I have a 2004 Sierra 4.3l v6 that has started to run pretty rough on idle like it wants to bog out, I noticed my exhaust tips black (don't know if that matters). I checked the codes and got the P0300 code random misfire. I have replaced the spark plugs and the spark plug wires as well as the ignition coil, distributor and the distributor cap. That did not seem to solve the problem and I've ran out of ideas. Anyone might have some insight on what it could be that is causing this P0300 code?

 

You said the motor is running rough. That WIIL set off the P0300 code. Most likely a fuel injection issue. You'll need to run a diagnostic scan on it. It would also be wise to check fuel pressure and a multi-cylinder compression test.

If you've been running cheap gasoline, it's likely you have an injector issue. It does not matter what the fuel station companies claim about being "clean" and "Top Tier," and never buy gasoline at a "mom & pop station".

Yes, black-colored exhaust means you are running rich. Eventually your catalytic converter will be destroyed.

 

yes I changed out the spider injectors and one of the injectors had a crack on it but truck continues to misfire. A buddy ran a diagnostic scan on it and it shows cylinders 2,4,6 are misfiring. He thinks it could be the distributor itself or the cats or o2 sensors. Could the o2 sensors and cats cause it to misfire? I replaced them 2 years ago. And what about the distributor itself?

 

All of those could cause a misfire. Your ignition control module could as well.

 

Did you ever figure out the issue