Hyundai Repair: Check Engine Light, soure, gas cap

Question

Question -
My engine check light has been staying on/flashing the last couple of days and my car has had a hard time starting, especially in the morning. I read here about the fuel filter location and want to change but you mentioned it may be other things. What are they,I want to do the repair myself if I can. I checked my gas cap tightness, I think that was the problem the first time but now I don't think it is.  Thank you.

Answer -
A flashing check engine light is a missfire. Not knowing what model you have I can't tell you much about what to check
Model? Year? Mileage?

More Info-
It's a 2002 Accent, 1.6 engine with 64,000 miles. The flashing is only some times. The check engine light stays on most of the time. It runs a little rough at start up then ok. Could the spark plugs be at least part of the problem?


Answer
Could be the spark plugs.  More frequently, the plug wires arc through the side to the spark plug tubes.  You'll want to give your ignition system a good check.  

Open your hood and remove the spark plug/plug wire cover.  Pull each of the wires off the plug and inspect the tubes for evidence of carbon (from arcing).  If you find any, that's a misfire source.  If you haven't found the soure yet, place each wire back down on the plug without snapping it all the way on.  Now start the car and check for arcing.  If you see none, gradually lift each wire one at a time off the about an inch and place it back.  You're looking for arcing when you do this.  The spark should jump out the end of the wire onto the plug or the plug tube.  If you see arcing at the coil or out the side of the wire, you've found a misfire source.  

You can also use this method to see which cylinder is misfiring if it's misfiring when you're checking it.  If you pull a wire up and the engine doesn't run rougher, that's the misfiring cylinder.  If you don't have any abnormal arcing, you can switch the spark plug with another cylinder.  If the misfire moves with the spark plug, the spark plug is the cause.  If it stays in the same cylinder, then you've got a compression or fuel injector issue.

Also check the porcelain of the spark plug for a vertical black carbon line.  If present, ignition fires down the outside of the porcelain along the carbon line instead of firing the spark plug.

Replace anything that's arcing where it shouldn't be.  I recommend using only factory plug wires.  If your spark plugs are worn or have more than 30,000 miles on them, they should be replaced.  You should replace them with a well-known quality brand such as NGK or Denso.