Intake air temperature

[wammers]

There are 5 wires to the MAF, power, ground, flow sensor and temperature sensor.

Function as per RAVE below.

[FONT=Arial, sans-serif]Mass Air Flow Sensor (X105)[/FONT]
[FONT=Arial, sans-serif]The Mass Air Flow Sensor (X105) is a hot film[/FONT]
[FONT=Arial, sans-serif]sensor which has a heated surface maintained by an[/FONT]
[FONT=Arial, sans-serif]electrical current at a constant temperature. With[/FONT]
[FONT=Arial, sans-serif]cool air flowing past the sensor, the volume of air[/FONT]
[FONT=Arial, sans-serif]drawn into the intake manifold is measured by the[/FONT]
[FONT=Arial, sans-serif]electrical current required to keep the temperature of[/FONT]
[FONT=Arial, sans-serif]the hot film sensor constant. This data is used to[/FONT]
[FONT=Arial, sans-serif]calculate the injected fuel volume and the rate of[/FONT]
[FONT=Arial, sans-serif]Exhaust Gas Recirculation (EGR).[/FONT]
[FONT=Arial, sans-serif]The intake air temperature is measured by a[/FONT]
[FONT=Arial, sans-serif]thermistor with a negative temperature co–efficient[/FONT]
[FONT=Arial, sans-serif]and measures the actual temperature of the turbo[/FONT]
[FONT=Arial, sans-serif]booster air entering the engine. The ECM (Z132)[/FONT]
[FONT=Arial, sans-serif]uses this information, in conjunction with the[/FONT]
[FONT=Arial, sans-serif]manifold absolute pressure sensor, to determine the[/FONT]
[FONT=Arial, sans-serif]volume of air being drawn into the engine.[/FONT]

Where is the IAT sensor that measures the actual temp of the air going into the manifold after the turbo on the EGR engine? As is done on the non EGR engine. Statement marked in red. You can't do that at the MAF. That is why it is a low preset to force the EGR to work under all conditions. The temp sensor in the MAF is there so the ECU knows the air temp at the MAF, so it can workout the correct air flow through it. It is NOT used for fuel calculations. Neither the MAF air flow nor the MAF temp is readable on any diagnostics as far as i am aware. If they were needed for fuelling they would be. The MAF is there to fine tune the EGR as required by EC level 2 regulations (EGR feedback control) as stated in BMW service bulletins dated 11/04/96.

 

[Datatek]

Where is the IAT sensor that measures the actual temp of the air going into the manifold after the turbo on the EGR engine? As is done on the non EGR engine. Statement marked in red. You can't do that at the MAF. That is why it is a low preset to force the EGR to work under all conditions. The temp sensor in the MAF is there so the ECU knows the air temp at the MAF, so it can workout the correct air flow through it. It is NOT used for fuel calculations. Neither the MAF air flow nor the MAF temp is readable on any diagnostics as far as i am aware. If they were needed for fuelling they would be. The MAF is there to fine tune the EGR as required by EC level 2 regulations (EGR feedback control) as stated in BMW service bulletins dated 11/04/96.

Of course you can measure the intake air temperature at the MAF and of course it's not the same as the manifold temperature. Lots of vehicles measure intake air temperature at the MAF including all petrol engines including turbo that I've seen. Airflow through the MAF is calculated by the cooling effect of the airflow on the hot film detector, the greater the flow, the greater the cooling effect, however colder air would give a false flow reading if there was not a temperature reference to compensate.
On a turbo diesel, the opening of the EGR can only be allowed when the exhaust pressure exceeds inlet manifold pressure, I'd be interested to know how that can be derived from airflow alone.

 

[wammers]

Of course you can measure the intake air temperature at the MAF and of course it's not the same as the manifold temperature. Lots of vehicles measure intake air temperature at the MAF including all petrol engines including turbo that I've seen. Airflow through the MAF is calculated by the cooling effect of the airflow on the hot film detector, the greater the flow, the greater the cooling effect, however colder air would give a false flow reading if there was not a temperature reference to compensate.
On a turbo diesel, the opening of the EGR can only be allowed when the exhaust pressure exceeds inlet manifold pressure, I'd be interested to know how that can be derived from airflow alone.

