Manifold Absolute Pressure (MAP) vs barometer when N/A

[FNBADAZ06]

Doesnt the computer adapt to the MAP reading and adjust the parameters to run at it's programed optimium running condition?

In other words if you installed a perfect MAP that was reading true, the computer would just adapt to that new reading and adjust the parameters to run at optimium again... Better or worse, your motor should run the same based on the current pressure...

I think your chasing a fictitious number here.

As long as the ECU understands the bias from the MAP sensor and makes it's adjustments in coorelation with other sensory input....you're right, it should run fine as long as that MAP reading is not so far out in left field (so to speak).

As far as the engine running "the same for better or worse", while an extreme example, what do you think happens to your fuel and timing mappings when you're driving along Pike Peak at 9,000+ feet ASL ?

The MAP readings are going to be significantly lower because of the altitude and the car's ECU adjust accordingly, right ? Less fueling, less timing, less power.....all associated with low barometric pressure when at altitude...right ?

Now, bring that same MAP reading down to sea level where the air is much denser and the car can handle greater fuel and timing values without KR.....now what ?

I'm not chasing a ficticious number, so to speak, but rather trying to understand the bias in the MAP sensor with relation to TRUE absolute barometric pressure as referenced by a weather machine. If a Manifold Absolute Pressure sensor is supposed to read Absolute Pressure, why the difference in the displayed values...as you can't take the reading shown by the logger at face value.

Much like your TPS sensor......100% throttle does not equal a value of 100.00 as it relates to the TPS sensor and shown in the logger. A reading of 88.35 (IIRC) equates to 100% commanded throttle

[HOXXOH]

Doesnt the computer adapt to the MAP reading and adjust the parameters to run at it's programed optimium running condition?

In other words if you installed a perfect MAP that was reading true, the computer would just adapt to that new reading and adjust the parameters to run at optimium again... Better or worse, your motor should run the same based on the current pressure...

I think your chasing a fictitious number here.

As long as the ECU understands the bias from the MAP sensor and makes it's adjustments in coorelation with other sensory input....you're right, it should run fine as long as that MAP reading is not so far out in left field (so to speak).

As far as the engine running "the same for better or worse", while an extreme example, what do you think happens to your fuel and timing mappings when you're driving along Pike Peak at 9,000+ feet ASL ?

The MAP readings are going to be significantly lower because of the altitude and the car's ECU adjust accordingly, right ? Less fueling, less timing, less power.....all associated with low barometric pressure when at altitude...right ?

Now, bring that same MAP reading down to sea level where the air is much denser and the car can handle greater fuel and timing values without KR.....now what ?

I'm not chasing a ficticious number, so to speak, but rather trying to understand the bias in the MAP sensor with relation to TRUE absolute barometric pressure as referenced by a weather machine. If a Manifold Absolute Pressure sensor is supposed to read Absolute Pressure, why the difference in the displayed values...as you can't take the reading shown by the logger at face value.

Much like your TPS sensor......100% throttle does not equal a value of 100.00 as it relates to the TPS sensor and shown in the logger. A reading of 88.35 (IIRC) equates to 100% commanded throttle

Correction needed: Pike's Peak elevation is 14,200'. 91 octane was overkill.

So a question I'd have is: Does that MAP reading that we checked with the engine off, change with elevation/BP or is it a constant?

[FNBADAZ06]

Doesnt the computer adapt to the MAP reading and adjust the parameters to run at it's programed optimium running condition?

In other words if you installed a perfect MAP that was reading true, the computer would just adapt to that new reading and adjust the parameters to run at optimium again... Better or worse, your motor should run the same based on the current pressure...

I think your chasing a fictitious number here.

As long as the ECU understands the bias from the MAP sensor and makes it's adjustments in coorelation with other sensory input....you're right, it should run fine as long as that MAP reading is not so far out in left field (so to speak).

As far as the engine running "the same for better or worse", while an extreme example, what do you think happens to your fuel and timing mappings when you're driving along Pike Peak at 9,000+ feet ASL ?

The MAP readings are going to be significantly lower because of the altitude and the car's ECU adjust accordingly, right ? Less fueling, less timing, less power.....all associated with low barometric pressure when at altitude...right ?

Now, bring that same MAP reading down to sea level where the air is much denser and the car can handle greater fuel and timing values without KR.....now what ?

I'm not chasing a ficticious number, so to speak, but rather trying to understand the bias in the MAP sensor with relation to TRUE absolute barometric pressure as referenced by a weather machine. If a Manifold Absolute Pressure sensor is supposed to read Absolute Pressure, why the difference in the displayed values...as you can't take the reading shown by the logger at face value.

