ok, so lets start with this. i have a 2002 chevy blazer 2x4 with the 4.3 vortec with about 170,000 on it. i have a bad misfire, hard start, and a random stall. i have replaced the coil plugs wires fuel pump dissy cap and rotor. i know the spyder could be bad but it tested good. (pulled the upper intake and its dry)

the thing i do not get is it has the misfire under 2,500 rpm anything about that it runs good. i took a video of it ( ) any help will help with this thing... i'm only 17 and cant aford much more parts for the thing... the fuel pressure is good. (has 60 key on and holds 55 for 45 mins.) Help please...... im stumped...

 

unplug the maf sensor (square silver thing on the air filter tube) and see if it runs any better

 

i have and it ran better for a second or two then ran worse and chugged black smoke, witch i'm assuming it is un-burnt fuel.

 

this is how it starts cold.
its usually harder to start then this. but you know how it goes with trying to video tape something. works perfect on camera and not off.

 

I tried stalking your youtube channel to get an idea of what state you're in, but I couldn't tell. I'm in Michigan, and my 4.3 has 185k on it. As soon as the temperatures went below 40 degreesish, my engine started missing and idling rough too. I'd seen this before on other GM engines. I ordered two AC Delco O2 sensors from Rockauto.com (they're literally less than half the price there compared to the auto parts stores for O2 sensors) put them on, and the engine ran smoother than I can ever remember (bought the truck at 150k). An O2 sensor that's going bad will sometimes cause PO171, PO174, PO300, or a combination of any/all of those. Sometimes it wont throw a code at all. But you're at 170k, so it would be worth replacing your O2 sensors anyway if you haven't already.

 

i just moved from michigan, i live in mississippi. the truck has no cat on it so i dont know if that will cause it, but the o2's tested good. i dont get this because usualy the trucks who have a misfire would have it all the way throught the RPM range and this only has it on low RPM's (idle-2,450) the cheak engine light flashes to. i put a new coil on it and it helped for about 5 minunits. then it was back. im literary stumped with this engine. im about to say F*** it and throw a 350 vortec in it.