Barometer Update Parameters

[Tick]

It doesn't look like something that updates to me at key on and when going wot....it looks like a live reading of vac/boost until it pegs at 121 kpa. Kpa was climbing on the baro right along with the map up to 121.

[Tick]

Here is the pinout for the MAF sensor I pulled from Alldata. Also, the 5 volt return is shared with the IAT....so you'd need to tie into that wire not just cut and re-route it.

[DSteck]

Here is your verification straight out of SI. .

What if I told you that SI had a habit of being wrong? I've found that more than once. One of those instances is an incorrect pin labeling on the input speed sensor for a 4L80 on one of the Express vans. I've found other wiring inaccuracies in there too.

The reading is a live reading directly from the TIAP in the MAF.

I don't really care what some bulletin says... when the charge pipe sees boost while the manifold is still in vacuum the BARO sensor updates up. Hence the reading is NOT coming from the MAP sensor.

This b

Why would you be reading boost at the maf sensor?

On anything besides a PD blower, the MAF is always on the pressurized end of the compressor.

[Road]

Learn something new everyday. Doesn't surprise me that GM service info is wrong seams to be the norm any more. I learn a lot from ya'll thanks.

[DSteck]

It's unfortunate that it's not reliable. The wiring diagrams that are wrong are the most frustrating part for me.

[DSteck]

I've got these ready. They come with the LS9 MAP and IAT. I may build them in the future with a pressure sensor integrated and hidden within the harness. These current ones are intended to have the LS9 stuck in the manifold, then plug the factory sensor into the connector on the breakout and let it hang in the engine bay.

[Redline MS]

This discussion has not quite settled my mind yet. so....we grabbed a supercharged C7 from the shop at the end of the day and started poking around.. For starters we don't see why the "baro" value has any impact on the MAP-BARO reference they are using for load. There is another PID that is actually baro which we believe is the PID that is used. The max value of 121 is because the sensor is maxed at 3.98 volts.. would be interesting to have a bigger sensor and see a higher MAP reading but no way to scale that baro from what I can see.

Also it may not be a true "measured baro" but may use both IAT and humidity combined with say MAF to back calculate that value. I have seen GM go to a lot of back door math and "models" (kind of like IVT and catalyst) with SERIES 11 controllers like the E92.

The long and short is this is how this all is weighted;

Engine torque is requested from the driver (or some other torque intervention..ie traction control, etc). This torque request is then inserted into an inverse APC (air per cylinder) based torque model in order to calculate a desired APC. This desired APC is then inserted into a desired MAF calculation, which determines desired MAF through the throttle body.

The original torque request from the controller is also inserted into an inverse MAP based torque model to calculate a desired MAP. Desired MAP and Baro are used to calculate the desired pressure difference across the throttle blade for whats called the "compressible flow calculation". This is the basis behind how ETC control works....FYI.

The pressure difference, air density, and desired MAF are then used in the desired area calculation using compressible flow. The compressible flow equation is used to calculate a desired throttle area. The desired throttle area is then given to the engine controller, which in turn opens the throttle body to achieve a desired area.....loose anybody yet?

Engine torque is calculated using measured APC and the "over our head" polynomial APC based torque equation.

The torque estimate is compared to the original torque request from the controller. If they are both equal the system is functioning correctly and the torque request will not be adjusted. If they are not equal, a torque error is calculated and a closed loop gain, steady state flags and filters are used to correct the error while controlling response time,overshoot and oscillation....this is where PID loops become handy in understanding!

The desired APC is also sent to stuff like the cam phaser (which actually has been broken apart from the torque control) as well as algorithm for the trans.....hmm....wonder why so many A8 trannys are shifting weird after a blower is installed.....

Based upon this reality I don't see how the BARO function in the MAF is a big issue....I do think going to a multiple BAR primary MAP sensor is....

I think whats important is nailing the torque model...which is not easy task without some Metlab tools... or being very creative.

HT

[DSteck]

How are you going to accurately calibrate the VE when the pressure ratio is not right because the barometric pressure is reported incorrectly? On two separate 2015 vehicles, I tried NA-MAP mode and baro was still improperly reported after entering boost (using LS9 MAP in the intake manifold).

Barometric pressure still gets used to help determine what the intake manifold pressure should be. If barometric pressure is 20-30kPa lower than it is being reported, the ECM is going to arrive at an incorrect throttle position and rely on the control loop to correct it.