Petrol engines work on an entirely different principal to diesels as you should well know. They are throttled by air not by fuel as in the diesel. Petrol engines have fuel monitored subject to air flow to maintain the correct mixture ratio of around 14 to 1. Diesels do not, for any given RPM, manifold pressure, there is always the same amount of air in the cylinder of a diesel engine. Fuel is injected to maintain the requested RPM or power demand. Whether that be at idle RPM or max RPM or any transition between the two. The fuel to air ratio can be well over a hundred to one at idle. EGR operation only takes place at certain times it is not a continuous function. It does not function at idle, on acceleration nor at high engine loads. If there is an EGR malfunction on acceleration or at high engine loads a serious loss of power would result. The pressure in the exhaust system will always be higher than the manifold pressure. The EGR system is for reducing the production of NOx nothing else. To do this it needs to control dense air supply to starve the combustion process of excessive Oxygen that produces an hot burn. Fuel injected for any desired RPM, power level, manifold pressure remains the same. The EGR introduces exhaust gas into the manifold to reduce the amount of Oxygenated air in the charge. It basically replaces the Oxygenated air with exhaust gas, that the engine does not need, to run at the requested throttle setting. Subject to certain parameters fore mentioned.

 

[Datatek]

Petrol engines work on an entirely different principal to diesels as you should well know. They are throttled by air not by fuel as in the diesel. Petrol engines have fuel monitored subject to air flow to maintain the correct mixture ratio of around 14 to 1. Diesels do not, for any given RPM, manifold pressure, there is always the same amount of air in the cylinder of a diesel engine. Fuel is injected to maintain the requested RPM or power demand. Whether that be at idle RPM or max RPM or any transition between the two. The fuel to air ratio can be well over a hundred to one at idle. EGR operation only takes place at certain times it is not a continuous function. It does not function at idle, on acceleration nor at high engine loads. If there is an EGR malfunction on acceleration or at high engine loads a serious loss of power would result. The pressure in the exhaust system will always be higher than the manifold pressure. The EGR system is for reducing the production of NOx nothing else. To do this it needs to control dense air supply to starve the combustion process of excessive Oxygen that produces an hot burn. Fuel injected for any desired RPM, power level, manifold pressure remains the same. The EGR introduces exhaust gas into the manifold to reduce the amount of Oxygenated air in the charge. It basically replaces the Oxygenated air with exhaust gas, that the engine does not need, to run at the requested throttle setting. Subject to certain parameters fore mentioned.

As I said, the EGR cannot operate when the inlet manifold pressure exceeds the exhaust pressure. EGR operation on a turbo diesel is not straightforward unlike a NA diesel.

 

[wammers]

As I said, the EGR cannot operate when the inlet manifold pressure exceeds the exhaust pressure. EGR operation on a turbo diesel is not straightforward unlike a NA diesel.

The exhaust pressure will always exceed manifold pressure at the times when EGR is used. That is why with an EGR fail (stuck open or open at the wrong time) there is a dramatic loss of power. Usually with black smoke, as the air present is insufficient for the fuel being injected to satisfy the throttle power request.

 

[Datatek]

The exhaust pressure will always exceed manifold pressure at the times when EGR is used. That is why with an EGR fail (stuck open or open at the wrong time) there is a dramatic loss of power. Usually with black smoke, as the air present is insufficient for the fuel being injected to satisfy the throttle power request.

But the system has to know when that condition will be satisfied in order to operate the EGR.

 

[wammers]

But the system has to know when that condition will be satisfied in order to operate the EGR.

There will always be more pressure in the exhaust system than in the manifold, when the EGR operates it only works in low throttle demand conditions.

 

[Datatek]

There will always be more pressure in the exhaust system than in the manifold, when the EGR operates it only works in low throttle demand conditions.

And just how do you think the EDC knows that?

 

[wammers]

And just how do you think the EDC knows that?

Road speed, manifold pressure, throttle demand. Nothing to do with airflow through the MAF if that's where you are heading.

 

[Datatek]

Road speed, manifold pressure, throttle demand. Nothing to do with airflow through the MAF if that's where you are heading.

Ah, so now the MAF is not even used for airflow for the EGR.

 

[wammers]

Ah, so now the MAF is not even used for airflow for the EGR.

Keith give it up mate, i have explained in great detail how the EGR works, what the MAF is for and how it monitors air for the EGR. If you can't understand it that is not my problem.

