I have been doing some research and found numerous threads about the dreaded P0300 SES code. It seems to me nobody really had an answer on what to do so I wanted to get some advice as well as provide the solution (when I find it) to my problem.

I have a 2000 Blazer with just over 180,000 miles on it. The catalytic converter started to rattle about 2-3 months ago. I tried to do the ol' bang on it and that seemed to quiet the rattle for a few weeks but it came right back. About a week ago I noticed going up hills the Blazer would hesitate around 2,000-2,500 rpms. I found myself having to downshift it into 2nd to make it up the hills. Finally, yesterday on my way home it got really bad. I could barely hit 30mph going up a hill getting home and the SES light began flashing at me. Got home, parked it, and began doing my research. When I am in park and rev the engine up I have no problems. It's only when it's in drive (Good lord it better not be my tranny)

It idles just fine so I don't believe it has a vacuum leak. The fuel pump was replaced less than a year ago so I am thinking it's def not that. The fuel filter hasn't been changed in probably 80,000 plus miles. Plugs and wires were done 6 years ago. I am somewhat good mechanically but am by no means an expert so I am going to do my best on filling you in on what I have done. I am heading out now to work on it. I am thinking that the converter is clogged causing the O2 sensor to trip my SES light.

 

would also maybe do a fresh tune up if its been 6yrs might think about that fuel filter as well also during the tune up look at the dizzy cap and rotor button...probably wouldn't be a bad idea to replace them...may spray carb cleaner around the intake plenum and the intake to just rule out vacuum leak at those areas....I mean its a random misfire code it could be a couple of things to cause it but it having no power is funny unless its randomly missing on all cylinders which I guess could happen never rule nothing out but definitely change those things that haven't been changed in like 80k miles or 6 yrs or so I mean you know lol good luck man

 

just thought to if the converter is clogged it would act like what you describing (no power under load) and also it may have something to do with random misfire cause if exhaust cant get out fuel and air cant get in so just another idea for you

 

leaking fuel pressure regulator? do a fuel pressure and leakdown test

 

Replaced the fuel filter just because it had to be done anyway. Performed a fuel pressure and leakdown test and it seemed to be great. Had 62 psi as I turned the key on and after 10 mins it held at about 52 psi. I know the catalytic converter needs to be replaced anyway so I am going to go ahead and take it off and drive it up and down the road to see if that does anything for me.