Misfires in S2k's fall under a few general rules.
1. A Cylinder specific misfire. If you have one you will see a specific P0301 to P0304 denoting the Cylinder.
2. A random Misfire P0300, It is not cylinder specific., but multiple cylinders.
3. A Multi cylinder misfire, that is more than 1 Cylinder misfire DTC's at the same time.
These are all SAE defined OBDII DTC's. A Cylinder 1 misfire on a S2K or and any car built for the US market since 1996 is required by law to define the DTC the same way. A P0301 on a BMW or a S2K is still a cylinder 1 misfire. Occasionally a cylinder specific misfire is accompanied by a P0300 random misfire or a p1399 temporary misfire DTC. If you let the car run long enough with a P1399 is turns into a permanent DTC, the P0301 to P0304 or a P0300.
Cylinder #1 is closest to the radiator, Cylinder 4 is closest to the firewall. Cylinder order is 1-2-3-4.
I'd like to bring up the ability of the PCM to correctly identify a misfiring cylinder it IS NOT always able to accurately identify the misfiring cylinder, especially if there are more than 1 cylinders misfiring.
A cylinder specific misfire often troubleshooted by moving components, Moving coils, plugs and injectors are all valid tests. If the misfire moves with the component replace the part. You can still have a wiring harness or PCM issue and not a mechanical problem.
If you have a misfire code that is not effected by moving a external component such as a coil, plug or injector The most likely cause of a misfire is either low compression, or valve train damage. = An internal engine problem. On rare instances a wiring or PCM could still be a cause.
If you have multiple cylinder misfire codes it is usually not a component. Multiple component failures are rare.
If the misfire just started after you put gas in and now barely runs it's usually a fuel quality issue.
Cylinders that have low compression misfire. Cylinders with normal compression #'s rarely have high leakdown rates. Normal S2K compression test numbers I have found on cars in service are 200-220Psi.
If you see under 200psi, there is a good probability you will also see a high cylinder leakdown number.
Leaking piston rings, scuffed bores, bent valves and burned valve seats are causes of high leakdown and low compression.
Leaking or burned valve seats has become much more common with higher mileage multiple owner cars than it used to be.
If you have the Freeze frame data from your car, this is only 1 frame of data when the DTC was set. It gives you a basic information of the operating conditions of the engine. Most inexpensive scan tools provide a minimum of data, the more expensive the tool, the more complete the data is.
Fuel trim in Freeze frame data is the adjustment the PCM is using to get back to a 14.7:1 ratio. Since Catalytic converters need to be either slightly rich or lean from 14.7:1 to reduce NOx, an HC and CO from the exhaust the Fuel trim #'s will always be changing when watching on live data from the PCM. The freeze frame is 1 data point at the time of the misfire. Different scan tools will display Fuel trim differently, some use 100%, some use 0 to start. 105 or 5% would be lean from 14.7:1, The PCM will be increasing fuel to the injectors. 95 or -5% would be rich or reducing fuel to the injectors.
Misfiring cylinders do not burn the fuel being injected into them. It is not unusual to see rich Fuel trim #'s The fuel trim is calculated directly from oxygen sensor feedback. If there is excess oxygen in the exhaust the engine did not burn the fuel injected into it. PCM sees the rich condition and reduces fuel.
Here lies the rub, lean cylinders misfire too. You can have a lack of fuel and and get a misfire, and the PCM will add fuel. This is why it is very easy to misread fuel trims to determine the cause of a misfire.
My advice, don't worry with Fuel trim #'s, they are only a small part of the big picture.
Step 1. Swapping components( plugs, coils, injectors) If the Spark plugs are black and sooty there is a source for this, you will need to identify it. low compression will result in a sooty or wet spark plug. If the plug fouled replace it Fouled plugs do not work.
Step 2. If the misfire did not change with a component you need to investigate are the components working in the 1st place? They make test spark plugs that plug into a coil, I highly recommend picking one up. Special tools may be required here! if you are in over your head, STOP. Do not break your car worse. Please do not set your car on fire, or cut an engine harness trying to diagnose it. Butchered engine harnesses make Mechanics very angry.
We charge extra to unf@#k what someone has has f@#ked before we can continue diagnosing your car. You can skip to step 3, but if you don't eliminate all of the possibilities in step 2, your car will still be broken.
Step 3. Perform a compression test, followed by a leakdown test if the compression is low. The leakdown will identify where the compression loss is from. Either the rings and bores, or the valve train.
A word on the random misfire guys and gals,
Your car that sometimes runs ok, but also runs like crap at times. You could have a component failure, or an internal engine issue. Often replacing some parts happens during the diagnosis since your issue comes and goes. Wiring connection issues are rare on a Honda that has not beed screwed with. Unfortunately S2K's have a very high rate of being screwed with. if you had a VAFC, Emanage, an injector swap or a Yellow box, start there. Bad connections often do not present themselves the same way all the time. If you have gone through the component swap dance and nothing has changed, go to step 3.