this on my own car when the MAF failed and now it's working better than ever (though it's manual not auto)

Well you certainly have done your homework.


I found it very difficult to believe that the sole purpose of the MAF sensor is to control the EGR system, but it appears that you are correct.


MAP and MAF, very interesting setup.

Originally Posted by sierrafery

i'm open for any friendly polemic on this believe me... your statement about the MAF is correct for other diesel and especially for petrol engines not for Td5, for temperature, altitude and weather there is the AAP sensor in the airbox, i made tests on the bench and the MAF disturbes the management only if it's faulty as open or short circuit or if it doesnt give the expected inputs, provided the EGR is bypassed, cos all the trouble which MAF can cause is when the EGR is still on and it's missmanaged by a faulty MAF(that's the gist of this, ... a lack of airflow will result in lack of boost sensed by the MAP or a depression sensed by the AAP which are responsible for fueling and boost controll, i quote the relevant parts from the book...but as i say this mod is tested live and working great ... the AAP and MAP/IAT sensors are important for Td5 management not the MAF if the EGR is bypassed


as i said, i did this on my own car when the MAF failed and now it's working better than ever (though it's manual not auto)

Have you heard of a fuel air calibration table?
It is the second or third most important tuning table in a diesel ecu.
The whole air flow axis relies on the maf reading.

Which you now don't have.

Originally Posted by Dougal

Have you heard of a fuel air calibration table?
It is the second or third most important tuning table in a diesel ecu.
The whole air flow axis relies on the maf reading.

Which you now don't have.

Rave states this information is derived from MAP sensor readings.

Originally Posted by lpower85

Rave states this information is derived from MAP sensor readings.

Carefull you will be inline for some from Dougal

Originally Posted by sierrafery

i'm open for any friendly polemic on this believe me... your statement about the MAF is correct for other diesel and especially for petrol engines not for Td5, for temperature, altitude and weather there is the AAP sensor in the airbox, i made tests on the bench and the MAF disturbes the management only if it's faulty as open or short circuit or if it doesnt give the expected inputs, provided the EGR is bypassed, cos all the trouble which MAF can cause is when the EGR is still on and it's missmanaged by a faulty MAF(that's the gist of this, ... a lack of airflow will result in lack of boost sensed by the MAP or a depression sensed by the AAP which are responsible for fueling and boost controll, i quote the relevant parts from the book...but as i say this mod is tested live and working great ... the AAP and MAP/IAT sensors are important for Td5 management not the MAF if the EGR is bypassed


as i said, i did this on my own car when the MAF failed and now it's working better than ever (though it's manual not auto)

Well put , well said Keep up the good work
Im watching with interest