weird Map sensor issue

[BLeeBull]

I looked everywhere for an answer but I really can't find one. In the middle of doing a SD tune on my truck I noticed something. I have a 12589161 VCM. Key on engine off my map sensor reads 4 volts when my current local pressure is 101.7kpa. This has my barometric pressure showing on the scanner as 81.4kpa. This is with a new AC Delco 12644228 map sensor. I replaced it thinking it was bad, but the old and new sensor reads the same. I scaled the MAP in my tune by taking the voltage with the key on engine off and dividing that by the current outside pressure 4.01v/101.7kpa and then multiplying that number by 4.90 (my tested reference voltage) and ( That left me with an assumed value of 123.41kpa at 4.9) volts. So I entered 126.8kpa 5 volt value in the map sensor linear box and around 4kpa in the offset to get the scanner and the mighty vac to read about the same. Now with KOEO the scanner shows correct baro. This can't be right so something must be wrong. What is the correct way to deal with this? Maybe none of it really matters. It had it fueling properly before I ever noticed the MAP error and after I made the change I had to work on the VE table to get it back right.

[blindsquirrel]

Your posts are going to keep getting zero replies if you keep not posting tune/log files for specific questions like this over and over.

Post the tune file.

Post a log file.

Tell us what you are working on and what has been done to it. Is it a swap? All original? Year? Give us something other than a walloftext story about this thing that happened that one time when you were at that place where they do the stuff.

-----

The platforms that use 12644228 have a complicating factor in that they also (at least some of them do, I don't have infinite time to look up every vehicle) have a separate BARO sensor that looks exactly like the MAP sensor, but the two sensors are electrically different and use different linear/offset settings. Do you know for a fact that 12644228 is the MAP and not the BARO? They will fit in the same mounting locations.

[BLeeBull]

Your posts are going to keep getting zero replies if you keep not posting tune/log files for specific questions like this over and over.

Post the tune file.

Post a log file.

Tell us what you are working on and what has been done to it. Is it a swap? All original? Year? Give us something other than a walloftext story about this thing that happened that one time when you were at that place where they do the stuff.

-----

The platforms that use 12644228 have a complicating factor in that they also (at least some of them do, I don't have infinite time to look up every vehicle) have a separate BARO sensor that looks exactly like the MAP sensor, but the two sensors are electrically different and use different linear/offset settings. Do you know for a fact that 12644228 is the MAP and not the BARO? They will fit in the same mounting locations.

Engine is a 2004 LQ9 out of an escalade installed in an older (1995) truck. 12644228 is the MAP. System does not have a seperate baro sensor. Baro seems to update when the key is turned on. If I remove the map from the intake and hook the hose from my vac pump to the nipple on the map, and pull vac on the sensor, the map readings on the scanner change. (eg, if i pull 15" of vac on the sensor, the map readings show about 50kpa.) and If I pull vac on the map with the key off and then turn the key on, the baro reading on the scanner will be offset by the amount of vac i i have applied to the sensor. I already established what I have. When my tune has the standard 1 bar offset of 10.34 and a linear of 94.43 entered, the scanner shows baro at around 82kpa when actual baro is about 101kpa. Other than what I did, what is the proper way to scale the sensor? Are you telling me the 12644228 is not a map sensor? The original map sensor with the same number as the new one was in the TBSS intake when I pulled it off of a TBSS in the junkyard. Attached is the tune file that was in the VCM when I noticed the baro reading about 20% less that actual.

new questions:
1) does anyone know if AC delco part number 12644228 is a 1 bar map sensor?
2) is it normal for the 12644228 sensor to read about 20% below actual?
3) what is the correct linear and offsets for a 12644228 sensor if it is not a standard 1 bar sensor?
4) what in a tune would cause a sensor to show low voltage? Would a bad computer cause this?

[eXo3901]

Quick search turns up 12644228 being used on the 4.6l Trailblazer. I do not see it showing up for the TBSS. Luckily, the tune repository has a stock file for a 2008 4.6L trailblazer! Contained within said calibration is a linear value of 128.20kpa and a offset value of -0.30kpa. There are barometric sensor inputs as well but they are both 0kpa. Lastly, the repository file has a MAP estimate max value of 105kpa and estimate min value of 10kpa.

[BLeeBull]

Thank you. I guess my new scaling was close.

[BLeeBull]

Quick search turns up 12644228 being used on the 4.6l Trailblazer. I do not see it showing up for the TBSS. Luckily, the tune repository has a stock file for a 2008 4.6L trailblazer! Contained within said calibration is a linear value of 128.20kpa and a offset value of -0.30kpa. There are barometric sensor inputs as well but they are both 0kpa. Lastly, the repository file has a MAP estimate max value of 105kpa and estimate min value of 10kpa.

