I have a 1991 Subaru liberty with an EJ22 engine. It has a manual transmission.
When under sustained load (accelerating up a hill) it loses power and RPM starts to decrease. If I try and accelerate through the power loss, the engine only loses more power. Changing down gears also does not help the problem.
When it starts to lose power, if I pull over, the engine vibrates and feels like it is running on 3 cylinders. No codes are displayed at any time.
If I let the engine idle for a few minutes, the engine recovers and performs as per normal.
I have replaced the following items:
Fuel Pressure Regulator
I have also run it on 98 Octane Fuel. I have run an upper engine cleaner through it and a fuel cleaner through it.
It has had multiple oil changes.
Does any one have any suggestions to the problem. I have done a significant amount of study and no one seems to have a comprehensive answer.