How the MAF works
Thread Starter
100% chingon
Joined: Oct 2005
Posts: 1,003
How the MAF works
I removed the MAF for the first time today and saw for the first time exactly what it is. The MAF is surprisingly simple. It should never go wrong except by greasy human fingers getting in there..
The MAF sensor is nothing more or less than a simple electrical component called a thermistor, in this case it is a very small bead thermistor. Small, because it needs to have a small thermal mass so as to respond quickly to changes in air flow.
A thermistor is just a thermally-sensitive resistor. The ECU passes a small current through the thermistor and it heats up, quickly reaching a 'steady state'. This is just before you start the car. As soon as you start the engine, the flow of air past the thermistor cools it down, and as it cools, its resistance changes. In other words, the resistance of the thermistor is proportional to the flow of air, more air = cooler = higher resistance.
Interestingly, it should be possible to build a circuit to piggy-back on the MAF and allow you to 'fine tune' the MAF output to tell the motor it's really getting more or less air than it is, thus adjusting the mixture! Of course if you went too far outside the parameters the ECU would detect a problem and throw a code and go back to using open-loop. Not that I am suggesting such a thing, I just mention it as a possibility, being an engineer.
Since the MAF is merely a bead thermistor, you might like to know what a bead thermistor typically costs. Anything from about 25 cents to around a dollar or so.
Therefore it should be possible to repair a dead MAF easily enough for almost no money, just using a little skill and a temperature-regulated soldering iron like the Weller TP60.
There's only one problem: knowing the type number of the bead thermistor.
Is there anyone with a spy at Nissan, please?
I bet it's a standard type from one of the electronic parts companies.
If we can't find the number it should be possible to match it by measurement of the resistance at various temperatures but that's not something I want to spend time on right now
The MAF sensor is nothing more or less than a simple electrical component called a thermistor, in this case it is a very small bead thermistor. Small, because it needs to have a small thermal mass so as to respond quickly to changes in air flow.
A thermistor is just a thermally-sensitive resistor. The ECU passes a small current through the thermistor and it heats up, quickly reaching a 'steady state'. This is just before you start the car. As soon as you start the engine, the flow of air past the thermistor cools it down, and as it cools, its resistance changes. In other words, the resistance of the thermistor is proportional to the flow of air, more air = cooler = higher resistance.
Interestingly, it should be possible to build a circuit to piggy-back on the MAF and allow you to 'fine tune' the MAF output to tell the motor it's really getting more or less air than it is, thus adjusting the mixture! Of course if you went too far outside the parameters the ECU would detect a problem and throw a code and go back to using open-loop. Not that I am suggesting such a thing, I just mention it as a possibility, being an engineer.
Since the MAF is merely a bead thermistor, you might like to know what a bead thermistor typically costs. Anything from about 25 cents to around a dollar or so.
Therefore it should be possible to repair a dead MAF easily enough for almost no money, just using a little skill and a temperature-regulated soldering iron like the Weller TP60.
There's only one problem: knowing the type number of the bead thermistor.
Is there anyone with a spy at Nissan, please?
I bet it's a standard type from one of the electronic parts companies.
If we can't find the number it should be possible to match it by measurement of the resistance at various temperatures but that's not something I want to spend time on right now
Originally Posted by clive
It should never go wrong except by greasy human fingers getting in there.
Originally Posted by clive
I removed the MAF for the first time today and saw for the first time exactly what it is. The MAF is surprisingly simple. It should never go wrong except by greasy human fingers getting in there..
The MAF sensor is nothing more or less than a simple electrical component called a thermistor, in this case it is a very small bead thermistor. Small, because it needs to have a small thermal mass so as to respond quickly to changes in air flow.
A thermistor is just a thermally-sensitive resistor. The ECU passes a small current through the thermistor and it heats up, quickly reaching a 'steady state'. This is just before you start the car. As soon as you start the engine, the flow of air past the thermistor cools it down, and as it cools, its resistance changes. In other words, the resistance of the thermistor is proportional to the flow of air, more air = cooler = higher resistance.
Interestingly, it should be possible to build a circuit to piggy-back on the MAF and allow you to 'fine tune' the MAF output to tell the motor it's really getting more or less air than it is, thus adjusting the mixture! Of course if you went too far outside the parameters the ECU would detect a problem and throw a code and go back to using open-loop. Not that I am suggesting such a thing, I just mention it as a possibility, being an engineer.
