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Thread: Barometer Update Parameters

  1. #1
    Senior Tuner LSxpwrdZ's Avatar
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    Barometer Update Parameters

    Working on a 15 C7 with an A&A Kit and noticed on a pull that my Baro reading would climb. I'm assuming these get the baro reading from the MAP sensor like in the past. With the baro being off the PRatio readings are going to be wrong as well. Anyone else ran into this issue?
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  2. #2
    Senior Tuner Ben Charles's Avatar
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    James I'll scan my car tomorrow and look at the Baro sensor on my 15. I was tuning my GMVE tables the other day and didn't notice anything unusual though

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    it does this on my whipple truck as well, despite the fact that my MAF sensor sees no boost pressure at all so im guessing its located in the MAP sensor and I hope its one of those things that could be independently relocated.
    Last edited by ayousef; 07-15-2015 at 09:22 PM.

  4. #4
    Senior Tuner DSteck's Avatar
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    There is a map sensor built into the MAF. It live updates and provides the ECM with a baro reading.

    This is why I break it out.

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  5. #5
    I ran into this today as well. So you're saying that the Baro sensor is part of the maf? What do you mean you break it out? My Baro reads builds to 121 kpa like that is the limit it can register.

  6. #6
    Senior Tuner Ben Charles's Avatar
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    it does this on my whipple truck as well, despite the fact that my MAF sensor sees no boost pressure at all so im guessing its located in the MAP sensor and I hope its one of those things that could be independently relocated.
    This is my opinion, but the LS9 used a Separate Baro sensor and an actual 3 bar Map sensor. From what I can tell the LT4 C7 Z06 just uses "NA-MAP-Baro" sensor where the LT1 uses a "NA-MAP-TIAP" sensor. IF running a PD blower like you I would try to use the LT4 Map and set it up in the tune for it. Possibly the code bypass what it sees at the MAF sensor baro reading and goes off the actual LT4 map senor?? ($25 from GM)

    Tick, if you seeing 121 I'm sure that's just an error on the reported reading, no reason for that to change. But like James mentioned that will throw off the (Map/Baro) pressure ratio.

    I'm not able to look at you file (my beta ran out a couple of days ago and waiting for Bill to flash it back on my page) but you need to alter DD tables in the entire throttle percent, not just 100% rolls, that will make a big change. Also have you noticed it shifts very sluggish in SD mode? The Tq coefficient tables need to be increased, this will help quite a bit.

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    Quote Originally Posted by Ben Charles View Post
    This is my opinion, but the LS9 used a Separate Baro sensor and an actual 3 bar Map sensor. From what I can tell the LT4 C7 Z06 just uses "NA-MAP-Baro" sensor where the LT1 uses a "NA-MAP-TIAP" sensor. IF running a PD blower like you I would try to use the LT4 Map and set it up in the tune for it. Possibly the code bypass what it sees at the MAF sensor baro reading and goes off the actual LT4 map senor?? ($25 from GM)

    Tick, if you seeing 121 I'm sure that's just an error on the reported reading, no reason for that to change. But like James mentioned that will throw off the (Map/Baro) pressure ratio.

    I'm not able to look at you file (my beta ran out a couple of days ago and waiting for Bill to flash it back on my page) but you need to alter DD tables in the entire throttle percent, not just 100% rolls, that will make a big change. Also have you noticed it shifts very sluggish in SD mode? The Tq coefficient tables need to be increased, this will help quite a bit.
    forgot to mention that I also have an LS9 3bar map sensor on my L83 truck, so it must be that the baro sensor is in the MAF as DSteck suggested, however with the PD blower my MAF sensor sees zero psi of boost, yet it seems that the huge volume or air moving at a very high speed could mess up the readings.

    Edit: Okay I just opened a recent log and noticed in my logs the baro readings actually drop from 99kPa to about 93-94 at higher revs. this seems to match my theory above, high speed air = lower pressure, Bernoulli's principle of fluid dynamics in action? I dont know.

    So it would seem that centrifual and turbo guys that want to tune in SD should relocate the baro sensor from the MAF.
    Last edited by ayousef; 07-15-2015 at 11:06 PM.

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    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.

  9. #9
    Senior Tuner DSteck's Avatar
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    It's in the MAF. The new MAF doesn't have eight wires just for fun.

