Why understanding Sensors is important

[Bike31]

I thought the purpose of the MAP was to estimate the air density (mass) of the incoming air. Mass = air pressure, temperature, and humidity. The last component being unknown in this case. Depending upon mass and rpm (estimate of intake air volume) the ECM determines fuel flow (Edit: and timing of ignition). My 0.02.

[joe_lyons]

Would this be more appropriate?

[joe_lyons]

Or is that other table just the error for temperature output?

[guydoc77]

I'm sure I'll get corrected however isn't the big picture that the MAP sensor reads whatever it reads to allow a calculation on the momentary air flow into the motor? And that calculation is used in an algorithm to determine the injector PW.

So the question is what does the MAP measure.
Flow or pressure or whatever. Given the units it is pressure and given the Delphi attachment temp as well, and it's output is in voltage.

Here's my question. In a NA motor the pressure in the manifold can't ever really be above ambient pressure correct? As the piston moves down with an open valve the only pressure available to fill the void being created is atmospheric pressure. We speak in terms of vacuum and that works for me intellectually but is there really vacuum or is the air just rushing in due to Delta P between the outside of the engine (current barometric pressure) and the momentary lower pressure in the cylinder? In other words, if I'm some little person from Gulliver's Travels, and I'm standing in the intake manifold where the MAP sensor is mounted, aren't I just going to feel wind blowing on me? Wind after all, is just air moving along pressure gradients. Stronger the wind, the higher the gradient(s). In a VTwin motor that wind is dependent on throttle position, RPM, cam specs, valve open or closed, heads, and position of piston(s) in cylinder.

Let the grilling begin.

[tjwallib]

Using 1.5 for the temperature error multiplier for both plus and minus variation,,,,,,,the sensor in a chamber with a 20kpa pressure could give us a reading anywhere from 23.6kpa to 16.4kpa,,,,,at least that's my "take" on it.

[whittlebeast]

This will all turn out to be very academic once we get to the fueling equation.

[guydoc77]

This will all turn out to be very academic once we get to the fueling equation.

Agreed...

[fbn ent]

I'm sure I'll get corrected however isn't the big picture that the MAP sensor reads whatever it reads to allow a calculation on the momentary air flow into the motor? And that calculation is used in an algorithm to determine the injector PW.

So the question is what does the MAP measure.
Flow or pressure or whatever. Given the units it is pressure and given the Delphi attachment temp as well, and it's output is in voltage.

Here's my question. In a NA motor the pressure in the manifold can't ever really be above ambient pressure correct? As the piston moves down with an open valve the only pressure available to fill the void being created is atmospheric pressure. We speak in terms of vacuum and that works for me intellectually but is there really vacuum or is the air just rushing in due to Delta P between the outside of the engine (current barometric pressure) and the momentary lower pressure in the cylinder? In other words, if I'm some little person from Gulliver's Travels, and I'm standing in the intake manifold where the MAP sensor is mounted, aren't I just going to feel wind blowing on me? Wind after all, is just air moving along pressure gradients. Stronger the wind, the higher the gradient(s). In a VTwin motor that wind is dependent on throttle position, RPM, cam specs, valve open or closed, heads, and position of piston(s) in cylinder.

Let the grilling begin.

I know where you are coming from but in the '57 Dodge pickup the only way to really get the vacuum wipers to work was to let off the throttle....

[FLTRI]

This will all turn out to be very academic...

I think that is the purpose.
Bob

[joe_lyons]

I'm sure I'll get corrected however isn't the big picture that the MAP sensor reads whatever it reads to allow a calculation on the momentary air flow into the motor? And that calculation is used in an algorithm to determine the injector PW.

So the question is what does the MAP measure.
Flow or pressure or whatever. Given the units it is pressure and given the Delphi attachment temp as well, and it's output is in voltage.

