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Thread: Barometer Update Parameters

  1. #41
    Senior Tuner LSxpwrdZ's Avatar
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    He may be on to something though. HPT isn't scanning everything to do with Barometric Pressure, it's logging the physical sensor. However using a snap on scan tool there is another PID called Calculated Barometric Pressure and it is not updating with boost like the live reading is. Which makes me wonder if there really is anything wrong with just leaving the MAF and Baro setup the way it is...
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  2. #42
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by LSxpwrdZ View Post
    He may be on to something though. HPT isn't scanning everything to do with Barometric Pressure, it's logging the physical sensor. However using a snap on scan tool there is another PID called Calculated Barometric Pressure and it is not updating with boost like the live reading is. Which makes me wonder if there really is anything wrong with just leaving the MAF and Baro setup the way it is...
    If we are tuning without Calculated Barometric Pressure and Pressure Ratio in the VVE Editor is based on the physical sensor, is it still ok to leave the MAF and Baro setup the way it is?

  3. #43
    Senior Tuner LSxpwrdZ's Avatar
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    Quote Originally Posted by Higgs Boson View Post
    If we are tuning without Calculated Barometric Pressure and Pressure Ratio in the VVE Editor is based on the physical sensor, is it still ok to leave the MAF and Baro setup the way it is?
    Good question... that is where he was going with the logic of how it works. Just because the sensor is seeing boost in the charge pipe it may not matter if the barometer preset that the ECM uses isn't updated after key on engine off.

    I've got more digging to do, but this overall may be completely unnecessary if Baro doesn't update.
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  4. #44
    Senior Tuner DSteck's Avatar
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    I've watched GMVE show different values given the same MAP and RPM when baro is shown differently.

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  5. #45
    Advanced Tuner Redline MS's Avatar
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    Quote Originally Posted by LSxpwrdZ View Post
    He may be on to something though. HPT isn't scanning everything to do with Barometric Pressure, it's logging the physical sensor. However using a snap on scan tool there is another PID called Calculated Barometric Pressure and it is not updating with boost like the live reading is. Which makes me wonder if there really is anything wrong with just leaving the MAF and Baro setup the way it is...
    I think everyone is right in some part of this dissection. I'm willing to bet that somewhere in the cal is the ability to clip the max allowable range of calc baro reading as we can see from the calculated value vs the actual we see now. If so we could possibly close the window so baro never varies beyond say 102 Kpa....just speculating.

    With over 5000 tables in the stock ECU we have a lot we are missing.

    I'm still unclear on if the baro or calc baro is the one that is factored with Kpa to determine the load axis. If its the baro (which we know stops at 121) that's a huge swing. If its the calc baro which I found to limit at 108 (+/-) its still going to skew but with less error....but again which one is it...

    Dave's view of pulling it to keep it at true atmospheric makes sense but I think there is a table somewhere to resolve this.
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  6. #46
    Senior Tuner DSteck's Avatar
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    For now, pulling it erases any doubt that baro (be it calculated or actual) is wrong.

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  7. #47
    Advanced Tuner Redline MS's Avatar
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    Quote Originally Posted by DSteck View Post
    For now, pulling it erases any doubt that baro (be it calculated or actual) is wrong.
    Agreed. Good discussion though.........
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  8. #48
    Senior Tuner DSteck's Avatar
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    I'm honestly more curious about why LT4s are set the way they are. Surely the ECM uses the TIAP and SCIAP for the throttle calculations.

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  9. #49
    Advanced Tuner Redline MS's Avatar
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    You would think so since its needs it for supercharger diagnostics as well as inlet diags. We are in the midst of a LT4 build with a centrif blower trying to decide if we are going to set it up blow through or draw through. Much of this thread is weighing into this.
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  10. #50
    Senior Tuner Higgs Boson's Avatar
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    in the updated beta the LT4 is indeed SC-SCIAP-TIAP

    a 2015 6.2L Silverado is NA-TIAP (no map or baro)

    2014 M7 C7 is NA - MAP - TIAP


    I am wondering if I should change my broken out Baro/TIAP C7 to NA-MAP-Baro instead.....?