Since the MAF is merely a bead thermistor, you might like to know what a bead thermistor typically costs. Anything from about 25 cents to around a dollar or so.
Therefore it should be possible to repair a dead MAF easily enough for almost no money, just using a little skill and a temperature-regulated soldering iron like the Weller TP60.
There's only one problem: knowing the type number of the bead thermistor.
Is there anyone with a spy at Nissan, please?
I bet it's a standard type from one of the electronic parts companies.
If we can't find the number it should be possible to match it by measurement of the resistance at various temperatures but that's not something I want to spend time on right now
The MAF sensor is nothing more or less than a simple electrical component called a thermistor, in this case it is a very small bead thermistor. Small, because it needs to have a small thermal mass so as to respond quickly to changes in air flow.
A thermistor is just a thermally-sensitive resistor. The ECU passes a small current through the thermistor and it heats up, quickly reaching a 'steady state'. This is just before you start the car. As soon as you start the engine, the flow of air past the thermistor cools it down, and as it cools, its resistance changes. In other words, the resistance of the thermistor is proportional to the flow of air, more air = cooler = higher resistance.
Interestingly, it should be possible to build a circuit to piggy-back on the MAF and allow you to 'fine tune' the MAF output to tell the motor it's really getting more or less air than it is, thus adjusting the mixture! Of course if you went too far outside the parameters the ECU would detect a problem and throw a code and go back to using open-loop. Not that I am suggesting such a thing, I just mention it as a possibility, being an engineer.
Since the MAF is merely a bead thermistor, you might like to know what a bead thermistor typically costs. Anything from about 25 cents to around a dollar or so.
Therefore it should be possible to repair a dead MAF easily enough for almost no money, just using a little skill and a temperature-regulated soldering iron like the Weller TP60.
There's only one problem: knowing the type number of the bead thermistor.
Is there anyone with a spy at Nissan, please?
I bet it's a standard type from one of the electronic parts companies.
If we can't find the number it should be possible to match it by measurement of the resistance at various temperatures but that's not something I want to spend time on right now
Originally Posted by clive
The MAF sensor is nothing more or less than a simple electrical component called a thermistor, in this case it is a very small bead thermistor ... being an engineer.
The thermister in the MAF is used for temperature compensation. It is the thin platinum film-type probe that is used for flow sensing.
Originally Posted by I30tMikeD
An SAFC does just about that. Intercepts the MAF signal to the ECU and changes the voltage so the ECU thinks there is either more or less air entering the motor, thus changing the injector pulse width.
That's what I was going to chime in with.-Nick
Member
Joined: Aug 2003
Posts: 69
I think you'll just set a code by changing the MAF output. The oxygen sensor is actually the feedback device and if it measures rich it will lean out the mixture regardless. The MAF signal is just used to map the ECU and put it in the right area.
Droz
Droz
Originally Posted by RDroz
I think you'll just set a code by changing the MAF output. The oxygen sensor is actually the feedback device and if it measures rich it will lean out the mixture regardless. The MAF signal is just used to map the ECU and put it in the right area.
Droz
Droz
Originally Posted by RDroz
Ah. Off-road modifications. 
I was thinking he was looking to boost performance with a stock street Maxima where you still use the original fuel design.
Droz
I was thinking he was looking to boost performance with a stock street Maxima where you still use the original fuel design.
Droz
Cars with AFCs are totally streetable and will pass emissions testing with no problems
Member
Joined: Aug 2003
Posts: 69
OK. I would have thought that modifying (or being able to modify) the AFR would automatically void warrenty and make the car "emissions illegal".
Is there much of a horsepower increase with one of these on a stock engine? Or is it mostly for heavily modified motors?
Droz
Is there much of a horsepower increase with one of these on a stock engine? Or is it mostly for heavily modified motors?
Droz
Originally Posted by RDroz
Is there much of a horsepower increase with one of these on a stock engine? Or is it mostly for heavily modified motors?
Manipulating MAF voltage has other indirect effects.
http://www.forums.maxima.org/showthread.php?t=434821
Thread Starter
100% chingon
Joined: Oct 2005
Posts: 1,003
Originally Posted by eng92
If you are a mechanical engineer, you should be very familiar with the hot-wire and hot-film anemometry methods for flow measurement and the fact that they do not use a thermistor for a flow sensor.
The thermister in the MAF is used for temperature compensation. It is the thin platinum film-type probe that is used for flow sensing.
The thermister in the MAF is used for temperature compensation. It is the thin platinum film-type probe that is used for flow sensing.
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