Much like your TPS sensor......100% throttle does not equal a value of 100.00 as it relates to the TPS sensor and shown in the logger. A reading of 88.35 (IIRC) equates to 100% commanded throttle

Correction needed: Pike's Peak elevation is 14,200'. 91 octane was overkill.

So a question I'd have is: Does that MAP reading that we checked with the engine off, change with elevation/BP or is it a constant?

Somehow, I knew that elevation and still used the lower altitude

But the example I presented would still be valid.

Your other question is a valid one......my brain tells me it HAS to read differently at varying altitudes, otherwise, why even have the darn thing ?

Wiki

Manifold Absolute Pressure sensor

"The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion (see stoichiometry). A fuel-injected engine may alternately use a MAF (mass air flow) sensor to detect the intake airflow. A typical configuration employs one or the other, but seldom both."

LS engine's employ BOTH.

ab·so·lute   /ˈæbsəˌlut, ˌæbsəˈlut/ Show Spelled[ab-suh-loot, ab-suh-loot

adjective

1. free from imperfection; complete; perfect: absolute liberty.

2. not mixed or adulterated; pure: absolute alcohol.

3. complete; outright: an absolute lie; an absolute denial.

4. free from restriction or limitation; not limited in any way: absolute command; absolute freedom.

5. unrestrained or unlimited by a constitution, counterbalancing group, etc., in the exercise of governmental power, especially when arbitrary or despotic: an absolute monarch.

Our obvious conclusion from last night's test is that you can't take the MAP reading's in a literal sense, as the figures we saw in the data log were definetly NOT absolute in nature, but off by at least 5 kPa

[NicD]

There's a whole lot of discussion here so I'll just make some comments. Comparing your MAP sensor to a nice accurate weather station isn't going to do much good. The best you can do is to compare what it's reading key on engine off (or baro if it's updated) to what it reads at WOT as that will give you a good indication of how the intake system as a whole is doing in regards to efficiency. The MAP sensor is in the intake manifold after the TB so what you are seeing is the end result of how restrictive everything is in front of it (the filter, plumbing, MAF, TB, and intake for the most part). You will never see baro at WOT in the upper RPMs regardless of how efficient you make your setup as there is always some small amount of restriction, even if you remove all of it and just run open TB and have a venturi on it to help smooth airflow going in. There are always inefficiencies in the intake, etc to some degree. For all intensive purposes since your car is still MAF based (ignoring the blend) it will have the final say on airflow calculations so when you go up/down in elevation or the weather changes it will compensate accurately. The map sensor is used more so in speed density where it's using pre-programmed lookups to calculate fueling and load calcs for timing.

[HOXXOH]

Doesnt the computer adapt to the MAP reading and adjust the parameters to run at it's programed optimium running condition?

In other words if you installed a perfect MAP that was reading true, the computer would just adapt to that new reading and adjust the parameters to run at optimium again... Better or worse, your motor should run the same based on the current pressure...

I think your chasing a fictitious number here.

As long as the ECU understands the bias from the MAP sensor and makes it's adjustments in coorelation with other sensory input....you're right, it should run fine as long as that MAP reading is not so far out in left field (so to speak).

As far as the engine running "the same for better or worse", while an extreme example, what do you think happens to your fuel and timing mappings when you're driving along Pike Peak at 9,000+ feet ASL ?

The MAP readings are going to be significantly lower because of the altitude and the car's ECU adjust accordingly, right ? Less fueling, less timing, less power.....all associated with low barometric pressure when at altitude...right ?

Now, bring that same MAP reading down to sea level where the air is much denser and the car can handle greater fuel and timing values without KR.....now what ?

I'm not chasing a ficticious number, so to speak, but rather trying to understand the bias in the MAP sensor with relation to TRUE absolute barometric pressure as referenced by a weather machine. If a Manifold Absolute Pressure sensor is supposed to read Absolute Pressure, why the difference in the displayed values...as you can't take the reading shown by the logger at face value.

Much like your TPS sensor......100% throttle does not equal a value of 100.00 as it relates to the TPS sensor and shown in the logger. A reading of 88.35 (IIRC) equates to 100% commanded throttle

Correction needed: Pike's Peak elevation is 14,200'. 91 octane was overkill.

So a question I'd have is: Does that MAP reading that we checked with the engine off, change with elevation/BP or is it a constant?

Somehow, I knew that elevation and still used the lower altitude

But the example I presented would still be valid.

Your other question is a valid one......my brain tells me it HAS to read differently at varying altitudes, otherwise, why even have the darn thing ?

Wiki

Manifold Absolute Pressure sensor

"The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion (see stoichiometry). A fuel-injected engine may alternately use a MAF (mass air flow) sensor to detect the intake airflow. A typical configuration employs one or the other, but seldom both."

