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View Full Version : Map sensor question / 37 psi @ sea level?



Boost
October 29th, 2013, 06:58 PM
I've been wondering about this for a while but have not had the chance to check the part #s on the sensors yet. I am assuming that all 3 vehicles I am working on have a GM 3 bar map sensor as the all run more than 15 psi boost from the factory (although they could possibly use a 2 bar "boost sensor" just for pressure?)

Perhaps I am logging / looking at the wrong PID - or doing something even more foolish. The E39A, E78, and E35B all seem to max out at 37.0 psi "Intake Manifold Absolute Pressure". I have been looking at this PID and subtracting about 14.6 to estimate boost pressure because I am at sea level.

I find it hard to believe that all 3 vehicles are topping out at around 22 psi, regardless of the tune I am running. At first I really thought the map sensor was maxing out, but then I realized if they were using a 2 bar it would max out at less than factory boost?

It is also possible that I am not understanding something about basic map sensor operation...

darcy
October 29th, 2013, 07:19 PM
Aren't the factory boost systems 2.5bar? (2.5 x 14.6 = 36.5)

GMPX
October 29th, 2013, 08:03 PM
What is 22psi in kPa? If it is 255 then that is the upper limit of the ECM.

kangsta
October 29th, 2013, 08:08 PM
37psi is the limit of the ECM. 255kPa = 36.98 psi

GMPX
October 29th, 2013, 09:10 PM
Sorry, I meant to say 37.0 psi (as Roland posted), not 22.

Boost
October 30th, 2013, 02:04 AM
Aren't the factory boost systems 2.5bar? (2.5 x 14.6 = 36.5)

If that was the case it would suggest that at sea level I am running 2.5 bar boost (?)
I feel extra dumb today but the only way to learn this correctly is to ask questions and understand the answers. Let me look this up in GM Service information to see if there is a Descripton and Operation...

Boost
October 30th, 2013, 02:14 AM
Let me look this up in GM Service information to see if there is a Descripton and Operation...

Ok so on the LHU engine (E39A) there is a "Intake Air Pressure and Temperature Sensor" that I suppose only has to read boost and a MAP sensor that may only need to read vacuum to low boost (?)

16040

#16 is the "boost sensor" & #18 is the map sensor