Resolved GM 3 Bar problems

[Yamahaulin]

I'm having trouble with my brand new gm 3 bar. I can't get it to read 0 with the car off. I've seleced it in the pinouts as gm 3 bar. I would love to post the log so you guys could check it out but for some reason it won't let me upload a file, i've been having this trouble for weeks now. For those that can view ecmlink forums http://www.ecmtuning.com/forums/showthread.php?t=82712 log is posted.

 

[Mello]

You have a GM 3 Bar "MAP" sensor? MAP means "Manifold Absolute Pressure" and at sea level you would be at 1 atmosphere which is roughly 14.69psi. So, with your car off the manifold pressure would equal atmosphere pressure & would read ~14.7psi. You could only get to 0psi on your MAP out in space where there is no pressure. As you go higher up from sea level atm pressure drops. For me Im at 7000ft and my atm pressure is ~12.6psi; car off. Once you start your car when idleing you will have vacuum and the MAP will read lower than 14.7 psi. I idle at about 9-10psi. Psi & in-hg are different BTW, so don't mix units.

 

[Yamahaulin]

In the log it's reading in-hg. Is there a way to turn that into psi?

 

[jim95redgsx]

In the log it's reading in-hg. Is there a way to turn that into psi?

You have to add "GM3bar" to your Captured Values. You must be connected to the car to do this.
The way you are logging it now, as MDP, it thinks you are logging a stock MDP sensor, which uses a completely different calculation routine.
It will read in/hg during vacuum and psi during boost.
Jim

 

[Fullthrottle7]

You have a GM 3 Bar "MAP" sensor? MAP means "Manifold Absolute Pressure" and at sea level you would be at 1 atmosphere which is roughly 14.69psi. So, with your car off the manifold pressure would equal atmosphere pressure & would read ~14.7psi. You could only get to 0psi on your MAP out in space where there is no pressure. As you go higher up from sea level atm pressure drops. For me Im at 7000ft and my atm pressure is ~12.6psi; car off. Once you start your car when idleing you will have vacuum and the MAP will read lower than 14.7 psi. I idle at about 9-10psi. Psi & in-hg are different BTW, so don't mix units.

I like many of your posts but this is a bit off. A MAP sensor is exactly what you mention, an absolute sensor it doesn't account for atmosphere but the mistake that you made is the scale that it operates on. The first bar is for reading vacuum which is how all of the MAP sensors used can show when an engine is in vacuum usually down to 30in/hg. You can roughly convert inch/mercury to psi with calculators online if you actually want to see it in a negative PSI but that isn't going to help with any tuning since everyone is used to the std nomenclature. If you tell them you're at negative 14 psi they'll think you mean 14in/hg which is only about half the equivalent merc reading which in that case would be closer to the 30in/hg lower limit...

Space has a vacuum in a similar way that an engine at idle is in vacuum so I'm not sure why you'd think that if you went into space it would be zero? A properly calibrated MAP (they are almost all self calibrating, btw) should definitely read zero with the engine off unless you have messed with your settings and set it up as a linear sensor and redefined the lower voltage limit to be at zero instead of in vacuum and the upper limit at an actual positive 3 bar. This is why a 3bar sensor is only good for about 30psi, if it could measure 3 bar from zero you would be able to get away with using one above 40psi which is not the case. Altitude definitely does affect the atmospheric pressure that you experience, but again a MAP sensor doesn't care because its an absolute sensor. You simply need to adjust the setting in DSMLink within that sensor's preferences to reflect the altitude that you are at and it will then read zero with the motor off. If its still a few tenths off then adjust the altitude farther until it reads zero. Presto!

 

[Yamahaulin]

You have to add "GM3bar" to your Captured Values. You must be connected to the car to do this.
The way you are logging it now, as MDP, it thinks you are logging a stock MDP sensor, which uses a completely different calculation routine.
It will read in/hg during vacuum and psi during boost.
Jim

Did this and problem solved now it reads correct. Thank you for the help.