Communicating with car's ecu with arduino

Hello, my goal is to read data from the car's ecu with arduino. Tried via OBD, no success, because ECU is not OBDII/EOBD compiliant... But somehow I could read data from the ECU's pins, for example there is fuel consumption pin and somehow i could read data from that pin? And if yes, then how to decode it? Car's oldschool board computer reads fuel consumption data from the ecu, so it should be possible...

It might be possible, but you will have to be extremely knowledgeable about the ECU you are working with. You will need to provide detailed information about your ECU to figure out how the arduino might be interfaced.

model of the ecu with i will be working with: bosch edc15c5 (controls euro 2 2.4Jtd engine). For example, rpm signal is 12v pulses... other signals i guess should be similar

Just had a quick read up and it would seem most people read from the “K” line whatever that is or install a small module that gives them some form of serial data.

Maybe that aspect is worth looking into ?

I've tried to connect to k line via elm327, but got incorrect data with standart OBDII PIDs. I suppose fiat made custom PIDs because software such as fiatecuscan or alfaobd reads data correctly when Torque, OBDdoctor and other apps could not read data correctly...