Chevy V6 4.3 with 281k miles. It recently threw a misfire code isolated to cylinder #3. The misfire seems systematic and not random, though, as it idles rough. I've got an open question on it already, but I have more info and hopefully a better question.
For a baseline I compared the #1 cylinder to the misfiring #3. The spark plug from #1 looked great given its age, and with all the other plugs remaining in place, that cylinder registered 124 psi of compression. Next I pulled the plug from the #3, which also looked fine (not black, not oily, but somewhere between "normal" and "overheated" compared to the chart here) and its compression registered at 70 psi, and which is definitely a problem. I disconnected and reconnected the equipment and got the same measurement on a second test.
Unfortunately these plugs install horizontally so I'm not sure how to confidently perform a "wet compression test" since the oil won't necessarily flow down or evenly coat the piston..
But there is no smoke in the exhaust. None. And I feel like that's a key detail.
Based on the above, is this most likely an issue with valves controlling cylinder #3? If so ..would this be more characteristic of a bent or a stuck valve? ......if the latter (stuck), is there anything I can try to do to "un-stick" the valve without necessarily disassembling the head??