Nissan Repair: Rough running..., nissan altima, leakdown test

Question
I have a 2000 nissan altima. I keep getting a code that says I have a misfire. The #4 cylinder is the one, or at least I have had code on it. The spark plugs look black on all of the plugs. The cylinder #4 plug, has oil on the washer ring but is black on the tip like the others. When I take the plug out after running I can smell gas in the cylinder. The other don't smell like this. I think it may be a injector, but would like to hear your expert advice. Thanks.  

Answer
Daniel,

Yes, it sounds like the injector on number 4 is defective.  You can perform a leakdown test and see if the injector is leaking.  I would make sure that the cap, rotor, and wires are are all in good condition too.  But, if you check the injectors with a pressure gauge by turning on the key and noting the fuel pressure and then turning the key off the pressure should remain for a minute or two.  If the pressure drops off instantly then you know that the injector is leaking.