  11. #51
    Advanced Tuner Redline MS's Avatar
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    Quote Originally Posted by Higgs Boson View Post
    in the updated beta the LT4 is indeed SC-SCIAP-TIAP

    a 2015 6.2L Silverado is NA-TIAP (no map or baro)

    2014 M7 C7 is NA - MAP - TIAP


    I am wondering if I should change my broken out Baro/TIAP C7 to NA-MAP-Baro instead.....?
    We just built a C7Z and remove the factory supercharger. During this build we moved a few of the sensors around. The car was pissed off until we changed that Pressure Configuration to a LT1 setting.....it worked. This would indicate that the config setting is probably moving a bunch of things around inside the OS.....I'll know this week what else it messed up when we start to cal it....
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  12. #52
    Senior Tuner LSxpwrdZ's Avatar
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    Just a little update on this. Did another centrifugal setup couple weeks ago after finally getting my harness in to breakout the Baro and IAT sensor. The car performed a 1000x better with the sensors setup this way.

    Another note, I played around with it a bit and it seems that when there is no Baro sensor reading the ECM defaults to a MAP based barometer setting. I didn't get to play with this much due to time constraints but just looking up the delivered GMVE at a preset RPM and load gave me the same PRatio whether the Baro was connected and reporting correctly or not connected at all. However when the baro saw boost (in charge pipe) it did skew the PRatio. I found that interesting.
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  13. #53
    Senior Tuner Higgs Boson's Avatar
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    I have mine broken out with DStecks kit and it is working great. I also set my tune to NA - MAP - BARO without issue, not sure it's any different than leaving it TIAP, though.

  14. #54
    Higgs did u get the issue fixed on ur c7

  15. #55
    Senior Tuner Higgs Boson's Avatar
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    yes, the lash cap caused enough hpfp lift to push the pump off the block by shearing the mounting bolts.

    lash cap = bad

    new z06 pump is on, i am all tuned under 4500 or so RPMs and installing a secondary lift pump (from CPR in AZ) as we speak so I can finish up and see how much E85 the Z06 pump can support (also have Z06 rails and injectors).

  16. #56
    I hate to revive an old ass thread...but i have a 15 escalade that has the break out, it wont behave on na-map (stock setting is na-tiap) but baro still climbs a full psi during a pull. Actually I just realized the parameter "Barometric pressure" does, but "Barometric pressure sae" does not. great...which do i trust...

    I'm having some weird throttle hang and lazy throttle at low openings so I'm looking at anything i can find as out of the ordinary.

    Tony

  17. #57
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    I recently installed a baro breakout on my c7z. Under wot, it reads 5 points higher, 104.5 vs 99.5. Any ideas on a fix? match values of LS3

  18. #58
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    Quote Originally Posted by ayousef View Post
    This is from the E78 tuning guide.



    The baro sensor depicted in those images seem to suggest its a seperate sensor altogether, which doesnt make sense.
    I realize this is an older thread, but I want to add something. I have experience with the E78 as used on the GM 1.4 Turbo engines. The 2011 Cruze "DOES" have an external Baro sensor. The 2012 on up has the Baro sensor in the MAF that is located in the air filter "box." Is it possible the same thing applies to E78 use in the V8 vehicles.
    I'm still not sure just what the Baro sensor does with the tune. I know the VVE is laid out with baro/map pressure ratio rows and RPM columns.

    My 1.4 vehicle runs in SCCA autocross and is required to use a 33 mm restrictor in the turbo inlet air tube. I run the MAF after the restrictor and have noticed the baro reading will go lower at high airflow rates. I assume this is caused by a restriction of air flow by the restrictor, OR, a restrictive air filter.
    I am currently running in SD open loop mode.

    Suggestions would be greatly appreciated.

    Del Long


    2019-11-21
    I've done some further testing, by removing the air filter, running car down 300 foot driveway and the log shows the baro pressure still drops from 14.2 to 8.5. Remove the 33mm restrictor and the baro only drops to 14.1. So, it is the restrictor that causes the drop. I think this is normal, and that is what a turbo that is capable of flowing more CFM than the restrictor will allow will do. Now the question is, "Just what is this baro sensor reading used for"?


    Del Long
    Last edited by sprinto7; 11-21-2019 at 12:57 PM.