Thank you again. I looked everywhere for info on that sensor and came up short. So i scaled it like I would industrial sensors like I do in my day job. I ended up at 126.8 and .4. All the information I could find on 1 bar crap was the typical 105/10 kpa so I figured something was up. I even looked for info on 1.25 bar sensors after figuring that was what I have with no luck. Totally amazing you were able to give info on the sensor part number I gave without needing a tune file like the other guy. I guess I am done now with my walloftext as that other guy said.

[BLeeBull]

There was nothing in my question that would require any more info than what I originally gave. I ask how to scale a MAP and you want useless info instead because you had no idea what the answer is. Instead of telling me that, I get your wallotext crap. Question: what in my tune or log file would have given you the information you needed to answer my question? Answer: nothing. Did you want the log file to verify the sensor really reads 4 volts at baro pressure, or are you just an a hole? After being an engineer for the last 30 years some things never change with guys like you, when they don't know the answer, they blame the question. Thanks for nothing. BTW, I am glan you didn't waste an infinite amount of time on this.

[BLeeBull]

Your posts are going to keep getting zero replies if you keep not posting tune/log files for specific questions like this over and over.

Post the tune file.

Post a log file.

Tell us what you are working on and what has been done to it. Is it a swap? All original? Year? Give us something other than a walloftext story about this thing that happened that one time when you were at that place where they do the stuff.

-----

The platforms that use 12644228 have a complicating factor in that they also (at least some of them do, I don't have infinite time to look up every vehicle) have a separate BARO sensor that looks exactly like the MAP sensor, but the two sensors are electrically different and use different linear/offset settings. Do you know for a fact that 12644228 is the MAP and not the BARO? They will fit in the same mounting locations.

There was nothing in my question that would require any more info than what I originally gave. I ask how to scale a MAP and you want useless info instead because you had no idea what the answer is. Instead of telling me that, I get your wallotext crap. Question: what in my tune or log file would have given you the information you needed to answer my question? Answer: nothing. Did you want the log file to verify the sensor really reads 4 volts at baro pressure, or are you just an a hole? After being an engineer for the last 30 years some things never change with guys like you, when they don't know the answer, they blame the question. Thanks for nothing. BTW, I am glad you didn't waste an infinite amount of time on this.

[blindsquirrel]

MAP sensor linear/offset are not adjustable as a tuning aid. A particular MAP part number has a specific, correct linear and offset for the readings to come out correct.

I know you are using that 12644228 as your MAP sensor. And I know that Gen 3's don't use a separate BARO sensor. What I was asking is, is that part number in the original Gen 4 application used as the MAP, or as the BARO? Because they look the same, use the same connector and pinout, but have different pressure vs voltage scales.

If 12644228 is the MAP from one of the applications that used it stock, say 2010 Silverado 1500 4.8L, then the correct linear/offset should be found in one of those files, which in that case would be 128.20/-0.30.

edit: speeling

[blindsquirrel]

I had to go looking through your post history to try to find some info on what you are working with and only found other threads more or less just like this one, with no year/make/model and no files, and no replies. I have to imagine that not getting replies can get frustrating, and now you know why that kept happening and what to do in the future to help us help you. You're welcome, Mr. Senior Engineer Person.

[eXo3901]

Thank you again. I looked everywhere for info on that sensor and came up short. So i scaled it like I would industrial sensors like I do in my day job. I ended up at 126.8 and .4. All the information I could find on 1 bar crap was the typical 105/10 kpa so I figured something was up. I even looked for info on 1.25 bar sensors after figuring that was what I have with no luck. Totally amazing you were able to give info on the sensor part number I gave without needing a tune file like the other guy. I guess I am done now with my walloftext as that other guy said.

I never claimed my answer to be correct. I just posted quick information I thought to be relevant. That said, the only way I found what I did was because you posted this:

intro....etc.. This is with a new AC Delco 12644228 map sensor. ...map sensor issue etc..

...blindsquirrel noted this:

The platforms that use 12644228 have a complicating factor in that they also (at least some of them do, I don't have infinite time to look up every vehicle) have a separate BARO sensor that looks exactly like the MAP sensor, but the two sensors are electrically different and use different linear/offset settings. Do you know for a fact that 12644228 is the MAP and not the BARO? They will fit in the same mounting locations.

...which prompted you to post this:

The original map sensor with the same number as the new one was in the TBSS intake when I pulled it off of a TBSS in the junkyard.

I then googled the part number followed by "trailblazer". Found a random result that listed potential applications the part number may be used on. Then went to rockauto to see if the part number showed up in their system and found it shows up for a 2008 4.6L trailblazer. I then got lucky that there was a 4.6L file in the repository that had the baro sensor inputs at 0kpa and linear at 128kpa. Which was close to what you calculated. So, assuming the repository file was legitimate, having 0kpa in the baro inputs all but confirmed what blindsquirrel pointed out. Which is, and I am assuming, that this part number is a MAP sensor and is used only as a MAP sensor in this specific OE application. So I did need more information than what was originally provided.

