Hey guys, I have researched the site and used its knowledge to fix many a problem so far but I am still encountering an engine issue I cant seem to fix. I own a 2000 blazer 4X4, 4.3L engine. I do not have or use a remote start. The issue I am having is upon acceleration from a complete stop and I am having severe hesitation issues, acting alot like I have bad gas. It will barely accelerate and when it does it does it in spurts, occasionally backfiring (at the engine,not exhaust). After I get going a bit (10+ mph) it smooths out but encounters some acceleration issues again around 50+ mph (not hesitation). It idles fine, and no SES codes are popping up. I am getting bad miles per gallon as well. Here is a list of things I have tried thus far from reading other postings:
Ran numerous full tanks of gas (ethanol and non, tried premium as well)
tried seafoam in case of water in the gas
Replaced the fuel pump a year or so ago
changed fuel filter
changed air filter
cleaned my EGR valve
cleaned my IAC
cleaned throttle body
Cleaned my MAF (made sure it was one that did not have a protective aka oily propety, it was the one suggested on the site.
changed my PCV valve
changed all my spark plugs, harness, and rotor (AC delco per the forum suggestions) plugs did not look fouled, made sure to gap them to spec
checked and replaced all the vacuum lines I could access
had the cat changed approx a year ago
have banged on the cat, no rattle or loose debris noise
I'm stuck and need some help. A mechanic friend of mine suggested unplugging the two o2 sensors at the exhaust "Y" on each side and see if this hleps. He said that the fuel mixture may be too rich and this could be causing the bad miles per gallon and the possible cat issues (the acceleration issues at higher speeds).
Running non ethanol gas in the tank seems to help a bit.
any other ideas would be much appreciated. I feel like the blazer should be running awesome with how much time (and money!!) I have put into it. instead I am trying to figure a way to get rid of it if I cant fix this issue.

 

this seems to only be a problem with 2000 model years, sounds like we might be working on same issue, I'll keep ya updated if i figure anything out

 

thanks, have you tried the o2 sensor unplug? I have been told that the downstream cat o2 sensor doesnt matter but the 2 upstream do.

 

You should check your fuel pressure, I put a non-OEM pump in mine and it did OK for a few months then started acting like it was out of gas and gas mileage dropped a little. Ended up finding slightly low fuel pressure that dropped off when under a half tank and under load. I put in a new Delco Fuel Pump and got my performance and MPGs back.

There are so many stories very similar to mine about aftermarket pumps.