The engine and exhaust kept having "popping" sound, which something similar to those Subaru's boxer engine. At first, I thought it was the ignition cable and spark plug causing the issue. Which causing the engine to miss-fire and one of the piston does not working but this is not the true story. Thus during these holidays, I tried to swap back all my parts to stock parts which included turbo, exhaust manifold, throttle, ignition cables and even the ECU. However with all these changes, the problem still exist.