[dhoagland]

I never claimed my answer to be correct. I just posted quick information I thought to be relevant. That said, the only way I found what I did was because you posted this:



...blindsquirrel noted this:



...which prompted you to post this:



I then googled the part number followed by "trailblazer". Found a random result that listed potential applications the part number may be used on. Then went to rockauto to see if the part number showed up in their system and found it shows up for a 2008 4.6L trailblazer. I then got lucky that there was a 4.6L file in the repository that had the baro sensor inputs at 0kpa and linear at 128kpa. Which was close to what you calculated. So, assuming the repository file was legitimate, having 0kpa in the baro inputs all but confirmed what blindsquirrel pointed out. Which is, and I am assuming, that this part number is a MAP sensor and is used only as a MAP sensor in this specific OE application. So I did need more information than what was originally provided.

Nice response.

[BLeeBull]

I had to go looking through your post history to try to find some info on what you are working with and only found other threads more or less just like this one, with no year/make/model and no files, and no replies. I have to imagine that not getting replies can get frustrating, and now you know why that kept happening and what to do in the future to help us help you. You're welcome, Mr. Senior Engineer Person.

Senior? Thanks for throwing my age in there buddy. So I asked the question wrong. Again, what in any tune files or knowing what I am working on would have helped you answer my question? Here are my questions reformatted...I have a map sensor that puts out 4 volts at atmospheric pressure as shown by the scan tool and verified by DVOM. I have AC Delco bla bla sensor. Is the AC Delco Bla Bla Bla sensor different than a regular MAP sensor? Here is the method i used to scale it. Is this the proper procedure to scale it? Here is what I did and what I came up with, does this sound correct?

I looked up my baro at my current location
I divided that by the voltage shown on the scan tool
I then multiplied that by 5
I entered that value
into my 5 volt scale
I then pulled full vac on the map and messed with my offset to get it to read the same as my vacuum pump at the same voltage.
What is the proper way to do this?







.

[BLeeBull]

So my guess is that the sensor I am using has a little less resolution on a NA application than a true 1 bar sensor. So unless I plan on driving about 6500 feet below sea level I really don't need it. But I am waiting on the super tunnel from Ney York to London. Anyone know what the purpose of a sensor tha t is basically 1.25 bar sensor?

[blindsquirrel]

GM used that sensor on basically everything for over a decade. I guess not knowing why they did that makes me a dumbass and I learned nothing from 20 years in GM dealerships.

Another thing you can ask GM about is the Cobalt SS, since they used a separate BARO sensor on those that reads to 200kPa. A BARO sensor. It just sits there and measures atmosphere, with a max plausible range of, what, 30kPa total?

If you neglect to provide a year/make/model, usually we can just open your file and look at the details page. Clumsy, and kinda unnecessary to go through all that but it would at least be possible to find out. Instead, you're arguing about why you should have to tell anyone what combo of parts you needed help with. Seems counterproductive, but then it's been determined that I'm just a dumbass who knows nothing, not like someone with an engineering background.

[BLeeBull]

GM used that sensor on basically everything for over a decade. I guess not knowing why they did that makes me a dumbass and I learned nothing from 20 years in GM dealerships.

Another thing you can ask GM about is the Cobalt SS, since they used a separate BARO sensor on those that reads to 200kPa. A BARO sensor. It just sits there and measures atmosphere, with a max plausible range of, what, 30kPa total?

If you neglect to provide a year/make/model, usually we can just open your file and look at the details page. Clumsy, and kinda unnecessary to go through all that but it would at least be possible to find out. Instead, you're arguing about why you should have to tell anyone what combo of parts you needed help with. Seems counterproductive, but then it's been determined that I'm just a dumbass who knows nothing, not like someone with an engineering background.

i never clamed that you are a dumbass. My comment about engineers was a slam/dig on engineers (including myself I guess). I was pointing out that you answered a question much like engineers answer questions by shooting holes in the question. My engineering background is actually in electronics. Like old way back in the day old school shit like CRT TV sets, VCR's and CB radios because it was the 80's. for a few years I worked at a plant nursery testing soil samples and driving a dump truck while I was in school. Been a wrench most of my life and a stupid ASE master tech back when it meant something not like the Dino I am now. I got into working on cars because of my electronics background back in the 80's when the carb died. I understood how they worked because I was a TV repairman at the time and had oscilloscopes, and meters and shit to test the systems on cars the old school guys didn't know anything about. I guess I am somewhat behind the times now. Built engines of one type or another for a living or side gig most of my adult life, everything from Ski boats tractor pulls, to racing karts. Currently own a business with my son building kart racing engines. At about 40 I decided to go work for a company designing factory automation equipment. Fourteen years later it is still my day job. I like the kart engine stuff the best. We have an electronic flow bench, computerized dyno, accurate weather station, wideband O2, data logging, 3d valve seat cutting equipment, machine and honing equipment and more just to build kart engines. I can even program an industrial PLC if you give me enough weeks to do it in. So I am like a regular guy that's been involved is a bunch of crap. I am still figuring this car tuning crap out. So....that's enough about me.