Here's my question. In a NA motor the pressure in the manifold can't ever really be above ambient pressure correct? As the piston moves down with an open valve the only pressure available to fill the void being created is atmospheric pressure. We speak in terms of vacuum and that works for me intellectually but is there really vacuum or is the air just rushing in due to Delta P between the outside of the engine (current barometric pressure) and the momentary lower pressure in the cylinder? In other words, if I'm some little person from Gulliver's Travels, and I'm standing in the intake manifold where the MAP sensor is mounted, aren't I just going to feel wind blowing on me? Wind after all, is just air moving along pressure gradients. Stronger the wind, the higher the gradient(s). In a VTwin motor that wind is dependent on throttle position, RPM, cam specs, valve open or closed, heads, and position of piston(s) in cylinder.

Let the grilling begin.

I know where you are coming from but in the '57 Dodge pickup the only way to really get the vacuum wipers to work was to let off the throttle....

Yes because you are restricting the flow of air with the throttle blade causing a vac and that's how the wipers worked.  Full throttle slow to no wiper movement, decell would have great wiper movement.  Today's lesson is just about the sensors.

Are we hitting the point Cole?

[Steve Cole]

Great, Now you are looking and reading, That's a good thing as you can see for yourself the Sensor is incapable of giving you an exact reading. All we know for sure is that it is within a range of values based on the tables listed. As long as it gives a reading within that range the sensor itself is doing it's job. That doesn't mean each and everytime you are going to get the same reading, it just means it will be within the allowable range of values. No matter what anything else does, with the sensor it can never be better than what the sensor itself is capable of doing. Now it can be worse (and many times is) if you do not apply and use the provided corrections. In this case it is temperature correction and yes it increases the range of error.

So why is this very important?  The main reason is you have to allow for these errors and KNOW they are there to start with. So if, the amount of error is unacceptable, from this sensor you must move to a better piece if it exist. In many cases there will be some better and some worse. When this is the case you have a choice to balance cost again quality but in some cases there just is no choice.

[fbn ent]

So, please explain Steve. What is this "multiplier" for temperature?

[joe_lyons]

I'm sure I'll get corrected however isn't the big picture that the MAP sensor reads whatever it reads to allow a calculation on the momentary air flow into the motor? And that calculation is used in an algorithm to determine the injector PW.

So the question is what does the MAP measure.
Flow or pressure or whatever. Given the units it is pressure and given the Delphi attachment temp as well, and it's output is in voltage.

Here's my question. In a NA motor the pressure in the manifold can't ever really be above ambient pressure correct? As the piston moves down with an open valve the only pressure available to fill the void being created is atmospheric pressure. We speak in terms of vacuum and that works for me intellectually but is there really vacuum or is the air just rushing in due to Delta P between the outside of the engine (current barometric pressure) and the momentary lower pressure in the cylinder? In other words, if I'm some little person from Gulliver's Travels, and I'm standing in the intake manifold where the MAP sensor is mounted, aren't I just going to feel wind blowing on me? Wind after all, is just air moving along pressure gradients. Stronger the wind, the higher the gradient(s). In a VTwin motor that wind is dependent on throttle position, RPM, cam specs, valve open or closed, heads, and position of piston(s) in cylinder.

Let the grilling begin.

The MAP sensor just measures absolute pressure where as a TMAP sensor also has a thermistor built in for convenience and space saving.  Yes, in theory you can not exceed the current barro pressure. 

[tjwallib]

My guess is the "lesson" is that we're dealing with a number of possible variations from "actual" events/conditions with the current sensors/systems on the HD fuel injection system. There maybe alternatives in the market place, but are they cost effective and applicable on a car or motorcycle for everyday use.

Knowing that the information available provided to the ECM's internal programs could be so wildly variable, we need to come to terms with it.

NB O2 sensors have "tolerances" in their outputs, WB O2 sensors have "tolerances" in their outputs,  MAP sensors have "tolerances" in their outputs, the combustion process in an engine is not a "stable" event from revolution to revolution.  Let the ECM and internal programming do it's thing and work with the "averages" and ranges of info that it receives.

I am by no means an expert, as I know many of the good folks on this forum could "bury me" with their knowledge and experience in tuning bikes well. But I sometimes think that folks are trying to pick "fly sh*t" out of pepper when it comes to the process,,,,,,,when in many ways it doesn't really matter because the info/data we're receiving from the sensors is so potentially variable.