  19. #59
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    Quote Originally Posted by sprinto7 View Post
    I realize this is an older thread, but I want to add something. I have experience with the E78 as used on the GM 1.4 Turbo engines. The 2011 Cruze "DOES" have an external Baro sensor. The 2012 on up has the Baro sensor in the MAF that is located in the air filter "box." Is it possible the same thing applies to E78 use in the V8 vehicles.
    I'm still not sure just what the Baro sensor does with the tune. I know the VVE is laid out with baro/map pressure ratio rows and RPM columns.

    My 1.4 vehicle runs in SCCA autocross and is required to use a 33 mm restrictor in the turbo inlet air tube. I run the MAF after the restrictor and have noticed the baro reading will go lower at high airflow rates. I assume this is caused by a restriction of air flow by the restrictor, OR, a restrictive air filter.
    I am currently running in SD open loop mode.

    Suggestions would be greatly appreciated.

    Del Long


    2019-11-21
    I've done some further testing, by removing the air filter, running car down 300 foot driveway and the log shows the baro pressure still drops from 14.2 to 8.5. Remove the 33mm restrictor and the baro only drops to 14.1. So, it is the restrictor that causes the drop. I think this is normal, and that is what a turbo that is capable of flowing more CFM than the restrictor will allow will do. Now the question is, "Just what is this baro sensor reading used for"?


    Del Long
    More reading and testing. On the 2013-2019 GM 1.4 Turbo with the E78 ECM the baro is used to select the correct cell in the VVE table for fueling. I can see be my latest logs that as the boost and RPMs reach a certain level the BARO reading drops, the fueling changes, the power drops. I assume this is due to the change in Pressure Ratio. I'll log Pressure Ratio when I can get on the Dyno, or the snow melts off the driveway. Slicks and snow cover do NOT work together.

    *** The 2011 1.4 Turbo uses a 5 wire MAF, and a separate Baro sensor out in the open air. In the Sensor config section it has a separate Baro selection. Several tables are very different in that tune.
    Del Long
    Last edited by sprinto7; 01-20-2020 at 07:31 PM. Reason: More Inforamtion

  20. #60
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    Quote Originally Posted by DSteck View Post
    I guess I need to be more clear.

    On the LT1, the barometric pressure reading absolutely comes from the throttle inlet air pressure sensor, which is integrated into the mass air assembly. Log barometric pressure on a centrifugal setup that has the MAF after the blower and you'll see this value change once you go into boost.

    Now, cut the wiring and wire up a normal LS3 map sensor to those wires (LS3 map sensor uses the exact same core as the one inside the MAF) and hang it in free air in the engine bay. Repeat your test and you'll find that the baro reading now stays constant no matter what you do. This is depending on leaving the model set to NA-MAP-BARO.

    I've done this twice now because I was sick of the junk barometric pressure readings. There's no need to shut down the updating. You just need to set up a proper baro sensor that isn't on the outlet side of a compressor.

    Wire 4 on that diagram is where the baro signal comes from. I will invite anyone to verify this. I need money too, so if anyone wants to bet, I'm game for that too. Lol.
    Hopefully you are still an active user in the forums. I came to the HP Tuners forum looking for help with the exact set up that you have just described. I have the 8 wire MAF in a centri configuration. I used my OE 1 bar MAP sensor that i replaced with a 3 bar to support the blower pressure in the intake. So every time i give it some throttle my ambient pressure climbs from the typical 13.9 to 15.9 every time. And the logical solution was to do the breakout. However, Im not quite sure how to set the tune to support this. After just pluging it all in and turn the ign on the ambient pressure is way off. Im can think of a couple possibilities as to why and figured i would just ask instead of tearing into with a DMM. Is my issue that i would need to be adjusting the AAP1/2 offsets? would i be changing the the map sensor config from NA-MAP-TIAP to NA-MAP-BARO?
    i wasnt certain if the ambient temp shared the 5v ref and low ref with the pressure sensor circuit so i had just T-taped those 2 wires with a very good (better than most) soldered connection. My method does not break the original wire but the addition of the device could skew the resistance ever so slightly, but enough to cause issues if it is sensitive enough. I strip a section of the jacket and spread the wire strands into two pairs and insert the tape wire threw the middle the twist the wires together and solder. Without the solder, just the twisted pairs makes such a good mechanical connection, you cant pull them apart. then add solder and its as good as if it was meant to be.