Batfalcon
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What is this thing, and where is it installed?
Technical Mass Air flow Sencor
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Mass Air flow Sencor
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The Mass Air Flow Sensor or MAF for short measures the air entering the engine.
Works on a hot wire system, the faster the air passes the wire, the more voltage it takes to keep the wire at a certain temp.
It reports to the ECU which then works out the fueling/timing (based on other sensor reading like engine temp, crank speed, throttle position etc)
This is a "mass air" system.
Not all cars have them, my 1.1 Active uses a Manifold Absolute Pressure Sensor (MAP) it's a black box on the right of the throttle body and measures barometric pressure differences.
It's works slightly differently but the results are the same.
This system is called a "speed density system".
If you have a MAF, it will be in the air intake after the air filter, but before the throttle body.
MAF's are very common on diesels, but modern pertols tend to use MAP's these days.
Works on a hot wire system, the faster the air passes the wire, the more voltage it takes to keep the wire at a certain temp.
It reports to the ECU which then works out the fueling/timing (based on other sensor reading like engine temp, crank speed, throttle position etc)
This is a "mass air" system.
Not all cars have them, my 1.1 Active uses a Manifold Absolute Pressure Sensor (MAP) it's a black box on the right of the throttle body and measures barometric pressure differences.
It's works slightly differently but the results are the same.
This system is called a "speed density system".
If you have a MAF, it will be in the air intake after the air filter, but before the throttle body.
MAF's are very common on diesels, but modern pertols tend to use MAP's these days.
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I've stolen this from another site,
http://oldfuelinjection.com/?p=64
It's old but still fairly relevant.
Tells you what sensors do what when.
Start / Crank
This is the start (I know, bad joke). The EEC needs to senses several things to start an engine:
* Power to EEC and fuel pump(s)
* Slow and irregular PIP signal from the distributor (Profile Ignition Pickup)
* MAF/MAP low and irregular (Mass Air Flow/Manifold Absolute Pressure)
* TPS is closed (Throttle Position Sensor)
* HEGO shows lean (Oxygen/Lambda Sensor)
These tell the EEC that you have just checked the dash, want the engine to start, and have turned the key. Even though you've heard the fuel pumps whirr, the injectors haven't released any fuel until it senses engine rotation.
Even when the engine does turn over EEC (Electronic Engine Control or ECU or PCM) hesitates almost a full second to begin fuel and spark; this is to support oil lubrication.
ECT (Engine Coolant Temp Sensor) and ACT (Air Charg Temp Sensor) determine the amount of fuel; the colder it is the more fuel it dumps in.
The Idle Air Bypass is opened 100% to allow for operator error free starting. Spark control is taken over by the TFI (Thick Film Injection), as long as you hold the key in the start position.
What if things go bad, your ignition system could not light the engine, and it become flooded? Press the accelerator to the floor while starting, the full open TPS reading will tell the EEC to cut the injectors back to almost nothing. When you decide the fuel has been flushed out release the pedal and the EEC will fire the injectors and the engine fires up. Once the key springs into run, timing is determined by ECT and ACT, the PIP steadies out, the MAF/MAP builds, and the system bumps into the next strategy.
http://oldfuelinjection.com/?p=64
It's old but still fairly relevant.
Tells you what sensors do what when.
Start / Crank
This is the start (I know, bad joke). The EEC needs to senses several things to start an engine:
* Power to EEC and fuel pump(s)
* Slow and irregular PIP signal from the distributor (Profile Ignition Pickup)
* MAF/MAP low and irregular (Mass Air Flow/Manifold Absolute Pressure)
* TPS is closed (Throttle Position Sensor)
* HEGO shows lean (Oxygen/Lambda Sensor)
These tell the EEC that you have just checked the dash, want the engine to start, and have turned the key. Even though you've heard the fuel pumps whirr, the injectors haven't released any fuel until it senses engine rotation.
Even when the engine does turn over EEC (Electronic Engine Control or ECU or PCM) hesitates almost a full second to begin fuel and spark; this is to support oil lubrication.