Not many of the folks on this forum or out there on the road are racing their bikes where the last "tid bit" of power is actually useable or will make a difference. We just want a bike that will perform well and reliably,,,,,,,hopefully better than our buddies that we ride with.

I know I'm a "newbie" on the forum, my intention isn't to piss anyone off. I enjoy the reading and learning.

[joe_lyons]

My guess is the "lesson" is that we're dealing with a number of possible variations from "actual" events/conditions with the current sensors/systems on the HD fuel injection system. There maybe alternatives in the market place, but are they cost effective and applicable on a car or motorcycle for everyday use.

Knowing that the information available provided to the ECM's internal programs could be so wildly variable, we need to come to terms with it.

NB O2 sensors have "tolerances" in their outputs, WB O2 sensors have "tolerances" in their outputs,  MAP sensors have "tolerances" in their outputs, the combustion process in an engine is not a "stable" event from revolution to revolution.  Let the ECM and internal programming do it's thing and work with the "averages" and ranges of info that it receives.

I am by no means an expert, as I know many of the good folks on this forum could "bury me" with their knowledge and experience in tuning bikes well. But I sometimes think that folks are trying to pick "fly sh*t" out of pepper when it comes to the process,,,,,,,when in many ways it doesn't really matter because the info/data we're receiving from the sensors is so potentially variable.

Not many of the folks on this forum or out there on the road are racing their bikes where the last "tid bit" of power is actually useable or will make a difference. We just want a bike that will perform well and reliably,,,,,,,hopefully better than our buddies that we ride with.

I know I'm a "newbie" on the forum, my intention isn't to piss anyone off. I enjoy the reading and learning.

There is a lot of "picking fly $hit out of pepper".  And the end all is making the motor happy.  Sometimes the ECM cannot comprehend everything or control it.  Sometimes we have to finagle things to make to motor happy.

[Coyote]

Guys, subsequent posts should be kept on topic. If you don't like the material or how it's presented or the presenter, then do not participate in this topic. Thanks.

[UltraNutZ]

Joe, couple of questions for you sir.

   
• what is the specific range the ECM is capable of compensating for on it's own say for the VE tables, and AFR? 
• Does that compensating range vary by model year or specific part # of ECM itself? 
• Is it a % number or is it a set number depending on the table?

Thanks
NutZ

[UltraNutZ]

disregard my question Joe.  the more I think about it, the ECM in my mind is nothing but a 12v powered calculator that calculates what the sensors are feeding it.

[FLTRI]

disregard my question Joe.  the more I think about it, the ECM in my mind is nothing but a 12v powered calculator that calculates what the sensors are feeding it.

[whittlebeast]

This EFI stuff gets really easy once you understand the basic sensors and the basic math that the "calculator " is using.  In the Harley world, the map sensor is by far, the most complex.

This thread keeps skirting around the interesting part of the MAP sensor and how the ECU is forced to deal with what the sensor is "seeing" in the intake.

[fbn ent]

I have a feeling we will get there.

[rageglide]

Sitting in my seat, pencil in hand, hater filter turned on.  Ready to learn as much that fits in my head.       

[Bike31]

If it somehow doesn't work perfectly would we know it?

[whittlebeast]

If it somehow doesn't work perfectly would we know it?

Errors of a couple of pct, it is doubtful you would ever notice.  A dead sensor is very noticable and very easy to diagnose  with the tools to look.  Electrical noise in the sensor wiring fooling the ECU, can be more challenging to find.

[rbabos]

This EFI stuff gets really easy once you understand the basic sensors and the basic math that the "calculator " is using.  In the Harley world, the map sensor is by far, the most complex.

This thread keeps skirting around the interesting part of the MAP sensor and how the ECU is forced to deal with what the sensor is "seeing" in the intake.

Don't know why you would say forced to deal with. Wouldn't the code be set up and calibrations to work within it's enviroment? Then it would be normal, just different then say a 4 banger with a normal intake .
Ron