Many thanks Autotechpat, Right where you said. Engine is pinging under load and the code said knock sensor. If you don't mind a general question for you- this engine with approx 147K has had what I call a piston slap sound for about the last 20K miles. Its really load when it is cold out and you first start the car. Once the car warms up the slapping nosie goes away. I cal it piston slapping because I am assuming that this is exactly what it is. My logic is that when it is cold the rings are slapping against the worn cylinders. Once the engine warms up and the rings expand, the noise goes away. My question is this-is this common with the 2.5 L engine? My plan is to just let the wife keep on driving it. Your thoughts on this? Thanks again for all fo your help. Jon
Engine issues on 1998 Subaru Legacy
by jaydoll in Hartford, CT on April 19, 2009
ANSWER by patrick mannion , April 19, 2009
Jon. Did your engine at one time run out of oil could it be rod bearing noise you hear? The noise would go away after a few seconds of running once the engine gets oil pressure. Piston slap occurs due to the engine having over heated. (Head gasket problems are common on 2.5 Subaru.) Piston slap is where the side of the piston collapses and causes the piton to flop around in the bore until the piston warms up. I have seen rod bearing noise and piston slap be interpreted by the ECU as engine knock and the ECU then retards the ignition timing. Go ahead and replace knock sensor it is a common problem and let the engine run for 30 seconds or so before driving away from cold start up.