i am SICK of spooling to 8-10 psi at part throttle, running .1ish for oxygen sensor voltages, and not having any power, then when my ECU decides it's time to enrichen the mixture i get a surge of power at a quite random time.

i know the J&S knock sensor is "supposely" going to be released soon forcing the ECU into open loop mode when 0 psi is achieved, but i'm not going to wait for it, just like i'm no longer waiting for the ERT downpipe. hell will freeze over before the ERT downpipe is released.

i stole the TPS idea from the J&S thread, and i'm currently working on my own circut to do the same thing. i've started from scratch. i bet someone else out there has done this, but hell, i've searched and searched and i've never found anything.

so far, i've come up with this ghetto schematic:



so what's happening here? i decided to use the motorola mpx4250ap pressure sensor that corbin uses for his "fooling the AFC" mod. +5 volts is supplied to it via a 12 -> 5 volt regulator (powered off of key on power). the output of the pressure sensor happens to be almost exactly 1.8 volts at 14.7 above absolute or 0 psi of boost. it would be nice to be able to hook that directly up to a relay, but there aren't any relays out there that switch exactly at 1.8 volts. so, i'm going to feed the Vout signal from the pressure sensor to some type of amplifier circut (which i have been designing today at work) which will produce no output below a 1.8 volt input, and once that point is reached (and everything above it) it will output 5 volts to trigger the 5 volt relay that i have obtained. this relay will force the ECU to connect to a 1.4k ohm resistor (happens to be the resistance of the TPS at full throttle) instead of the TPS.

a few snags i've noticed so far:

1. the pressure sensor is very sensetive to voltage input. it needs to see EXACTLY 5 volts for the output to be accurate at all.

2. the pressure sensor only uses up 5ma, therefore the output signal must be less than or equal to 5ma. it takes a lot more than 5ma to trip on the relay (72ma specificially) that i have. the relay has an impedance of about 68 ohms... so i'm going to need to design an amplifier circut that uses a FET (Field Effect Transistor) which have very large input impediances (in order to not draw any current from the Vout, drawing current from the Vout will alter the output voltage and that's a no-no)

if i get this thing to work, i might consider selling kits if anyone is interested.

discuss.

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)