Misfire at High Turbo Boost on a Single Cylinder - but coils/plugs OK

[dscrofani]

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

[Saabian]

I had the same problem. Wat fixed the problem for me. Replaced the boost pressure valve, the bad coil, and put NGK iridium's and it's very important that they are gaped at 0,8 or 0,7 mm. Hope to be of help.

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