ECT (Engine Coolant Temp Sensor) and ACT (Air Charg Temp Sensor) determine the amount of fuel; the colder it is the more fuel it dumps in.
The Idle Air Bypass is opened 100% to allow for operator error free starting. Spark control is taken over by the TFI (Thick Film Injection), as long as you hold the key in the start position.
What if things go bad, your ignition system could not light the engine, and it become flooded? Press the accelerator to the floor while starting, the full open TPS reading will tell the EEC to cut the injectors back to almost nothing. When you decide the fuel has been flushed out release the pedal and the EEC will fire the injectors and the engine fires up. Once the key springs into run, timing is determined by ECT and ACT, the PIP steadies out, the MAF/MAP builds, and the system bumps into the next strategy.
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Cold Start & Warm Up (open loop)
The engine has just started and we have to get adjusted. Well EEC does anyway, this strategy is kind of like you waking up with a hangover next to a stranger.
Where'd I set my pants, should I run fast, should I sneak quietly!
EEC's first reaction is to keep the throttle air bypass open 100% or else we'll be back to engine crank mode.
RPM will drop however, usually to around 1000RPM after a few seconds, then drop down to base idle as she gets warmer (about 160F/71C).
EEC looks almost completely at ECT and TPS; both indicate what will occur next. The colder the more fuel gets dumped in and the more timing added. When she gets warmer (about 170F/77C) she will lean out the mixture.
This logic will speed up the time it takes to heat up the engine and converter.
Now lets talk about what happens when last nights date wakes up (driver input). If you drive away with ECT under 185F/85C she jumps to cold drive-away strategy.
If you stay asleep and leave everything alone ECT will cross 185F/85C in about 4 minutes and we are now in a warm idle. See how confusing it all gets at this point.
BUT don't be hesitant about driving your car at any time; they wouldn't make all the strategies if you couldn't use them.
The Government wants you to drive your car as soon as you start it for economy purposes; cold cars burn more fuel so let's get them warmer quicker! Now hold on, I recommend a few seconds to ensure oil pressure, and let's hold up on the wide-open throttle assault until we have some nice warm oil for all the internals. Lets all practice common sense and a little love for our vehicles
The engine has just started and we have to get adjusted. Well EEC does anyway, this strategy is kind of like you waking up with a hangover next to a stranger.
Where'd I set my pants, should I run fast, should I sneak quietly!
EEC's first reaction is to keep the throttle air bypass open 100% or else we'll be back to engine crank mode.
RPM will drop however, usually to around 1000RPM after a few seconds, then drop down to base idle as she gets warmer (about 160F/71C).
EEC looks almost completely at ECT and TPS; both indicate what will occur next. The colder the more fuel gets dumped in and the more timing added. When she gets warmer (about 170F/77C) she will lean out the mixture.
This logic will speed up the time it takes to heat up the engine and converter.
Now lets talk about what happens when last nights date wakes up (driver input). If you drive away with ECT under 185F/85C she jumps to cold drive-away strategy.
If you stay asleep and leave everything alone ECT will cross 185F/85C in about 4 minutes and we are now in a warm idle. See how confusing it all gets at this point.
BUT don't be hesitant about driving your car at any time; they wouldn't make all the strategies if you couldn't use them.
The Government wants you to drive your car as soon as you start it for economy purposes; cold cars burn more fuel so let's get them warmer quicker! Now hold on, I recommend a few seconds to ensure oil pressure, and let's hold up on the wide-open throttle assault until we have some nice warm oil for all the internals. Lets all practice common sense and a little love for our vehicles
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Warm Idle (closed loop)
This one tends to be more about emissions. Warm idle occurs if the engine starts and ECT rises above 185F/85C, we come up to a stoplight, or place it back into neutral. The computer is programmed with a target RPM for idle, typically it's around 672RPM.
Let's break it down by system. Fuel is now closed loop with HEGO (Oxygen Sensor) switching.(trimming the fuel/air mixture).
