Hello community,
My MAP readings are off and im just here for brainstorming. My external defi gage reads about -15psig. In absolute terms this should be hovering around 0 if im not mistaken. My log shows a constant 15.23ish psia. I have confirmed i have 5 volts at the sensor, swapped sensors for a new one and have my MAP ouput pinned to B37. See below. Any thoughts? I’m a 42 year old newb doing this for fun so if you want to rag on me for being a newb before offering feedback I’m game. Thanks.
MAP (manifold Absolute pressure) is an absolute measurement, where MGP (manifold Gauge pressure) would be referenced to atmosphere.
The ECU wants an absolute value for the MAP sensor input, you have nothing really wrong here.
(to get really deep, 15.23 PSIA puts you at 1000 feet below sea level so there’s probably a slight calibration issue there)
in PSIG 0psi would be atmosphere, in PSIA atmosphere is x pressure above a perfect vacuum.
You can use the built in MAP sensor as a barometric sensor, which would be measuring atmospheric pressure in PSIA.
Hi,
This is the best visual representation of pressure measurements I found recently:
You can read more about pressure sensor types here:
https://www.linquip.com/blog/pressure-transducer-types-and-definitions/
To understand pressure sensors better, it’s essential to recognize that every pressure sensor that exists is a differential pressure sensor. That means they always measure a difference in pressure between two points in space.
An absolute pressure sensor is a differential sensor that has a permanently connected reference vacuum chamber on one side. This sensor measures any pressure in relation to a “perfect” vacuum.
Gauge pressure sensors measure the pressure in relation to the ambient pressure. Now, there can be two types. The sensor can have a reference chamber with a standard pressure (100 kPa) or standard ambient pressure (101.3 kPa). Alternatively, they can measure in relation to the actual ambient pressure present around the sensor. In that case, one part of the differential sensor is open to the atmosphere.
That doesn’t make a lot of sense. A gauge pressure of -15 PSIg indicates a perfect vacuum at an altitude of 500 m (1640 ft) below sea level. That is lower than any dry land on Earth. Either you made a mistake or the gauge is faulty.
What sensor are you using?
How is your calibration table looking?
Tthank you!
My defi gauge has always measured vacuum when idling and increasing pressure as i throttle up and boost builds, even while on factory ecu. Its just your typical, in-dash (or A pillar) gauge that sits in a pod. Stupid or not I had never looked at it in detail and it reads [in. Hg]. So the reading is more like -7 psi while its idling. Its this:
Meanwhile, my vvti 2jzgte MAP sensor (see above) is reading a constant 15.23 psia and the car runs like ass. Both sensors are connected side by side to the intake manifold so I expect consistent readings after applying conversions. I just took the plugs out and verified that timing was good and it is. The plugs themselves look rich. I’m a tad frustrated but also old, so patient hehe. Thanks for taking the time guys.
-7 psi sounds plausible for idle.
Whats the voltage of the 2JZ gte map sensor doing? kind of sounds like it’s in error or pinned out wrong.
Post a tune file and a log, that will help us help you. couple questions not yet answered that may be the culprit.
Yep, that makes a lot more sense.
We need to check your calibration table.
Please post the project file or a picture of the table.
