sounds just like my engine. I believe that it is spark knock like a mofo. Check your Crank Position Sensor. Mine simply broke while in the engine so the ECM didn't know when to send spark and eventually busted my piston Be careful removing it cause it may simply break off the rest of the way and fall into the crankcase. You might be able to check it by testing the amount of microvolts going to the ICM from the sensor.