LS engine's employ BOTH.

ab·so·lute   /ˈæbsəˌlut, ˌæbsəˈlut/ Show Spelled[ab-suh-loot, ab-suh-loot

adjective

1. free from imperfection; complete; perfect: absolute liberty.

2. not mixed or adulterated; pure: absolute alcohol.

3. complete; outright: an absolute lie; an absolute denial.

4. free from restriction or limitation; not limited in any way: absolute command; absolute freedom.

5. unrestrained or unlimited by a constitution, counterbalancing group, etc., in the exercise of governmental power, especially when arbitrary or despotic: an absolute monarch.

Our obvious conclusion from last night's test is that you can't take the MAP reading's in a literal sense, as the figures we saw in the data log were definetly NOT absolute in nature, but off by at least 5 kPa

I'd ask on CF if a high altitude and a sea level member would do the test we did. If they both read real close to the same, then it's a constant that's not activated with the engine off and we can quit being confused anymore than we already are.

[NicD]

Map readings always change with altitude and air density. On a warm day here in phoenix it will show around 96 to 97 vs when its cold will show 99 but I've never seen 100. Up in payson I've seen 94.

[FNBADAZ06]

Map readings always change with altitude and air density. On a warm day here in phoenix it will show around 96 to 97 vs when its cold will show 99 but I've never seen 100. Up in payson I've seen 94.

We saw 95 and 96 last night with ignition keyed and engine off, with cool air and a weather baro of 30.06.

I was suprised to see a 5+ kPa difference between actual and MAP, when I would've expected 98+...and no knowledge of what or why

Now that I see that it has little value in monitoring, other than confirming that the engine off kPa value and the WOT kPa value are close, I guess there's no other reason to continueing monitoring/viewing it in my scans/logs.

[NicD]

Map readings always change with altitude and air density. On a warm day here in phoenix it will show around 96 to 97 vs when its cold will show 99 but I've never seen 100. Up in payson I've seen 94.

We saw 95 and 96 last night with ignition keyed and engine off, with cool air and a weather baro of 30.06.

I was suprised to see a 5+ kPa difference between actual and MAP, when I would've expected 98+...and no knowledge of what or why

Now that I see that it has little value in monitoring, other than confirming that the engine off kPa value and the WOT kPa value are close, I guess there's no other reason to continueing monitoring/viewing it in my scans/logs.

I guess I'm not sure how it could show only 95 kpa last night, what does the baro pid read in the scanner? This time of year at night all I ever see is around 98-99 kpa KOEO and the most efficient cold air intakes, etc only drop a couple of KPA at high RPM WOT.

There is still value in monitoring that pid so I would still log it since it's still a good reference at other points like at part throttle as well.

[FNBADAZ06]

Map readings always change with altitude and air density. On a warm day here in phoenix it will show around 96 to 97 vs when its cold will show 99 but I've never seen 100. Up in payson I've seen 94.

We saw 95 and 96 last night with ignition keyed and engine off, with cool air and a weather baro of 30.06.

I was suprised to see a 5+ kPa difference between actual and MAP, when I would've expected 98+...and no knowledge of what or why

Now that I see that it has little value in monitoring, other than confirming that the engine off kPa value and the WOT kPa value are close, I guess there's no other reason to continueing monitoring/viewing it in my scans/logs.

I guess I'm not sure how it could show only 95 kpa last night, what does the baro pid read in the scanner? This time of year at night all I ever see is around 98-99 kpa KOEO and the most efficient cold air intakes, etc only drop a couple of KPA at high RPM WOT.

There is still value in monitoring that pid so I would still log it since it's still a good reference at other points like at part throttle as well.

I guess I'm not a schooled in tuning and reading HP Tuners screens, Nic.

I looked at the iRev screen for my car and HP Tuners Pro on the guage screen and it showed 96 kPa for both programs. I went to Tom (HOXXOH) houses and looked at the readings from his LS3 and we saw 95 kPa. Tom had a physical weather station in his garage and saw 30.06. Are we not looking at the data properly ? I'll let Tom add any additional data or if he has a differenet few on what we saw.

[Two Fangs]

My car is 99 right now.... But it is running a 2.5 BAR sensor that has had the Linear and Offset scaled in the tune.

[FNBADAZ06]

I'm thinking of hitting Speedworld tonight, so I'll log the runs for review and see what the MAP readings are Anyone else want to go and help me decipher what the logs are saying ?

[FNBADAZ06]

Map readings always change with altitude and air density. On a warm day here in phoenix it will show around 96 to 97 vs when its cold will show 99 but I've never seen 100. Up in payson I've seen 94.

We saw 95 and 96 last night with ignition keyed and engine off, with cool air and a weather baro of 30.06.

