Sensed map - what does it do?

[spoolboy]

I've seen that sensed map is normally disabled in the factory tunes, but it is often enabled by tuners.

What does it do? I see it has a PR threshold which is usually around .9x - just under atmospheric - pretty high load/WOT.

[Mattechperf]

Someone please correct me if I'm wrong, but I believe the Sensed MAP is to establish a baseline air pressure when the Baro Learn is disabled.
The difference is the Sensed MAP updates the value on each key start, but the Baro Learn does it constantly during operation.

In stock form, the Baro Learn constantly updates atmospheric pressure with a separate sensor to account for elevation changes.

I believe by disabling the Baro Learn it locks in the air pressure variable so you're not constantly changing the tune based on inconsistent data logs.

[spoolboy]

Found this old thread:

https://forum.hptuners.com/showthrea...ble-or-Disable

[Mattechperf]

Found this old thread:

https://forum.hptuners.com/showthrea...ble-or-Disable

Ahhh, there's some good info.
Thanks for posting that.

[B00STJUNKY]

Someone please correct me if I'm wrong, but I believe the Sensed MAP is to establish a baseline air pressure when the Baro Learn is disabled.
The difference is the Sensed MAP updates the value on each key start, but the Baro Learn does it constantly during operation.

In stock form, the Baro Learn constantly updates atmospheric pressure with a separate sensor to account for elevation changes.

I believe by disabling the Baro Learn it locks in the air pressure variable so you're not constantly changing the tune based on inconsistent data logs.

While I don't have any proof to back it up, it's my understanding that "Baro Learn" and "Sensed MAP" are completely independent of each other.

Baro Learn is something that works using MAP sensor readings at times when it can safely be assumed that manifold pressure should be equal to atmospheric pressure (think in scenarios where there is a large throttle opening at relatively low RPM; and thus very little airflow requirements exist; that would result in intake manifold pressure likely being equal to atmospheric pressure).

There are some cases, though they seem only to be present on vehicles that come from the factory with forced induction, where there is a separate pressure sensor (in the case of the SRT-4 platform, called a TIP sensor, or Throttle Inlet Pressure Sensor) so that it can measure atmospheric pressure without any risk of a false reading being brought on by super/turbo chargers creating positive pressure at sampling intervals.

As an aside, this TIP sensor on the SRT-4 is plumbed through a 3 port solenoid that allows the sensor to read atmospheric pressure directly off of the solenoid port through a small cloth filter, and through the other port allows it to read pressure in the charge pipe just before the throttle body. Hence "Throttle Inlet Pressure Sensor".

As far as Sensed MAP, I don't have much of anything to add beyond what was linked in the other thread.

All this to say, they operate independently of each other. You can have any combination of one or the other enabled/disabled, and they don't necessarily affect each other.

In cases of vehicles that don't have a separate pressure sensor to measure atmospheric pressure and have had a turbo or supercharger added, it is a good idea to disable Baro Learn so that it doesn't learn the wrong pressure due to turbo/supercharger pressure interference.

[Mattechperf]

There are some cases, though they seem only to be present on vehicles that come from the factory with forced induction, where there is a separate pressure sensor (in the case of the SRT-4 platform, called a TIP sensor, or Throttle Inlet Pressure Sensor) so that it can measure atmospheric pressure without any risk of a false reading being brought on by super/turbo chargers creating positive pressure at sampling intervals.

That makes more sense. After thinking about it, I'm pretty sure the Hemi cars (and probably all N/A cars) don't have a baro sensors like I remember on the old Turbo Dodge 4cyl cars.
And yes, boosted setups seem to be recommended to disable Baro Sense.

[Homer]

Hey guys, these workbooks from FCA give a little insight as to how map readings are handled by the PCM. Just open the PDFs and do a search for T-MAP (map calculated base off throttle and other inputs). Basically the PCM uses calculated map to handle the delay in MAP readings.

https://www.challengertalk.com/forum...5&d=1550198450
https://www.challengertalk.com/forum...3&d=1550286255

BTW this is a pretty good description of MAP operation.
https://forum.hptuners.com/showthrea...l=1#post519561

[spoolboy]

That makes more sense. After thinking about it, I'm pretty sure the Hemi cars (and probably all N/A cars) don't have a baro sensors like I remember on the old Turbo Dodge 4cyl cars.
And yes, boosted setups seem to be recommended to disable Baro Sense.