We are now aiming for 14.7:1 A/F ratio for perfect emissions, enrichment will occur only if the ECT is above 225F/123C.
There will be no EGR (Exhaust Gas Recirculation valve) operation at these RPM's.
Timing is mildly advanced and will begin to retard after a minute.
We need hot exhaust gasses to help complete combustion and converter operation.
Air is pumped into the converter, but will dump to the atmosphere after several minutes to prevent overheating the converter.
The Throttle Air Bypass will be controlling idle, we need a nice smooth idle. Idle will increases 100-200RPM if the ECT or ACT is over 225F/123C. This RPM increase will help burn the rich mixture cooling the combustion chamber. The faster RPM speeds up the accessories, specifically the water pump and fan. Belt fans will speed up, and electric fans will need more juice from the alternator.
Warm Cruise
We have come to a point where we are happy with our speed and want to just cruise into the sunset. What sounds easy turns out to be one of the most in-depth strategies we use.
It is assumed that we citizens spend most of our time at cruise (yeah right), so we need the lowest emissions, highest economy, and moderate power at this time. The only good thing of warm cruise is that engine conditions are stable and need the least amount of safety nets.
We still have the throttle air bypass at 100% in preparation for future braking. Fuel is stabilized with the switching of the HEGO; it cycles about 10-20 times a second. To do this the fuel ratio is leaned and enriched slightly each time the HEGO switches from lean to rich.
It's like a high wire act, balancing fuel for maximum economy.
EGR is operational allowing more timing with less fear of detonation.
EGR also lowers the amount of oxygen in the mixture by about 15%; this means we don't need as much fuel.
The canister purge valve is opened to ingest fuel vapors, this allows us to cut back on fuel metering slightly more and prevents fuel vapors from escaping to the atmosphere.
Timing can be advanced to increase engine temperature and counteract EGR influence upon igniting combustion gasses.
Timing is used to control engine temps, hotter engines burn fuel more completely. And for the fuel that wasn't burned in the combustion chamber, we need extra airflow pumped into the exhaust system.
This air with the heat of the exhaust creates further break down of HC, CO, and Nox into CO2, H2O, and N2. The catalytic converter can accept all of the airflow without fear of over heating during cruise. The converter is cooled by air passing under the vehicle.
This one tends to be more about emissions. Warm idle occurs if the engine starts and ECT rises above 185F/85C, we come up to a stoplight, or place it back into neutral. The computer is programmed with a target RPM for idle, typically it's around 672RPM.
Let's break it down by system. Fuel is now closed loop with HEGO (Oxygen Sensor) switching.(trimming the fuel/air mixture).
We are now aiming for 14.7:1 A/F ratio for perfect emissions, enrichment will occur only if the ECT is above 225F/123C.
There will be no EGR (Exhaust Gas Recirculation valve) operation at these RPM's.
Timing is mildly advanced and will begin to retard after a minute.
We need hot exhaust gasses to help complete combustion and converter operation.
Air is pumped into the converter, but will dump to the atmosphere after several minutes to prevent overheating the converter.
The Throttle Air Bypass will be controlling idle, we need a nice smooth idle. Idle will increases 100-200RPM if the ECT or ACT is over 225F/123C. This RPM increase will help burn the rich mixture cooling the combustion chamber. The faster RPM speeds up the accessories, specifically the water pump and fan. Belt fans will speed up, and electric fans will need more juice from the alternator.
Warm Cruise
We have come to a point where we are happy with our speed and want to just cruise into the sunset. What sounds easy turns out to be one of the most in-depth strategies we use.
It is assumed that we citizens spend most of our time at cruise (yeah right), so we need the lowest emissions, highest economy, and moderate power at this time. The only good thing of warm cruise is that engine conditions are stable and need the least amount of safety nets.
We still have the throttle air bypass at 100% in preparation for future braking. Fuel is stabilized with the switching of the HEGO; it cycles about 10-20 times a second. To do this the fuel ratio is leaned and enriched slightly each time the HEGO switches from lean to rich.
