Originally Posted by Mike Rainbird
Originally Posted by sailorbob
2.5 bar and 3 bar MAP sensors produce different voltages for the same pressure and you cannot interchange them without getting fuelling problems. Paul, I suggest you source a 2.5 bar to replace the 3 bar asap.
What he said. Basically the MAP sensor divides the boost range into voltage signals from 0 to 5v, so obviously you can see that that fitting the wrong MAP sensor to the wrongly matched EPROM would mean that the ECU would not be seeing true boost.
i.e. 2 bar MAP sensor "sees" 1 bar above atmospheric (0-14.7 psi), this pressure is sent as a voltage signal to the ECU divided between 0-5v.
A 2.5 bar MAP sensor "sees" 1.5 bar above atmospheric (0-22 psi), this pressure is sent as as a voltage signal to the ECU divided between 0-5v.
A 3 bar MAP sensor "sees" 2 bar above atmospheric (0-29.4 psi), this pressure is sent as a voltage signal to the ECU divided between 0-5v.
Obviously running a MAP sensor not fit for purpose (such as in Paul's case), will mean that the car can run lean/rich. This is because when the the car sees it's max boost of 18psi, the EPROM won't see the correct voltage to go with this, and so will under / over-fuel.