 

[Datatek]

Road speed, manifold pressure, throttle demand. Nothing to do with airflow through the MAF if that's where you are heading.

Keith give it up mate, i have explained in great detail how the EGR works, what the MAF is for and how it monitors air for the EGR. If you can't understand it that is not my problem.

You have previously stated that the MAF is nothing to do with fuelling (despite RAVE stating the contrary) and now you say airflow through the MAF is also nothing to do with the EGR. So according to you it serves no purpose at all.

 

[wammers]

You have previously stated that the MAF is nothing to do with fuelling (despite RAVE stating the contrary) and now you say airflow through the MAF is also nothing to do with the EGR. So according to you it serves no purpose at all.

THE MAF HAS NOTHING TO DO WITH FUELLING IT FINE CONTROLS THE EGR. I DID NOT SAY THE MAF HAS NOTHING TO DO WITH EGR. The ECU decides when EGR is activated from other sensors NOT from the air flow through the MAF. The airflow through the MAF is used by the ECU to determine the amount of EGR being applied. That is all. Now either understand how it works or drop it for christ sake.

 

[Datatek]

THE MAF HAS NOTHING TO DO WITH FUELLING IT FINE CONTROLS THE EGR. I DID NOT SAY THE MAF HAS NOTHING TO DO WITH EGR. The ECU decides when EGR is activated from other sensors NOT from the air flow through the MAF. The airflow through the MAF is used by the ECU to determine the amount of EGR being applied. That is all. Now either understand how it works or drop it for christ sake.

But if as you said it has nothing to do with air flow and nothing to do with fueling what's it there for? I'm only quoting what you have said back at you. Personally I agree with the RAVE description of what the MAF does. You keep shouting the same thing but it appears just to be an opinion with nothing of substance to support it.

 

[wammers]

But if as you said it has nothing to do with air flow and nothing to do with fueling what's it there for? I'm only quoting what you have said back at you. Personally I agree with the RAVE description of what the MAF does. You keep shouting the same thing but it appears just to be an opinion with nothing of substance to support it.

Then you have little concept of how a diesel engine works. The MAF measures air flow so the ECU knows how much exhaust gas is being ingested at any particular time to reduce Oxygen content, so as to reduce NOx production. Without EGR the Oxygenated air content (subject to air temp) of the charge at any particular RPM boost pressure is constant. Fuel required to maintain any particular RPM within smoke generation parameters mapped into the ECU, for any given power level/throttle request is constant. Subject to minor adjustments for fuel temperature and on the non EGR engine inlet air temperature. On the EGR engine inlet air temperature is a low preset to ensure that the ECU thinks the charge is high density cold air. This ensures EGR operation at all ambient air temperatures. EGR introduces exhaust gas into the air charge to reduce the Oxygen content so reducing the burn temperature, it leaves only the Oxygenated air required to burn the metered fuel injected, to maintain any particular RPM or power request. Too little exhaust gas NOx is produced too much exhaust gas power levels fall and RPM drops.

 

[N5Fav]

And I thought I was asking a straight forward question, I hadn't intended anybody getting hot under the collar.

So if IAT has no purposeful reading, why bother to enable diagnostics tools to see it? wouldn't it be better if a set value was pre-programmed into the ECU and left at that.

I'm sorry wammers, but I can't see how a setting an artificially low IAT reading would be used to affect EGR activity, surely LR / BMW would have just written the software with different parameter requirements?

I will continue to look into this though so don't shoot me down in flames. :flame::fighting:

PS, thanks for all the input to far.

 

[wammers]

And I thought I was asking a straight forward question, I hadn't intended anybody getting hot under the collar.

So if IAT has no purposeful reading, why bother to enable diagnostics tools to see it? wouldn't it be better if a set value was pre-programmed into the ECU and left at that.

I'm sorry wammers, but I can't see how a setting an artificially low IAT reading would be used to affect EGR activity, surely LR / BMW would have just written the software with different parameter requirements?

I will continue to look into this though so don't shoot me down in flames. :flame::fighting:

PS, thanks for all the input to far.

I can understand why they would do it. It does have a purposeful reading. Cold air at standard atmospheric pressure is denser than hot air, think about it. The reason has been explained, you can either believe it or not to be honest, i don't really care.