I have a 1991 Nissan AD Y10. There is a knock(like misfire) when the engine is advancing. Every time I quickly push the throttle, engine knocks like it does not give response for a moment and then pulls. I tried replacing the carburetor and distributor. No luck with them. I suspect the issue is with the ECU which is fitted on the side right side to the gas paddle. I took the car to several garages and what I heard from them was, ECU does not play any role in connection with the ignition system of this car. I never have opened and checked the engine too. Can someone please help me with this. Anyone who experienced the same problem. Suggesting a good place to diagnose this would be a help too.