You're kinda talking pitching strategies while we are talking about batting averages.

[Redline MS]

How are you going to accurately calibrate the VE when the pressure ratio is not right because the barometric pressure is reported incorrectly? On two separate 2015 vehicles, I tried NA-MAP mode and baro was still improperly reported after entering boost (using LS9 MAP in the intake manifold).

Barometric pressure still gets used to help determine what the intake manifold pressure should be. If barometric pressure is 20-30kPa lower than it is being reported, the ECM is going to arrive at an incorrect throttle position and rely on the control loop to correct it.

You're kinda talking pitching strategies while we are talking about batting averages.

That's good I like baseball. I agree that the baro is needed. My statement was that there are several pids that reference baro....some are actual some are calculated. Actual makes sense as its probably determined with key on and may also use IAT and humidity to correct it...Once is determined I see not reason it needs to be adjusted while driving. However if its used as a inlet pressure sensor ( a form of a baro's use) then I would believe its used for diagnostic and/or the pressure drop across the blade.

I'm still trying to rationalize the different types of MAP configurations and what is happening behind the scenes with the different settings. Who really knows when we select a given MAP config how it weighs the calculated values.

[DSteck]

On Gen IV, vehicles that aren't equipped with a dedicated barometric pressure sensor use the MAP sensor to determine baro, and it samples again every time the vehicle sees wide open throttle. HP Tuners silently disables this update in their enhanced operating system. If you log barometric pressure on a boosted E38, you'll see it go to 105kPa after entering boost. Same thing happens on C7s in NA-MAP mode from what I can tell. I even saw baro register as low as 90kPa in that mode... And it changed while just driving! It'll go up in boost though. When left in factory mode without the sensor broken out, it goes higher and throws off pressure ratio.

Using a dedicated sensor hanging in the engine bay and staying in factory mode results in a constant and stable baro value for the ECM to use. This was why I made the breakout and why I wired one up on the first C7 I did. It was impossible to redo the GMVE coefficients otherwise.

[Redline MS]

On Gen IV, vehicles that aren't equipped with a dedicated barometric pressure sensor use the MAP sensor to determine baro, and it samples again every time the vehicle sees wide open throttle. HP Tuners silently disables this update in their enhanced operating system. If you log barometric pressure on a boosted E38, you'll see it go to 105kPa after entering boost. Same thing happens on C7s in NA-MAP mode from what I can tell. I even saw baro register as low as 90kPa in that mode... And it changed while just driving! It'll go up in boost though. When left in factory mode without the sensor broken out, it goes higher and throws off pressure ratio.

Using a dedicated sensor hanging in the engine bay and staying in factory mode results in a constant and stable baro value for the ECM to use. This was why I made the breakout and why I wired one up on the first C7 I did. It was impossible to redo the GMVE coefficients otherwise.

I'm following your explaination. So if the MAP sensor is also acting as the BARO at WOT to establish a static baro reference then what is the BARO reading from the MAF contributing to? Also we know that BARO doesn't vary to much after a car is started (unless its going straight up Mount Everest) so which BARO is being used in the MAP-BARO calc for load? There is also a calculated BARO reading as well in the controller.

I'm not trying to debunk your explanation but rather trying to follow the string it follows to get to where it gets used into the final torque calculation.

[DSteck]

Only cars that don't use a dedicated baro sensor use the actual sensor in the intake manifold to generate a baro value (like an E38 2010 Camaro).

In NA-MAP-TIAP, the ECM uses the TIAP in the MAF to determine barometric pressure.

In NA-MAP, the ECM uses the intake manifold MAP sensor to determine baro, and seems to update every time the car sees boost. It definitely actively rechecks.

I suppose that technically, when breaking out the TIAP and using it as a baro sensor, the mode needs to be set to NA-MAP-BARO and allow the ECM to calculate TIAP, although doing so would result in scenarios where the TIAP is actually above barometric pressure (since it's after the compressor), but the ECM wouldn't realize that and probably would assume that TIAP is still about the same as barometric. Ultimately, the same thing happens in NA-MAP-TIAP mode, and you can't really have TIAP and baro be completely accurate because the ECM doesn't understand that there's a compressor in front of the throttle body. It may be possible to add another pressure transducer to AAP2 and configure it as TC-TIAP-BARO (in which case you wouldn't break out the TIAP, but instead would wire a baro sensor into AAP2), but I've never tested this.

