Are all the phase 1.5 engines (97/98) the same as far as ECU compatability?
I understand that these arent remappable ECUs and PowerFC is the only aftermarket option.
My phase 1.5 in my 98 Forester S/Tb(250PS) says EJ20G on the VIN although I read imprezas of the same timeframe are EJ20K, I believe the 97-98 Foresters carry the same phase 1.5 motor layout thats in the MY98 imprezas, with the rectangular non slanty intercooler, single center coil pack, and a recirc valve thats not attached directly to the intercooler tank.

Are those all using the same ECU setup in general, and are they interchangeable between say, turbo foresters, WRX and STI's of the same time?

 

The ecu plugs and pin layout wise are interchangable between forester and Impreza.. but the maps within are different I believe.. therefore it wouldn't be wise to fit an Impreza OE Ecu to it.. imho.

You can however fit and get mapped a Link or PFC or any other aftermarket ecu for the Impreza.. the cut off dates as to which ecu type the Forester has in it are less defined.. you would need to remove the kick plate and check the number of plugs on the ecu.. I don't THINK they did a phase 1 equivelent Forester ecu but I could be wrong on that.
the Impreza phase ecus would be
phase 1 - 4 plugs
phase 1.5 - 3 plugs
phase 2 - 3 plugs but four sockets on the ecu.. one being blanked.

Simon