2001 Hyundai Elantra P0304 Misfire Cyl 4

I have replaced the plugs and tested the coil pack, plug cables—those are showing normal readings. Searchers have lead me to checking the fuel injector(s) for clogging but I cannot find how to do that. Any suggestions.

That car is very partial to NGK spark plugs. It is also notorious for oil seeping into the spark plug well. Re injectors, touch each injector and compare the sensations. Beyond these, how mechanically inclined and equipped are you?

I did not replace the plugs with NGK but since the probelm did not go awy with the new plugs I will not worry about it until after teh solution is in place. All plug wells looked clean.
Re injectors: I have never dealt with injectors ( I am used to old school carborators). I am fairly mechanically inclined and okay on the equipment side of the world. I guess first I need to know how to access the injectors to test for clogging.

The most common way to test injectors for the DIY is switch positions and see if the miss fire moves with the injector. But first, can you test the compression and while the plug is out inspect it for damage and fouling. Also, how did you test the coil. It’s a wasted spark system as I recall and a coil can fire one end and not the other.

Never attempt to flow test injectors without proper equipment.

Another quick way to check for a faulty injector is to use a mechanics stethoscope. Place the probe on the injector and it should make a sharp clicking noise. If it makes more of a dull thudding noise that injector is suspect. Or you can use the which one doesn’t sound like the others approach.


I was able to test the coils and the plug wires with an OHM meter and all had acceptable readings. I will give the injectors a listen and see what I come up.

Be aware that coil resistance checks will not catch internal high-voltage breakdown failures that coils can experience.