It's like a high wire act, balancing fuel for maximum economy.
EGR is operational allowing more timing with less fear of detonation.
EGR also lowers the amount of oxygen in the mixture by about 15%; this means we don't need as much fuel.
The canister purge valve is opened to ingest fuel vapors, this allows us to cut back on fuel metering slightly more and prevents fuel vapors from escaping to the atmosphere.
Timing can be advanced to increase engine temperature and counteract EGR influence upon igniting combustion gasses.
Timing is used to control engine temps, hotter engines burn fuel more completely. And for the fuel that wasn't burned in the combustion chamber, we need extra airflow pumped into the exhaust system.
This air with the heat of the exhaust creates further break down of HC, CO, and Nox into CO2, H2O, and N2. The catalytic converter can accept all of the airflow without fear of over heating during cruise. The converter is cooled by air passing under the vehicle.
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Full-Throttle Acceleration
Seat belts on please, this is the master plan, what is the quickest route from point A to point B? Wide-Open throttle assaults of course.
The TPS signals wide open throttle to the EEC, this states that the driver doesn't care about economy or emissions and want maximum power to the wheels.
Fuel enriches to a preset level even further the colder the ACT is.
The timing jumps up to a maximum preset level around 28 degree BTDC (Before Top Dead Centre or before piston reached the top of it's stroke) and this is where the Knock plays a role.
The Knock sensor acts as a safety net. The factory does not want the EEC to bump the timing until we reach that edge.
So the Knock sensor is there to stop from blowing a ring or burning some valves.
The throttle air bypass remains at 100% giving you a larger throttle inlet and as a back up incase the throttle slams shut.
All EGR functions are stopped and the canister purge valve is closed to ensure the exact air to fuel ratios desired.
Smog pump air is dumped to atmosphere, air conditioning, electric fan, and all other high demand accessories are shut off to lessen the accessory drive load from A/C and alternator.
We also need a rev limiter and speed limiter for the safety of the vehicle; this changes from each model and engine.
Deceleration
The vehicle is moving and you lift your foot off the accelerator. EEC sense's the TPS go to closed and VSS (Vehicle Speed Sensor) signal slow.
This presents a few problems that are easily overcome.
First we have to prevent stalling; this is why the IAB (Air Idle Bypass) has been open, just in case the throttle snaps shut.
After throttle closure the Throttle Air Bypass closes slowly closes. Then it controls idle as we reach a stop and move back into warm idle strategy.
We are always thinking of emissions and burning fuel as we decelerate is a big waste. EEC turns the injectors completely off when RPM is over 1500 and the engine is over 140F/60C.
Injectors begin operating again under 1500RPM or if you hit the loud pedal.
If you don’t run a VSS you can run the risk of stalling when slowing down from over 1500RPM.
EGR is turned off but the canister purge is opened to burn off fuel vapors from the gas tank.
Timing can be advanced for two reasons; first with low airflow signals there is little chance of detonation. Secondly, advanced timing helps push back on the pistons, this helps create that engine brake effect.
Seat belts on please, this is the master plan, what is the quickest route from point A to point B? Wide-Open throttle assaults of course.
The TPS signals wide open throttle to the EEC, this states that the driver doesn't care about economy or emissions and want maximum power to the wheels.
Fuel enriches to a preset level even further the colder the ACT is.
The timing jumps up to a maximum preset level around 28 degree BTDC (Before Top Dead Centre or before piston reached the top of it's stroke) and this is where the Knock plays a role.
The Knock sensor acts as a safety net. The factory does not want the EEC to bump the timing until we reach that edge.
So the Knock sensor is there to stop from blowing a ring or burning some valves.
The throttle air bypass remains at 100% giving you a larger throttle inlet and as a back up incase the throttle slams shut.
All EGR functions are stopped and the canister purge valve is closed to ensure the exact air to fuel ratios desired.