Speaking of those old TD cars, of which I had more than a couple....

If you hooked your boost gauge into the map sensor vacuum line, you would occasionally see the gauge go to 0 and back really quickly as the barometric pressure solenoid (3 way vacuum solenoid) would get a baro sample while driving. Took me a while to figure out what was going on.

The early efi Dodge cars had the map in the ecm in the interior kick panel. As years went by the MAP sensor was moved closer and closer to the intake manifold until the Neons finally got the sensor screwed right into the manifold, where it has stayed.

[Homer]

Apparently there is a controller "8GMx" (1.4L turbo) that has the baro sensor integrated on the controller itself.
8GMx.JPG

[spoolboy]

Apparently there is a controller "8GMx" (1.4L turbo) that has the baro sensor integrated on the controller itself.
8GMx.JPG

Learn something new every day! Guess that's the Dart/Renegade engine?

[06300CSRT8]

Think of it this way. The ECU has two sources of a MAP reading, a calculated MAP based on VE and engine size, or actual MAP from the sensor. Most ECUs have a switching point, as well, to move from calculated to actual map. The ECU also stores an "Average MAP" which ultimately is what is used for final fueling. The input to the Average MAP is what you are changing with that switch.

The naming convention always messed me up, if I recall correctly sensed map is the calculated value, i.e. what the ECU "thinks" you should be seeing for a MAP value. Disabling this feature means the ECU always just applies fueling based on the actual sensor, without any modeling. This is the easiest way to get fueling to follow commanded EQ ratio but has the pitfalls with a radical cam that has oscillating map values to result in radical fuel trims. Using sensed map in lower rpms usually has much upside.

I have seen issues where lchanging sensed map from the factory setting resulted in the ECU never going into open loop under full throttle / boost. And I have seen it both ways, usually its going from disabled to enabled, but for my 2014 Chrysler (GPEC2) I went from factory enabled to disabled and never could get open loop fueling, so I went back to enabled and never looked back.

[Homer]

The naming convention always messed me up, if I recall correctly sensed map is the calculated value, i.e. what the ECU "thinks" you should be seeing for a MAP value. Disabling this feature means the ECU always just applies fueling based on the actual sensor, without any modeling. This is the easiest way to get fueling to follow commanded EQ ratio but has the pitfalls with a radical cam that has oscillating map values to result in radical fuel trims. Using sensed map in lower rpms usually has much upside.

I thought sensed map disabled (usually disabled in stock tunes) meant the PCM uses calculated values and enabling it allows the PCM to go off measured MAP readings. In fact, in most FI tunes I have seen have sensed MAP enabled with a Pratio threshold of >0.9.
https://forum.hptuners.com/showthrea...l=1#post519561


I think you got it backwards, a while back you said sensed MAP was actual sensor reading.
https://forum.hptuners.com/showthrea...l=1#post388134

[06300CSRT8]

I thought sensed map disabled (usually disabled in stock tunes) meant the PCM uses calculated values and enabling it allows the PCM to go off measured MAP readings. In fact, in most FI tunes I have seen have sensed MAP enabled with a Pratio threshold of >0.9.
https://forum.hptuners.com/showthrea...l=1#post519561

Yea I noted i forget the direction. Its a misnomer to be honest, because in older ECUs setting it to "disabled" still allowed it to enable under the pratio threshold, but we just didn't have the pratio threshold mapped out for us by HP Tuners.

So how I have seen it behave,

Disabled - means it is enabled below pratio threshold, disabled above
Enabled - means enabled below pratio threshold as well as above it.

It doesn't entirely disable it from what I have observed. To know for sure, a log of your airflow will show blips from your max airflow in your diag engine tab up to a much larger actual reading during a log on a vehicle in boost. That will confirm it is ENABLED.

[spoolboy]

I read this about 7 times and I think I'm finally getting it.

If you call "sensed map" "alpha N", then it makes a lot more sense to me.

The pratio thresh is the pratio to switch to using "alpha N" or a predicted map instead of actual. Airflow is calculated by throttle position and RPM only - actual map is not really used.

"Enable" means "gimmie alpha N all the time". Disabled means "alpha N" only above pratio thresh setting.

Or am I still confused?

