Why understanding Sensors is important

[Steve Cole]

This is just to be a discussion on Sensors Only. What they do and what they do not do. I've attached a datasheet for a MAP sensor from Delphi. This is typical of what a MAP sensor does, from all manufactures in the automotive market place. Look it over and let's have a discussion about it.

[FLTRI]

Sure would be nice to understand how the MAP sensors work in a short little common intake.
Since we know there's crosstalk it's hard for me anyway, to understand how the ECM makes it work.
Bob

[harley_cruiser]

I have read a lot about what the MAP sensor does but never found out how it does it, not sure if I could read it if I found that information but would love to know.

[whittlebeast]

Can we talk about default map, map read 1, map read 2, egr, map and how they all relate.

Andy

[akjeff]

This is just to be a discussion on Sensors Only. What they do and what they do not do. I've attached a datasheet for a MAP sensor from Delphi. This is typical of what a MAP sensor does, from all manufactures in the automotive market place. Look it over and let's have a discussion about it.

I'll take a stab at it. The MAP measures the pressure of the intake manifold, relative to ambient air. This, coupled with the intake air temp, and engine RPM help the ECM calculate the amount of air entering the intake(the VE table if you will), so it knows how much fuel to deliver, to give the AFR in the cell that most closely matches the condition at that moment in time.

Jeff

[whittlebeast]

You must keep in mind that the pressure in the intake, on a wobble fire motor is insanely dynamic.  It is this pressure change compared to the missing teeth that is used to figure out where in 720 degrees of rotation, the motor is at any given time.

A MAP sensor is way faster of a reacting device than you would think.

Andy

[joe_lyons]

Map sensor is a pressure and vac sensitive sensor.  It has a flexible silicon chip that is factory calibrated and then Dependant on its range it is able to go from close to 0 to 300 kpa.  Ours are only operable between near 0 to 100ish kpa. 

The cam tune/map tooth read is what decides where to take the read from.  This can change the readings at idle and affect your EGR table. 

Steve I just don't know if the poll of the map is taken from one to the other or is it 2 separate polls?  Could you explain to us in a little more detail when we are choosing the cam tune point what is it that we are actually seeing.  I know the procedure but just not exactly why.

[dynaglide]

I still don't understand how it actually works 

Since the pressure in the manifold is "insanely dynamic", which I take to mean "varies greatly over the course of each crankshaft revolution", how does the ignition module (I have a carbed bike...) know which of the many different pressures to use for the ignition timing?  Does the MAP sensor average the pressure over a given time?  Or does it report to the ignition module in "real time" and the module does the averaging?  And over what timeframe does it average the readings?  Once every crank rev?  Something else? 

[whittlebeast]

I am trying to locate a MAP log off a Harley at the tooth level.

[dynaglide]

are you referring to the missing tooth on the flywheel?  So I guess the ignition module correlates the MAP sensor readings with the flywheel "timing mark" (missing tooth)?  And only uses the sensor reading for that particular instance (which I assume would also be the same particular instance it uses to determine the ignition timing)?

[Steve Cole]

Please reread the title of the post and my first post. Lot's of people here trying to go beyond just understanding a sensor and so far not one of you has answered the question properly. Read the attached datasheet and lets get everyone of you up to understanding just what the sensor is, and what it can and cannot do.

[rbabos]

Please reread the title of the post and my first post. Lot's of people here trying to go beyond just understanding a sensor and so far not one of you has answered the question properly. Read the attached datasheet and lets get everyone of you up to understanding just what the sensor is, and what it can and cannot do.

Not sure what the correct answer is? To me it's nothing more then a variable resister that changes voltage output to the ECM based on manifold pressure.
Ron

[a2wheeler]

interesting that this sensor provides two outputs.
They provide two separate
outputs critical to air/fuel ratio optimization:
• One voltage output proportional to engine intake manifold
pressure
• Thermistor output proportional to manifold air temperature

[Coyote]

Please reread the title of the post and my first post. Lot's of people here trying to go beyond just understanding a sensor and so far not one of you has answered the question properly. Read the attached datasheet and lets get everyone of you up to understanding just what the sensor is, and what it can and cannot do.