Smog pump air is dumped to atmosphere, air conditioning, electric fan, and all other high demand accessories are shut off to lessen the accessory drive load from A/C and alternator.
We also need a rev limiter and speed limiter for the safety of the vehicle; this changes from each model and engine.
Deceleration
The vehicle is moving and you lift your foot off the accelerator. EEC sense's the TPS go to closed and VSS (Vehicle Speed Sensor) signal slow.
This presents a few problems that are easily overcome.
First we have to prevent stalling; this is why the IAB (Air Idle Bypass) has been open, just in case the throttle snaps shut.
After throttle closure the Throttle Air Bypass closes slowly closes. Then it controls idle as we reach a stop and move back into warm idle strategy.
We are always thinking of emissions and burning fuel as we decelerate is a big waste. EEC turns the injectors completely off when RPM is over 1500 and the engine is over 140F/60C.
Injectors begin operating again under 1500RPM or if you hit the loud pedal.
If you don’t run a VSS you can run the risk of stalling when slowing down from over 1500RPM.
EGR is turned off but the canister purge is opened to burn off fuel vapors from the gas tank.
Timing can be advanced for two reasons; first with low airflow signals there is little chance of detonation. Secondly, advanced timing helps push back on the pistons, this helps create that engine brake effect.
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Background Strategies:
Failure Mode
Failure mode is a stand in strategy in the EEC designed to maintain vehicle operation should one or more sensor inputs fail.
When a sensor input is perceived to be out-of-limits by the EEC, memorized data from the computers memory will be initiated.
EEC continually checks the sensors against its records of normal readings during operating conditions similar to its current state.
Hold on that sounds hard! Not really, randomly EEC looks at the past to see if the engine is somewhat where it usually is.
If for some unknown reason a sensor is off the charts, it can’t be trusted. So instead of tuning the engine to a possible faulty sensor reading and harming the engine and drive-ability; EEC replaces the sensor reading with a best guess from a past memory.
This is why unplugging the battery to fix something works against you. Unplug the battery causes EEC to memorize all the sensor data as base line and normal.
If it memorizes a bad sensor it will take it longer to call it a liar.
Manufacturers however give EEC a very broad idea of what the sensor should be reading in its permanent ROM memory, so it will catch on to failed equipment sooner.
Adaptive Strategy
Now this one is a little complex.
EEC likes to toy with the fuel ratio at random. It does this to run complex math equations.
She is calculating how much fuel is required to reach certain lean or rich states. Why you ask? Because playing this cat and mouse game with the fuel ratio allows us to fine tune the engine parameters in other strategies.
Confused yet?
EEC cuts back on the injectors for a spit second and counts how long it takes for the HEGO to report back a lean environment.
EEC leans and enriches at different amounts and get back different numbers. These numbers tell EEC if the engine needs a tune up, or if you’ve added a performance parts and allows us to actually alter the fuel amount delivered.
What do we do with those numbers EEC collected? Well there is a Table called “Adaptive Fuel Table” (makes sense huh?)
This table is used as a multiplier, it is held over the master load table. It then multiplies each number in the master table to get a better control of fuel delivery over time.
In a computer that has been just connected to the battery it is full of “1′s”, if you multiply the master table by “1″ you get the same number.
I’m not good at math and I understand it, 14.7:1 X 1 = 14.7:1, simple!
After many days of driving on the highway it begins to fill with multipliers like “1.2′s” and “0.9′s”, which will alter the master table. Don’t believe me? 14.7:1 X 1.2 = 17.6:1, and 14.7:1 X 0.9 = 13.3:1, and we just fine tuned our fuel curve without doing anything special.
Isn’t that cool?
Well not always, this entire technology depends on the Oxygen Sensors being fresh, clean, new, and in good condition. And it can’t be responsible for displacement changes, cam changes, or other big performance add-on’s. This technology is only meant to keep EEC on the same level as an ageing engine with diminished performance. It is not meant to be relied upon for performance engine tuning!
