Some things I do when dealing with problems similar to yours: I eliminate mechanical causes...lifters, valves, etc. Perform a relative compression test. When I am satisfied the engine is mechanically sound I move on to the fuel system...fuel pressure both at idle and when driving down the road, specifically when duplicating problem. Scope injectors. Perform a injector balance test. A faulty injector will quickly become apparent during this test. It is important to note that after performing an injector balance test that the vehicle be started and run to burn off the fuel that will accumulate in the cylinders during the test. I also like to run a injector kill test from time to time. Once I have eliminated fuel delivery and injector function as the cause I move on to secondary ignition. Visually check for arcing or faulty components. Simply put, current is alot like water...it will flow to the path of least resistance. If your secondary ignition can find a path to ground thats easier than the path it takes from coil to spark plug, it will follow that path. This is more pronounced under load. I like to monitor fuel trims when looking for secondary ignition issues. STFT should remain relatively low, +/- 5% up to 8%. LTFT should show a relatively steady reading of around 10% up to 14%. Try and keep the PID list down to 4 selected items to ensure a quicker data refresh rate. A weak or intermittent secondary ignition fault will show up as higher fuel trims. Once you have pinpointed your problem and correct it, I highly recommend clearing your KAM. The PCM has learned a strategy based on the conditions you have been driving your car under with the misfire. Dump that garbage and let your PCM relearn a strategy based on a properly performing engine.
Originally Posted by Beelzeboul
