2000 Kia Sephia misfiring


I have a 2000 Kia Sephia that just recently began to misfire. I got autozone to diagnose the check engine light and it said that cylinder #3 was no good. I should note that i am not an experienced mechanic; this was my first invasive work on a car. but i was prepared, with proper tools and detailed manual. I changed out the spark plugs and the number 3 was indeed covered with gunk, but the problem persisted. in fact, the #3 cylinder was filling up with gas. So i changed the valve cover gasket. I started the car and, for the first time in a long time, it ran like a dream - for about 2 miles, and then the jerking returned and check engine light resumed its blinking. I want to fix this myself, unless thats ridiculous. Anyone have an idea of why this sequence of symptoms would occur? Thanks in advance.


most of the time when the reading shows misfire, it is usually the wires.if changing the plugs and the wires and the problem is still there,it could be the coil if each wire runs to its own coil.if your plugs and wires are bad, you may also want to the all the filters too. sounds like you need a complete tune up.


I am sure the error code was not “cylinder #3 was no good.” It is always best to get the actual code, usually in the format of P0123.

In this case your description tends to make me think a fuel injector is bad and sticking open. I would not want to rule out a bad plug wire however. If you have not changed the plug wires since it was new, it is past due.


This excess fuel is getting there either by a leaking fuel injector or a bad fuel pressure regulator. If the fuel pressure regulator is leaking, it will pour fuel directly into the intake manifold. I don’t know the layout of your Kia but it could be going mostly into the #3 cylinder. Anyway, check the fuel pressure regulator by removing the rubber vacuum hose and check for the presence of fuel.


You are correct. The actual code was p0303


do a compression check on that cylinder also and check for vaccum leaks as these both could lead to a dead cylinder