Well that kept me busy for a while!
Failure Mode
Failure mode is a stand in strategy in the EEC designed to maintain vehicle operation should one or more sensor inputs fail.
When a sensor input is perceived to be out-of-limits by the EEC, memorized data from the computers memory will be initiated.
EEC continually checks the sensors against its records of normal readings during operating conditions similar to its current state.
Hold on that sounds hard! Not really, randomly EEC looks at the past to see if the engine is somewhat where it usually is.
If for some unknown reason a sensor is off the charts, it can’t be trusted. So instead of tuning the engine to a possible faulty sensor reading and harming the engine and drive-ability; EEC replaces the sensor reading with a best guess from a past memory.
This is why unplugging the battery to fix something works against you. Unplug the battery causes EEC to memorize all the sensor data as base line and normal.
If it memorizes a bad sensor it will take it longer to call it a liar.
Manufacturers however give EEC a very broad idea of what the sensor should be reading in its permanent ROM memory, so it will catch on to failed equipment sooner.
Adaptive Strategy
Now this one is a little complex.
EEC likes to toy with the fuel ratio at random. It does this to run complex math equations.
She is calculating how much fuel is required to reach certain lean or rich states. Why you ask? Because playing this cat and mouse game with the fuel ratio allows us to fine tune the engine parameters in other strategies.
Confused yet?
EEC cuts back on the injectors for a spit second and counts how long it takes for the HEGO to report back a lean environment.
EEC leans and enriches at different amounts and get back different numbers. These numbers tell EEC if the engine needs a tune up, or if you’ve added a performance parts and allows us to actually alter the fuel amount delivered.
What do we do with those numbers EEC collected? Well there is a Table called “Adaptive Fuel Table” (makes sense huh?)
This table is used as a multiplier, it is held over the master load table. It then multiplies each number in the master table to get a better control of fuel delivery over time.
In a computer that has been just connected to the battery it is full of “1′s”, if you multiply the master table by “1″ you get the same number.
I’m not good at math and I understand it, 14.7:1 X 1 = 14.7:1, simple!
After many days of driving on the highway it begins to fill with multipliers like “1.2′s” and “0.9′s”, which will alter the master table. Don’t believe me? 14.7:1 X 1.2 = 17.6:1, and 14.7:1 X 0.9 = 13.3:1, and we just fine tuned our fuel curve without doing anything special.
Isn’t that cool?
Well not always, this entire technology depends on the Oxygen Sensors being fresh, clean, new, and in good condition. And it can’t be responsible for displacement changes, cam changes, or other big performance add-on’s. This technology is only meant to keep EEC on the same level as an ageing engine with diminished performance. It is not meant to be relied upon for performance engine tuning!
Well that kept me busy for a while!
OP
OP
Batfalcon
New member
Thanks A LOT Goudrons!!!!
I haven't read an article from top to bottom with such an appetite.
I haven't read an article from top to bottom with such an appetite.
OP
OP
Batfalcon
New member
Can someone tell me guys, where exactly is this MAF/ MAP sensor on a 1.2 petrol engine?
Plus, do you ever clean it somehow, or not?
Plus, do you ever clean it somehow, or not?
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It's a MAP sensor you have on a petrol Panda.
Looks like this
http://www.eurocarparts.com/ecp/c/F...84139ed24a06b7448e8ecf90ad76ea9bd29810&000515
It's bolted into the right side of the throttle body, under the air filter box.
It won't need cleaning like a MAF.
MAFs, as descrided run a hot wire which can attract dirty, a MAP is a bladder that detects pressure change.
Looks like this
http://www.eurocarparts.com/ecp/c/F...84139ed24a06b7448e8ecf90ad76ea9bd29810&000515
It's bolted into the right side of the throttle body, under the air filter box.
It won't need cleaning like a MAF.
MAFs, as descrided run a hot wire which can attract dirty, a MAP is a bladder that detects pressure change.
OP
OP
Batfalcon
New member
Thanks for the info (again) 
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