95 Jimmy #4 cylinder misfire

[srich]

Hi,
I'm new to this website and would appreciate any help anyone could be. 95 GMC Jimmy 6cyl Vortec. It was running fine, parked and started the next day and it was skipping. That made no sense to me. Checked codes and got P0304. Changed Plugs, wires, fuel filter, added injector cleaner. Drove about 20 miles and still same problem. Pulled new #4 plug dark spot on plug tip, other plugs are fine. Is it possible the coil is faulty even with other cylinders firing correctly. #4 plug is firing well out of the cylinder? Should I buy a coil or what should I do next? Thanks for any help!

[old_master]

Welcome to AF.
Save your money on the coil, it does the same thing for all cylinders. All P0300 series DTC's are usually caused by problems with secondary ignition: spark plugs, plug wires, distributor cap and rotor. The 4.3L is very fussy when it comes to the spark plugs, distributor cap and rotor, use AC Delco only, unless you don't mind having problems. How long has it been since the cap and rotor were replaced? Have you checked fuel pressure and leakdown recently?

[srich]

Originally Posted by old_master

Welcome to AF.
Save your money on the coil, it does the same thing for all cylinders. All P0300 series DTC's are usually caused by problems with secondary ignition: spark plugs, plug wires, distributor cap and rotor. The 4.3L is very fussy when it comes to the spark plugs, distributor cap and rotor, use AC Delco only, unless you don't mind having problems. How long has it been since the cap and rotor were replaced? Have you checked fuel pressure and leakdown recently?

I haven't replaced the rotor and dist cap but I am getting good fire to my plugs. I haven't checked fuel pressure and leakdown and I'm not sure how to do this. If I'm getting good fire to the #4 plug, could there still be a problem with the ignition?

[old_master]

If you haven't replaced the cap and rotor, replace them now...use AC Delco. Make sure to put a dab of silicone dielectric grease on each terminal inside and out of the cap.