One of the best indications of an engines mechanical condition is the compression test. To do it properly you have to test all cylinder and compare between them. There should not be more than 15 psi difference between the highest and the lowest. I don't really pay attention to the actual reading just the difference (ie something wrong with that cylinder.
An even better tool is the flowmeter. Compressed are is run through the cylinder (spark plug hole) at top dead center of the compression stroke (ie both valves are shut). It has a gauge that measures the percentage of air lost. If too much air is leaking by you can listen in the intake (bad intake cylinder), the exhaust (bad exhaust valve) or the crankcase (throught the oil dipstick(bad rings)).
Sometimes you just have to pull the valve cover off and look at things like the rockers and valve springs. I have seen valve springs broken that give a slight miss and put the check engine light on for a bad cylinder. Start with the compression check (easiest) and then go to the more invasive testing. How does the spark plug look from that cylinder? Could it be a shorting ignition wire making an arc by the head? Start with these.
1992 Bonneville SSEi
White, grey Leather interior.
Tinted windows and blackouts on headlights.
Custom high flow exhaust, Everything replaceable - DONE
300 000 kms original engine, tranny 2 rebuilds.
Playboy Bunnies Embossed in Tint. Oh Yah!
Ever Seen a Polar Bear in a Snow Storm?