[Homer]

This is good stuff, I need to test this out this weekend. What I found interesting is the tuning school actually enables sensed map in their FI section and sets the threshold to 0.00, the PCM was a GPEC2A. I have only tried it this way and must say pedal response felt muy bueno when blipping the throttle but idle was not as smooth and there was a slight hesitation around 2krpm if I moderately increased the throttle.

[B00STJUNKY]

I read this about 7 times and I think I'm finally getting it.

If you call "sensed map" "alpha N", then it makes a lot more sense to me.

The pratio thresh is the pratio to switch to using "alpha N" or a predicted map instead of actual. Airflow is calculated by throttle position and RPM only - actual map is not really used.

"Enable" means "gimmie alpha N all the time". Disabled means "alpha N" only above pratio thresh setting.

Or am I still confused?

It would sure be good to find some conclusive evidence for one way or the next. I fully understand what you're referencing when you say Alpha N. It's a bit like what the above provided documentation refers to as T-MAP (Throttle MAP - where throttle position vs RPM generates an assumed or calculated MAP value).

My understanding of Sensed MAP from what most have agreed upon in the past is that it is actual MAP sensor readings (rather than T-MAP). But just a few posts up, 06300SRT8 made it sound like it was the opposite, though I think he may have tried to correct that in his later post when he said "Yea I noted i forget the direction."

The fact that most FI tunes resort to Sensed MAP would indicate to me that Sensed MAP is actual MAP sensor values, rather than relying upon a pre-defined/calibrated T-MAP table that would likely be horribly inaccurate for a heavily modified vehicle, especially one with forced induction.

[Homer]

The fact that most FI tunes resort to Sensed MAP would indicate to me that Sensed MAP is actual MAP sensor values, rather than relying upon a pre-defined/calibrated T-MAP table that would likely be horribly inaccurate for a heavily modified vehicle, especially one with forced induction.

My final tune with Arrington still had sensed MAP disabled and threshold set at 0.96 (all stock setting) the car ran fine which suggests sensed map "disabled" may use T-MAP below the threshold and actual MAP above. I have still have a slight surge at moderate pedal travel which has me wondering if it could be the switch from T-MAP to actual MAP that is causing it (assuming that's how it works)? Usually folks say the fix to surge is tweaking the air tables but is it truly necessary when you always run off actual MAP (i.e. threshold set to 0.00)? I just quickly ran through the tuning school book (FI section) and really the only air table in the throttle section that is messed with is the start-up.

I wish spring was here because I have my tune modified to try the tuning school way. All this snow and salt is killing me.

[spoolboy]

It would sure be good to find some conclusive evidence for one way or the next. I fully understand what you're referencing when you say Alpha N. It's a bit like what the above provided documentation refers to as T-MAP (Throttle MAP - where throttle position vs RPM generates an assumed or calculated MAP value).

My understanding of Sensed MAP from what most have agreed upon in the past is that it is actual MAP sensor readings (rather than T-MAP). But just a few posts up, 06300SRT8 made it sound like it was the opposite, though I think he may have tried to correct that in his later post when he said "Yea I noted i forget the direction."

The fact that most FI tunes resort to Sensed MAP would indicate to me that Sensed MAP is actual MAP sensor values, rather than relying upon a pre-defined/calibrated T-MAP table that would likely be horribly inaccurate for a heavily modified vehicle, especially one with forced induction.

I'm looking a tune done by a pro on a boosted 6.4 where sensed map is enabled and the thresh is 2.00. This car has a 2 bar map and NN is enabled.

[spoolboy]

I think figuring out the TMAP multiplier tables might be insightful.

Rolling this around in my head, the reason for the "TMAP" or calculated MAP is due to response time. So I see this as a part throttle strategy more than a WOT strategy, since MAP is constant at WOT and fluctuating a lot during part throttle driving. So calculated at lower kpa and actual at higher kpa makes some sense from that perspective.

[Homer]

Was messing around with the car this morning...enabled sensed MAP and kept the threshold at 0.96 and car runs like it did with sensed MAP disabled. Now if I change threshold to 0.00 like the tuning school shows, the idle suffers and there is a slight hesitation when you stomp the pedal. I only get a few options to log MAP (SAE), Sensed, Calculated and TMAP. Of all the PIDs TMAP is waaay off and SAE seems to lag just a touch behind sensed and calculated. I have a separate MAP sensor that I can log through Innovate's Logworks which I want to compare with the other PIDs to see what's up.

MAP.JPGchannels.JPG