misfire, diff. from open to closed loop

I have a misfire issue lately. Checking on the scanner, i started the vehicle. In open loop, cylinder 7 was misfiring like crazy. As the vehicle went into closed loop, the misfire switched to cylinder number 2. And it went wild. Did some basic troubleshooting, and i am debating between opti and pcm.

The opti was changed about 4 months ago with a J Cromer unit, so thats a possibilty. But the closed/open issue steers me to pcm. Are there any ideas, or similar situations?

Thanks in advance
john

Mine also reads #7 misfiring the most, with #2 and #5 as occasional. My miss gets worse in closed loop but is always #7. I've read alot of talk about this misfire and tons of guesses but nobody has tried replacing the PCM that I know of. I replaced the opti-spark and it made no difference.

well, iam sending the pcm to bri at pcmforless, and will have an update early next week.

any other suggestions or stories are welcome and appreciated. Thx

john