QuestionI erased the code, and it ran good and stayed off a few days, now it's running really rough at idle and hesitates on take off..the light is back on steady..
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-----Question-----
I have a 2002 Elantra, after the check engine light came on, I ran to advance auto to have them check it. It was code 303 cylinder 3 misfire...after changing the plugs and wires..light was still on..they had me put fuel line cleaner in the tank and still no help....also changed the air filter as well..just can't think where to look next..
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Hi, Jack. Have you disconnected the battery or cleared the code with a code reader or scan tool after repairs? If the lamp isn't cleared, it may not go out for a number of drive cycles (however long it takes the computer to be convinced the problem is gone). If the car went back to running normally, then you probably just need to disconnect the battery for a few seconds to clear the code.
If the lamp comes back on after clearing, then we'll need to investigate further. If we're already at or reach that step let me know.
AnswerOkay, gotcha. Since it changed when you did the work, that suggests it's a secondary ignition problem as well.
First, pull the plugs back out (or the plug on the offending cylinder if you've reverified the code). Inspect for carbon tracking and proper electrode gap. Since these are platinum plugs, you're pretty much looking to make sure the plug wasn't dropped or something causing the gap to close.
If okay, reinstall the plugs and set the wires down onto the plugs, but do not actually clip them onto the plugs. Start the car and then gradually lift each wire off the plug. The spark should come out the end of the wire and jump onto the plug (or side of the tube, depending on how far you pull it out). If it comes out the side of the tube, out of the wire insulation, or out of the coil, that's the location of your problem. If you don't get any spark at all out of the plug end of the wire, then you'll need to find out whether it's lost in the wire, or if the coil is not sparking. If you've got a known good wire-- presumably the old #1 wire would qualify since the misfire was on cylinder #3-- you can substitute that in place of any questionable wire to see if the condition goes away.
Additionally, if you can identify which cylinder is misfiring and you suspect a plug as the cause, you can swap the plug with another and check to see if the misfire changed cylinders accordingly.
