[scoobypat]

as per title, I've a 1993 wrx, had to change the up pipe. Car went well for a couple of days then, I put my foot down to pull out of a side road got to 3000rpm car noise dived and plumes of black smoke came out of exhaust. Then car was lumpy and hard to keep going... WHEN CAR IS STARTED COLD SOUNDS OK, But when warm is lumpy. disconnected cam and crank sensors, turn it over so it does fire up not, and sounds fine, no piston slap or any other sounds. don't know what else to do as tried compression test. all 4 cylinder's the same