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2003 grand am #2 misfire

03 Pontiac Grand AM 4cyl, 2.2L, ?Service Engine Soon? light some time on and off. Code come up was P0302 ? cylinder 2 misfire. I checked many areas, such as NEW autolite spark plug, list injector clicking sound, etc. Could not determined the problem. More interesting, every time I filled full tank of gasoline (midgrade). The light was on with 10 seconds and developed with a rough idle after I started engine. Some time the light will off after day or two drive. Any one knows why?

How many times has the light actually come on and of those times how many times did you actually get the codes read? I ask b/c if you’ve had the codes read multiple times and consistently come up with P0302 then I’d say to stay on the 2nd cylinder - specifically check the compression just to rule out mechanical fault before chasing your tail about other things.

But if you’ve only had the codes read once, but the light and rough running have occurred multiple times I’d actually worry more about the connection to refueling and rough running. One possibility is that you overfill your gas tank (continue past when it clicks off) and/or have a bad vent valve in the tank. After filling you may end up with liquid fuel in your evaporation lines which then causes the engine to run too rich after you start it up. In this case, maybe one time the code is P0302, another time P0301 or P0300 or even an evap system code.

Is the check engine light always associated with refueling?

Many times the reader were display same code P0302. You mean that may not injector problem. How to check the compression? What other areas may need to be check? Thank you.

Compression is checked with a compression tester/gauge. You can buy them or major auto parts chains may have them as part of “loaner” tool sets.

You need 4 things to make the thing fire - gas, air, compression, spark. For a single cylinder misfire, put air at the bottom of the list. Lots of people spend a lot of time and money chasing spark and fuel. Its often good to just rule out a compression problem before chasing those things.

If the compression is ok, you need to worry not only about the spark plugs but also the wires & coil/coil pack/distributor (whatever the set up is). Then you also need to worry about the injectors. You can swap the #2 injector with another one to see if the misfire moves with the injector. On the fuel end, you have to keep in mind that a misfire can come from either too little fuel or too much.

A repair manual for the car will help you in sorting these things out.

Thank you for your great inputs. For the past several days, I get more information. The light was on WHEN the gas tank was full. The light will off when has a 3/4 or less of gas left in the tank. Do you think I need check the gas pressure sensor, vent valve or even gas tank cap (cap was replaced with new OEM before)?

That is rather strange if your code is always a cylinder 2 misfire. Try driving around for about 1000 miles or so never filling the tank all the way. Just keep it at 3/4 or less and see what happens.