Misfire at High Turbo Boost on a Single Cylinder - but coils/plugs OK
My 2007 9-3 2.0T has been throwing a misfire on cylinder 2 for about a year. It happens only at high turbo boost but NOT at high RPMs. In fact, the higher the rpms, the better. I changed plugs immediately and there was no improvement. But it has become increasingly annoying, happening at slightly lower boost levels lately, and in more gears (the car is a manual). It used to be confined to 5th and 6th when asking for boost at highway speeds but I'm feeling it more now. There is no check engine light unless I hold the car in the "misfire zone" and allow it to shudder for about 3-4 seconds. Then I trip a full misfire condition and the ECU seems to shut off a cylinder. The car rough idles and feels like it's running on only 3. The turbo gauge needle swings a little wildly at this point. Check engine light comes on and it is at this point that I will read the cylinder 2 misfire code, that is, if I leave the car running. Shut the car off and restart it and everything resets. It drives normally.
This sounded like an ignition problem / failing coil but I swapped the coils on 2 and 3 and still I'm tripping a misfire on 2. The new plugs, which were properly gapped in the first place, still look OK. I've heard "failing injector" maybe - but I think that would be more systemic across the boost/rpm spectrum. I've heard "vacuum leak", but wouldn't that affect multiple cylinders. MAP sensor - again, would give random cylinder misfires, no? I suppose there could be a problem with a valve on 2 but again, there is nothing at high rpms, and I would think that would show up more then. Maybe, is it worth my replacing wires at this point? Incidentally, cylinder 2 is the last in the firing order for this engine. I don't know if that is relevant.
Any suggestions are much appreciated. Thanks,
Dave