Not sure what the correct answer is? To me it's nothing more then a variable resister that changes voltage output to the ECM based on manifold pressure.
Ron

There would have to of been a question first. There was none.   

[a2wheeler]

as for the goal - "understanding just what the sensor is, and what it can and cannot do."
It just provides a voltage amount that represents the kpa and the temp. That is all, it does not do anything else. Those outputs are available for other things to read and use that input for various logic processes.
There are ranges and accuracy for both outputs, and I presume it is reasonably fast at reacting to changes , and therefore the output provided is its best delivery of the current status of those two metrics.

[harley_cruiser]

Map sensor is a pressure and vac sensitive sensor.  It has a flexible silicon chip that is factory calibrated and then Dependant on its range it is able to go from close to 0 to 300 kpa.  Ours are only operable between near 0 to 100ish kpa. 

The cam tune/map tooth read is what decides where to take the read from.  This can change the readings at idle and affect your EGR table. 

Thank you Joe, that makes since.

[Steve Cole]

Please reread the title of the post and my first post. Lot's of people here trying to go beyond just understanding a sensor and so far not one of you has answered the question properly. Read the attached datasheet and lets get everyone of you up to understanding just what the sensor is, and what it can and cannot do.

Not sure what the correct answer is? To me it's nothing more then a variable resister that changes voltage output to the ECM based on manifold pressure.
Ron

There would have to of been a question first. There was none.   

OK, so I missed the "?" but others seem to have read it how I hoped "What they do and what they do not do"

I have tired to limit the discussion to just Sensors so people can learn about them. If they understand what they can and cannot do the rest of it all becomes easy to understand. The problem I see is most people really have no idea how they work or what they can and cannot do. I provided a current Delphi MAP datasheet with all the necessary information from Delphi so it can be discussed. In this case it can measure two different parameters and provide an ouput (for each)that represents the results of it's measurements. It also tells you how accurate each measurement can be and in what range. So a2wheeler is the only one who got to the first part of the question, "What they do"

[FSG]

So what is the actual question then?   Spell it out or better still edit your original post so that it is obvious.

[fbn ent]

I find this interesting. So the sensor basically measures the negative pressure in the manifold and the intake air temperature? I am assuming that we will be going through all the sensors (kinda like Preacher's Son & Professor Poop ) Anything to learn more stuff!

[whittlebeast]

All pressures are positive in the EFI world.  0 is no air, 100 is close to sea level.

[a2wheeler]

I think what is important about this sensor is that it does not tell you 0 or 100 or anything in between. It only provides a voltage. What ever is reading this voltage has to understand the value and its mapping to a range of 15 - 102kpa.

[hrdtail78]

I find this interesting. So the sensor basically measures the negative pressure in the manifold and the intake air temperature? I am assuming that we will be going through all the sensors (kinda like Preacher's Son & Professor Poop ) Anything to learn more stuff!

Might look through the sticky's and look for several topics of this nature by Steve.   Good stuff that merited a sticky.  It's always a bit bumpy in the beginning but after guys get their shots in.  They progress nicely with good info in them.

[fbn ent]

Thanks for that. LOTS of good information there.

[BVHOG]

In simply terms it measures engine load based on pressure changes.

[98fxstc]

There is a requirement for a given air/fuel ratio at operating conditions.
The air intake determines the fuel required.
Oxygen levels in air vary with temperature so we need to measure the temperature of the air
The air intake by the motor varies with load/rpm so we need to measure how much volume of air the motor is sucking in
so map sensor to measure vacuum
all sensors convert convert measurements to electrical signals (voltage,current or resistance) which are processed by the ECM
Things that come into play are the absolute accuracy of the sensors and the relative accuracy of the sensors in the range in which they are working
These sensors appear to be pretty accurate over the range in which they are working
Whether or not the ECM gets the correct information is determined by the environment in which they are working
Map , for example , whether the signals may be affected by crosstalk between the cylinders

Might be jumping the gun here , but compare these sensors with narrow band O2 sensors which are only accurate in part of the range in which they are working , and are also influenced by crosstalk between pipes , and EGR