I was suprised to see a 5+ kPa difference between actual and MAP, when I would've expected 98+...and no knowledge of what or why

Now that I see that it has little value in monitoring, other than confirming that the engine off kPa value and the WOT kPa value are close, I guess there's no other reason to continueing monitoring/viewing it in my scans/logs.

I guess I'm not sure how it could show only 95 kpa last night, what does the baro pid read in the scanner? This time of year at night all I ever see is around 98-99 kpa KOEO and the most efficient cold air intakes, etc only drop a couple of KPA at high RPM WOT.

There is still value in monitoring that pid so I would still log it since it's still a good reference at other points like at part throttle as well.

Nic or Mike.....what exactly the does highlighted statement in Nic's post mean ?

Other than selecting the MAP guage and changing the displayed values to kPa, is there something else I should be doing to the configuration ?

[Two Fangs]

Hey Victor, in HP Tuners we can actually log BARO. This PID comes from an algorithm that measures MAP before startup (same thing as BARO, if the engine isn't running) and compares it to the MAP and MAF signals with the engine running to virtually determine atmospheric pressure. Many things done on these PCMs are done with algorithms, from catalyst temperature to spark smoothing. Most of this data determined through the use of algorithms is probably not available on a more generic-type scanner. Hope this helps. Parker

[FNBADAZ06]

Hey Victor, in HP Tuners we can actually log BARO. This PID comes from an algorithm that measures MAP before startup (same thing as BARO, if the engine isn't running) and compares it to the MAP and MAF signals with the engine running to virtually determine atmospheric pressure.

Many things done on these PCMs are done with algorithms, from catalyst temperature to spark smoothing.

Most of this data determined through the use of algorithms is probably not available on a more generic-type scanner. Hope this helps.

Parker

OK....I'm guessing there's a special config I would need to setup to measure BARO, as there's no default config in HP Tuner that already has this setup ?

edit: I guess my original question for this thread got answered.....that the MAP readings in it's raw form, regardless if it uses the same measuring unit as a weather station, is NOT a comparable number to TRUE barometric pressure.

[Two Fangs]

Yeah, it is just a regular old PID in HPT. Go to the Table view in the scanner. Right click on an empty line. Click insert from the menu that appears. Under PID List, select Engine>Airflow>Barometric Pressure and voila, you are all set!

[FNBADAZ06]

Yeah, it is just a regular old PID in HPT.

Go to the Table view in the scanner.

Right click on an empty line.

Click insert from the menu that appears.

Under PID List, select Engine>Airflow>Barometric Pressure and voila, you are all set!

SWEET !!!!!! I'll do it....thanks for the help again, bud

I'll go out and test it right away and report back what it says.

[Two Fangs]

Once you are logging it in the table, you can make a gauge, or add it to the graph, or make a histo. Whatever you want. Since it doesn't really change much, I just keep it in the table for reference.

[FNBADAZ06]

Once you are logging it in the table, you can make a gauge, or add it to the graph, or make a histo. Whatever you want.

Since it doesn't really change much, I just keep it in the table for reference.

Weird....the ability to insert into the table is greyed out.

Is there a limit to how many items that can be listed in the table at one time, i.e. do I need to remove one of the pre-existing items before adding a new one ?

[Two Fangs]

If there is a line in the table open, it should not be a problem at all. Let me do a little checking....

[FNBADAZ06]

If there is a line in the table open, it should not be a problem at all.

Let me do a little checking....

K.

You can call me as well if it's prefereable instead of posting in the thread.

[Two Fangs]

Victor, are you trying to do it while you are scanning? It won't let you then. Try to add it while the VCM is not connected to the PC and let me know. Thanks

[FNBADAZ06]

Victor, are you trying to do it while you are scanning? It won't let you then. Try to add it while the VCM is not connected to the PC and let me know.

Thanks

Nope....netbook is sitting in front of me at the kitchen countertop without the VCM attached.

edit: never mind.....the instance of VCM Scanner was from my other night when I logged SLAMMER's car....the computer then went into sleep mode. Comingout of sleep mode the VCM instance restarted from that night.

I shutdown VCM Scanner application and restarted it from scratch and can now add the PID

Now I just need to read on how to add it to the graph or make a guage for it

[Two Fangs]

Glad you got it figured out! Give a post, shout or a text if you need anything else.

[FNBADAZ06]

Glad you got it figured out!

Give a post, shout or a text if you need anything else.

You are DA MAN !!!!!

thanks for the help this morning, bud

[HOXXOH]

I'm thinking of hitting Speedworld tonight, so I'll log the runs for review and see what the MAP readings are

Anyone else want to go and help me decipher what the logs are saying ?

I'm pretty sure I'll go tonight too. I'll get my pid set for baro now and we can compare results.