My 2001 Blazer Xtreme only misfires when I go uphill, at first it would only misfire when I would go 55mph or more and now its 45mph or more, I can go 30mph uphill and no misfire but once I go 45 or higher it will misfire a bunch, I have replaced my spark plugs, spark plug coils, distributor cap, fuel injectors and my 02 Sensors (my 02 Sensors where sending codes, which is why I replaced them) I don't know where to look because I have spent a lot of money on this car and I want to try looking for easy solutions before spending more money.

 

The best general advice is to try to diagnose the issue as best as possible first.

To do that, you will need all the codes that have been set. Then report them back hear and those with more experience than I can help.

All that said, when the O2 sensors throw codes, a possible issue would be air to fuel mixture.

What color were your O2 sensors? Were they covered in carbon? If so a possible issue could be an overly rich mixture possibly due to a fuel leak under the plenum.

 

My first code was a misfire in cylinder #3 which is when I decided to buy all new spark plugs and after I put all those in, my 02 Sensors through codes and it started to waste fuel, after I replaced all my 02 sensors it started to send a P0300 code which meant it was a random misfire and so I replaced my spark plug coils, distributor cap and my fuel injectors, and after all of that it is still sending random misfire codes, the person that owned the car before me use to put lucas fuel injector cleaner every time they filled up on gas if that could possibly mean anything.

 

I have little experieexperience with these specific symptoms and I'm traveling at the moment which has me away from my gm service manuals.

You wrote "I replaced my spark plug coils, distributor cap and my fuel injectors."

Did you also replace the rotor? Did you use gm cap and rotor? The conventional wisdom is that only gm rotors and caps can be relied on. What did the rotor and cap look like? Any weird patterns? How was the free-play in the distributor shaft? Could it move side to side?

You also mentioned replacing the spark plug coils. This doesn't sound right to me. Isn't there just one coil? Did you also replace the spark plug wires?

Finally can you expand on what you meant by what you did with your fuel inhectors? Did you replace the whole fuel injection assembly under the plenum?

Did you know why the previous owner used fuel injector cleaner?

 

I have not replaced the rotor only the cap and I did use a gm cap, the old cap had looked like it was shorting on the third cylinder, yes I also replaced the spark plug wires, the first fuel injector had been messing up but since it was a spider injector, I had to replace all 6 so I did take off the plenum and put a new spider injector, the previous owner just liked to use fuel injector cleaner in any car they owned whenever they filled up on gas but it could have also been in the hopes of cleaning the first fuel injector so it would work correctly.

 

The parts cannon can actually cause more problems, especially if perfectly good AC Delco electrical/fuel system parts are replaced with aftermarket off brand parts. Many a spider/fuel pump/ignition parts have come right back out shortly after install here.

In order to make sure that you are not chasing ghosts the first two things are to get CMP retard within spec and then do the fuel pressure test in the sticky.