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I'm working on a boost gauge for my R53. It features a red needle that sweeps from vacuum to 20psi boost. A yellow tell tale needle follows and holds at the highest boost reached and slowly decays after 1minute. The intake air temperature is also shown.
Right now it's in simulation mode, but plan is to tap into the signal from the boost sensor on the manifold to pickup the boost and air temperature and process it.
I like it is a great project! I'm excited to see progress!
Spoiler
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Last edited by LaurenCollins; Feb 21, 2025 at 10:40 PM.
I've fished a 4 wire cable from the TMAP sensor on the intake, into the cabin and into the gauge pod. There was a spot on the driver side that goes through the firewall near the brake reservoir. Some pics below.
I've searched for the datasheet of the TMAP sensor used in the R53, but no luck. I did find a datasheet for a similar sensor that has a table of thermistor resistance values vs temperature, and an equation for the pressure vs voltage. My guess is the thermistor is going to be exactly the same. The constants for the pressure sensor will need to be adjusted.
There is also a recommended circuit in the datasheet, that I wonder if MINI used in the R53. Would need to know the resistors MINI used to connect to the thermistor to come up with an equation for temperature vs voltage. Below they show a 2.61kOhm and 38.3kOhm with the thermistor connected in the middle. Not the end of the world if this isn't available, can reverse engineer it from a couple of temperature readings from the OBD port.
Had some nice weather today, so proceeded to wire into the TMAP sensor. This was very painful. Its very difficult to push out the existing pins on the 4 wire connector. I cut off the old pins once they were pushed through, fed through 4 new wires and crimped them on the existing wires with new crimps. Some pics below.
TMAP connector in original state. Pins finally pushed out the connector housing, and 4 new wires fed through. new and old wires put in parallel with new crimps. TMAP connector back on the sensor. A couple tie wraps to strain relief the new cable on the old cable.
In order to get accurate data for the gauge, I decided to remove the TMAP connector from the sensor and feed a voltage into the temperature and MAP wires and read the OBD2 values. The plots below show the transfer functions. For MAP it's a linear relationship. For temperature sensor I used a 5th order polynomial to get a very accurate fit.