    The C7Z uses NA-MAP if memory serves me right.

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  10. #10
    Quote Originally Posted by Ben Charles View Post
    This is my opinion, but the LS9 used a Separate Baro sensor and an actual 3 bar Map sensor. From what I can tell the LT4 C7 Z06 just uses "NA-MAP-Baro" sensor where the LT1 uses a "NA-MAP-TIAP" sensor. IF running a PD blower like you I would try to use the LT4 Map and set it up in the tune for it. Possibly the code bypass what it sees at the MAF sensor baro reading and goes off the actual LT4 map senor?? ($25 from GM)

    Tick, if you seeing 121 I'm sure that's just an error on the reported reading, no reason for that to change. But like James mentioned that will throw off the (Map/Baro) pressure ratio.

    I'm not able to look at you file (my beta ran out a couple of days ago and waiting for Bill to flash it back on my page) but you need to alter DD tables in the entire throttle percent, not just 100% rolls, that will make a big change. Also have you noticed it shifts very sluggish in SD mode? The Tq coefficient tables need to be increased, this will help quite a bit.
    I haven't really noticed that the shifts are sluggish in SD mode, but I haven't driven it a whole lot on the street and for the dyno I've got weird shift tables to make it stay in 4th gear. What torque coefficient tables specifically are you saying needs to be increased, and by how much? Now that I'm in SD the 'Engine Torque' parrameter is reading way higher than what it did at the same power level before with the maf on. Like 1,100 ft. lbs now compared to 800 with the maf on. I can't make it go to the full 84% throttle now but it would before. I've maxxed out the maximum torque table and at first that fixed my timing retard issue during the pull, but then I increased the DD table in the bottom rows again (1500 in the 100% tps row) and the timing retard came back.

  11. #11
    Advanced Tuner Road's Avatar
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    The baro reading comes from the Map sensor not the Maf sensor. The LT4 uses a different Map setup from the LT1 to keep baro from climbing under boost. Ben Charles theory should resolve the baro increase issue.
    Attached Images Attached Images

  12. #12
    Senior Tuner DSteck's Avatar
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    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.

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  13. #13
    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.
    I unplugged my MAF while logging with the engine off and baro fell from 97 kpa to 0 so obviously baro is being read by the sensor in the MAF.

  14. #14
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by Tick View Post
    I unplugged my MAF while logging with the engine off and baro fell from 97 kpa to 0 so obviously baro is being read by the sensor in the MAF.
    Ding!

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  15. #15
    Senior Tuner LSxpwrdZ's Avatar
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    Makes perfect sense because loaded on the dyno at part throttle the charge pipe was in boost but the intake was not due to low throttle angles but it would make my baro readings jump up to 121ish. Guess there is a use for the original map sensor from the LT1's after replacing it with the ZR1 3bar... Gonna have to order some pigtails to keep in stock for those things. I really don't understand why these "Kits" don't come with the necessary sensors to properly calibrate the ECM's with their kits. Every one of these blower kits should include a ZR1 MAP sensor as well as a break out harness for the baro reading from the MAF wiring.
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  16. #16
    Senior Tuner DSteck's Avatar
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    Pretty soon, I will be selling harnesses that do everything needed to make these work properly. MAP and IAT breakout with sensors as well as a connection for an Alky Control MAF to voltage converter. It'll all be PnP.

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  17. #17
    Advanced Tuner Road's Avatar
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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.
    Here is your verification straight out of SI. .
    Attached Images Attached Images

  18. #18
    Senior Tuner LSxpwrdZ's Avatar
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    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.
    James Short - James@ShorTuning.com
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  19. #19
    Advanced Tuner Road's Avatar
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    Quote Originally Posted by LSxpwrdZ View Post
    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.
    Why would you be reading boost at the maf sensor?

  20. #20
    Quote Originally Posted by Road View Post
    Why would you be reading boost at the maf sensor?
    Centrifugal blower or turbo..... I've got logs and a screen shot posted in my thread on here showing it happen. And I disconnected the MAF today and baro went to zero. I've already 'broke' it out as Dsteck mentioned using the stock MAP i removed from the intake when the zr1 map went in and a GM pig tail we had on the shelf. Baro holds at 97 during the pull now instead of going up to 121.