What happens when using wrong MAP offset values?

[DRTWRK]

I recently upgraded my turbo and found I also needed to adjust/increase my VE table values in the upper kpa cells. Well! In reviewing my tune I come across the MAP Sensor calibration and started to question the values.
I have been tuning a 2 bar OS for a while and using a GM#12580698 map sensor which I set the linear setting to 200 & offset value to 10.33 in the calibration settings. Don’t remember where I got these numbers.
So back to the search feature I go!!!
After substantial hunting and reading I found reports that the offset value should have been (8).
Today I changed the offset value to (8) and found my WB02 reflecting leaner A/F ratios at corresponding kpa values . I run up to approx. 150-160-kpa only. I did not push it further to the 206-208 kpa normal boost level.
Can someone please explain what function the offset table performs and how it affects the tune?
Further, can someone please verify the linear and offset values for the GM#12580698 sensor?
Will I be doing my tune an injustice by leaving the previous value as long as I acquire the proper A/F ratio and the WB02 and Commanded agree?

[DRTWRK]

Anybody???

[5_Liter_Eater]

You want it to be correct. The MAP output is linearly correlated to manifold pressure so the offset tells it what kPa 0V equates to and the linear tells it the slope.

Here is a thread on it: http://www.hptuners.com/forum/showthread.php?t=11480

Use 200 for the linear and 8 for the offset and then edit the offset up or down until it reads 105 kPa with the engine off.

[DRTWRK]

You want it to be correct. The MAP output is linearly correlated to manifold pressure so the offset tells it what kPa 0V equates to and the linear tells it the slope.

Here is a thread on it: http://www.hptuners.com/forum/showthread.php?t=11480

Use 200 for the linear and 8 for the offset and then edit the offset up or down until it reads 105 kPa with the engine off.

Thanks, That is the thread I found in a search that got me to questioning my previous offset values of (10.33)
Yesterday, I had another person from LS1 Tech inform me that this 10.33 value was indeed the correct offset for that sensor. Not to question eithers knowledge but I'm at a loss on what to do. When I turn my ignition on with engine not running all I get on my MAP reading is zero. What am I doing wrong? Your time is appreciated.

[5_Liter_Eater]

What units are you logging MAP in? Also I thought you had to delete the regular MAP PID and add the "three bar MAP" PID on the 3rd gens.

[TURBO 6.0]

You want it to be correct. The MAP output is linearly correlated to manifold pressure so the offset tells it what kPa 0V equates to and the linear tells it the slope.

Here is a thread on it: http://www.hptuners.com/forum/showthread.php?t=11480

Use 200 for the linear and 8 for the offset and then edit the offset up or down until it reads 105 kPa with the engine off.

Shouldn't the MAP only read 105 if you are at sea level? I am in Utah and the BARO pressure is 85.6 KPA. Is that the number I should be shooting for with the engine off?

[Frost]

Shouldn't the MAP only read 105 if you are at sea level? I am in Utah and the BARO pressure is 85.6 KPA. Is that the number I should be shooting for with the engine off?

You are correct.

He made this thread on tech, and here is one way I would do it: http://www.ls1tech.com/forums/12318735-post7.html

[5_Liter_Eater]

Yea, sorry I made the presumption that he was at sea level. Regardless, it shouldn't be zero.

[Frost]

Yea, sorry I made the presumption that he was at sea level. Regardless, it shouldn't be zero.

I tuned a turbo swap a week ago that at first had a failed MAP (have had many of the newer GM 2bar MAP that is a replacement for the unit ending in 698 fail) and after looking closely at it's replacement, I noticed some odd behavior. At key-on it reads 0, if you crank for a split second but it doesn't start, it will read 102-103 as it should, but at first key-on it always read 0. Weird. Again, this is a 2bar OS.

[TURBO 6.0]

I am using a 12615136 sensor from GM. I have heard that it is actually closer to a 2.5 bar MAP. Is this true? It seems to be correctly reading with just the ignition on at 85-86 KPA (Utah) but at 8.5-9 psi boost it's only going to 125-130 KPA. It seems like it should be closer to 145-150 kpa right?

[Frost]

The unit ending in 136 is the sensor I was talking about failing actually... I have seen no less than a half dozen of that part number fail this year.

I also haven't had any problems with how it reads. Do you have the linear value setup properly?

[TURBO 6.0]

The unit ending in 136 is the sensor I was talking about failing actually... I have seen no less than a half dozen of that part number fail this year.

I also haven't had any problems with how it reads. Do you have the linear value setup properly?

To be honest I'm not sure weather it's setup properly or not. What numbers should I have in for the offset and the linear? Right now I have 200 for the linear and 9.49 for the offset.

[DRTWRK]

You are correct.

He made this thread on tech, and here is one way I would do it: http://www.ls1tech.com/forums/12318735-post7.html

Is there not a specific value given by the manufacturer?

I have been advised so far of the (200 & 10.33 offset value) and (200 for the linear and 8 offset) and turning key on while logging without engine running and somehow adjust to obtain 105 kpa.

Also, your suggestion on how to obtain correct value seems ok if I had the time was not so lazy.
I do appreciate all here that offered because I surely don’t know.

Is it possible we could obtain some mutual agreement or will these different recommendations all achieve the same goal somehow?

[Frost]

I don't recall the linear off of the top of my head (no tuning files on this computer) but it should be available in a data sheet if it's in question.

105 is not necessarily what you are looking for. Look at my link in post 7 for an easy way to figure out where you need to start.

[TURBO 6.0]

What are the correct PID's / sensors that I should be logging in the scanner? Right now I am logging manifold air pressure 2bar which seems to be reading somewhat accurately at around 150kpa at full boost. The primary VE table in the histogram will only go to 130 kpa though?