andymac

Hi,
Can anybody tell me where (if?) there is an ELECTRONIC pressure sensor for turbo pressure. I'm assuming that there is one so that the ECU can do whatever it needs to do with overboost etc. What kind of output is there from it (range, Kpa/mv etc., etc)

Thanks in advance...

cheers

Andy

R19KET

Andy,

The boost map sensor is located,close to the solenoid.It's flat,1.5" x 1.5" x .5" aprox'.3 wire plug.
If you check all of the hoses going to that area,you'll find it.Sti4,anyway.

Sorry don't know what the output is,sensors are normally 1 > 5 volts.David at PE knows.

Being a nosey b*st*a*d,what are you trying to do ?
Hope this helps,

Mark.

andymac

Hi,
Thanks for the info. I'll let you know once I've "progressed" it...

cheers

Andy

R19KET

Spoilsport !!!!!!! OK.Let me know.

Mark.

alanp

Andy

The MAP (Manifold Absolute Pressure) sensor has a fairly high output impedance so be careful how you load it. If you connect any series or shunt resistance to the output you will affect the values fed back to the ECU. Better to use a buffer amp. I have characterized one and found it to be pretty linear. Here are some tabulated values.

MAP Output
(psi) (V)
-9.7 1.26
-7.7 1.45
0.0 2.31
5.0 2.63
10.0 3.15
13.5
15.0 3.71
17.5
18.0 4.04
18.5
19.5
20.0 4.25
25.0 4.78
27.5 5.03

Hope you find this useful.

Alan


P.S. The supply to the MAP sensor is +5V and not +12V.

andymac

Hi Alan,
Thanks for the info - exactly what I'm looking for. This should give some hints to the other people in the thread.

I'll let you all know how it's going on...

cheers

Andy

andymac

Alan,
Sorry forgot to add, Impedance or Resistance ? (I'm presuming here it's running off 5V DC) Any idea of what it is ?

thanks

Andy

Bob Rawle

Alanp, do you have the info on the connector pin outs for the map sensor ie cable colour and function

Bob

Colin

Interesting to see other people up to technical things. The characteristics of my UK MY97 are pretty similar to Alan's:

Pressure / Voltage
-10 / 1.28
-5 / 1.8
0 / 2.3
5 / 2.8
10 / 3.3
15 / 3.9
16/ 4.0 (4.0 = overboost engine cut)
17 / 4.1
then becomes non-linear approaching 20psi.

The output wire is yellow with a black stripe and silver dots. It's uniquely colour coded, so easy to find at the ECU end. If you want to do anything with this signal, you'll need to buffer the signal via a high impedance op-amp because, as Alan points, its output impedance is probably quite high. Note also the ECU uses this input for the ignition retard map. Some more info on www.force8.demon.co.uk/impreza.

Come on Andy - give us a clue what you're up to! Or we'll be forced to guess. My guesses are:

1. To build a circuit to remove (or raise) overboost cutout? (Then add a bleed valve and you have a so called "superchips" solution.)
2. Attenuate the signal, in the hope the ECU provides more boost, via the closed loop feedback (which it will to a certain limited extent).
3. Build an electronic boost pressure gauge?

alanp

Andy

I don't have the numbers to hand but the circuit resistances are quite high namely kilohms, not just a few ohms. The MAP sensor has to sink current from the ECU too. If you were thinking of introducing a potential divider between the MAP sensor and the ECU I can tell you it will not work properly. The MAP sensor needs to be buffered by an amplifier to avoid loading it.


Bob

The wiring colours are:-

+5V Red/Silver
MAP Output Yellow/Black Middle Pin
0V Black/Yellow

Regards

Alan

andymac

Ok, Ok. Here's what I'd like to do. I'm sure this is possible and if it was just a case of monitoring it for testing purposes, (in my previous engineering capacity) then that would be easy enough. However, what I'd like to do is...

(1) Use the MAP sensor to read the pressure in the manifold to provide me with a boost signal
(2) The reading would be "piggybacked" / run parallel (suitably configured) so as not to interfere with the normal running of the system
(3) Use this output voltage to drive a small IC to display this output digitally on a small LED.

Now the important bit.
There's a perfectly good place to put this output and that's where the digital clock is (not sure about <98MY). It's nice and in-line and visible. It also has two button holes which (given the technical knowhow) could be used to provide buttons for "start max boost sensed" and "reset max boost sensed" so as to provide an additional usage (although I realise this is going to be more difficult).

So questions are;
(1) is this feasable
(2) how easy would the circuitry be to build
(3) exacltly how much would it invalidate my warrenty !!!
(4) how easy would it be to replace the clock
(5) are there any better places to put the display where it doesn't look like an aftermarket add-on

The other option is to write an interface to the ECU via the serial connector (RS432? RS232C can't remember) from a suitable PC and then get a Windows CE / Psion 5 or whatever mounted in the car to display all the parameters in real time (like the skyline - very cool)

Cheers and thanks for all your help so far,

Andy

P.S. This all depends if the missus will let me "fiddle" with the car !

Dippy

I guess that the MAP sensor will either contain a temperator sensor for compensation or else the ECU will make that compensation based on its own temperature readings? If it has a high o/p impedance then the latter is probably true.

You may have a problem that if your op-amp is not right next to the sensor, then you might get noise problems. But if the op-amp is next to the sensor then you'll have to include temperature compensation.

Solid state pressure sensors are cheap so why not just run a pipe to one on the other side of the bulkhead?

I too am thinking of using the clock's own display as a digital boost guage, so I'll let you know if I get anywhere.

Regarding using the ECU's serial data, I found a website in Japan from someone who had done a lot work in this area. I think the URL is

dmel

Does anyone remember the address of the web site which shows the positions of all sensors in the Subaru's engine bay?

Dimitris.

GavinP

The diagram is in the back of the Link manual -