I have an 01 LT Blazer 4x4, I'm getting the famous P0300 and P0420 codes even after changing my cap, rotor, wires, and plugs. All AC Delco. I cleaned my EGR and MAF just like the DIY told me. I have to crank it for a few seconds just to get it to start and then it has a rough idle, some black smoke if I rev it up, and smells bad. When it shifts between 1st and 2nd, and when accelerating to pass somebody, it sputters as if I'm hitting the rev limiter. Can anyone help???

 

Sounds like a bad cat for starters. Then since you replaced everything else I would suspect a worn out distributor or bad coil. Check the rortor to make sure it isn't arching, new parts can fail. Could also be the throttle position sensor.

 

If it was a bad coil or distributor would my plugs be fouled out? They didn't look bad at all when I changed them today.

 

not nesessarily. My gears were worn on my dist. I ordered a skip white unit off ebay, came with the cap and rotor. Took care of my misfire issues after I already replaced the same items you did. It came with accel parts, I swaped em for my delcos though. I did a review of it awhile ago. I was impressed with the distributor, all aluminum instead of plastic.

 

I agree with it being a bad cat. Possibly a dying fuel pump, also.

 

+1, wouldn't hurt to do a fuel pressure and leakdown test just to rule out the possibility. Autozone has em that you put a deposit down then get it back when you are done.

 

Or pay 40 for the cheap one and keep it for next time. Because there will be a next time, especially if you have an Airtex pump.

 

I'm gonna try to test the fuel pressure. I'm worried it might just be that damn Airtex pump. I do remember that about 2 weeks after I installed the pump is when I was having trouble starting...

 

Ahh, I would be willing to bet its the pump. Stick with delphi or delco. airtex is garbage.

 

I've bought a couple of OEM pumps from a guy called "Mr Fuel Pump" on Ebay. They were priced right. It's worth looking into if you go that route.