If baro is wrong, then pressure ratio is wrong, which means GMVE calculations will be wrong as well as calculated throttle positions. Breaking out the pressure sensor is more intended to correct GMVE calculations more than anything.

[Redline MS]

Here is something we just checked. Logged a boosted car with MDI which reports "calculated baro" which HPT does not have a PID for. Even though the HPT pid for BARO will show 121 as a max, the calculated PID only goes to 108 max but changed a few times between 102-108 as it was updating. Obviously there is a limit table somewhere.

The question I have is that if you relocate the baro sensor (well really throttle inlet air pressure sensor) which is located in the MAF, it would reason that you now loose the ability to look at the pressure drop across the blade which is part of the equation I outlined in that prior post. Also if the MAP-BARO "calc" for GMVE load referencing is using the "calculated baro", as opposed to the measured baro we can log with HPT, you are looking at a possible error of only 5-6% which is error (that none of us want) but not an error to shatter the world.

I am totally for getting all this sorted out as most certainly the LT1 based cars are not really happy in processing boost between the one bar MAP and this Baro discussion. Even the HPT document that explains the MAP sensor configurations seems a bit misleading as you would think the LT4 would have a sensor starting out with SC NOT NA.....maybe is a software reporting error...

Thoughts...

[Higgs Boson]

Is this mod necessary on the LT4? I don't think so.

Does an otherwise stock LT1 with a supercharger report an exaggerated Baro reading under boost? Yes.
Does it report MAP/BARO properly with the sensor broken out of the MAF and an LS9 MAP sensor in the intake manifold? Yes....or Yes?

If yes, then what's the discussion about?

[DSteck]

This is irrelevant for the LT4. The main point is being able to maintain the proper GMVE calculations. The throttle calculations are secondary in my opinion. Obviously putting the LS9 sensor in the intake manifold is necessary. That's not really the topic at hand. The main point is correcting the GMVE. I noticed a better return to idle after breaking out the pressure transducer on both cars I did it on.

[Redline MS]

Is this mod necessary on the LT4? I don't think so.

Does an otherwise stock LT1 with a supercharger report an exaggerated Baro reading under boost? Yes.
Does it report MAP/BARO properly with the sensor broken out of the MAF and an LS9 MAP sensor in the intake manifold? Yes....or Yes?

If yes, then what's the discussion about?

The discussion became about the string of where the information goes and what parts of the controller use what for what. The one thing I've learned over the years with OEM controls like this is that it just doesn't stop where you think. We might be smart guys but the reality is there are others that know more about how this is all processed. We have just enough control to get by vs. really being on control. I've seen the back side of this with ETAS/INCA (the native development software) and we aren't even close to being in the control we would like. I got into this thread because I have parts of how this works and parts I want to see how others are viewing it. It was also geared towards LT1 based vehicles

[Road]

I understand adding the baro sensor is required to properly calibrate VE etc... But I am confused as why on a LT4 hp tuners software shows the map config as NA-MAP-Baro when in all reality you would think it would be set to SC-MAP-SCIAP-TIAP. Also taking the TIAP sensor out of the equation on LT1 make me think the ecm would loose its abillty to properly caculate torque which in return would snowball into all torque related controls. DSteck did you encounter any changes in torque control equations when taking TIAP out of the loop?

[DSteck]

When the torque model really matters for most people (for idle control), TIAP and barometric pressure are typically equal anyway. The bypass valve is going to bleed off any positive pressure that the supercharger might be making at idle. By having TIAP always register as 99kPa (give or take depending on your altitude), it ends up pretty steady. When I wasn't using a broken out sensor, baro readings updated frequently but not instantly and would tend to hang on the positive pressure end of things. With it broken out, baro remains nice and steady, and I didn't have any trouble with idle control. Actually, after properly calibrating the GMVE with the broken out sensor, the factory speed control reserve settings were able to control idle properly without running lots of throttle and low timing.

Let's face it... Aside from just wanting things to be 100% correct, do we really care that TIAP isn't registering boost when the intake manifold is? We still are able to get full throttle. It's not perfect, but it's better than leaving it be.

[NYLS1346]

im sure the fun is just beginning, and theres certain things we'll never see... i just cant wait to see what next after the e92 lol

[yellz06]

Dave, you have the correct approach, forget about what everyone else says no matter what data they might have that they can't interpret.