changed plugs,cap,rotor,wires.removed throttle body and cleaned.changed fuel filter and fuel pump.truck runs rough until it gets warm.back firing and missing! plz help!..ive always been a Chevy man...I got a really good deal on this 2 door blazer!...but now with this problem? it makes me cry that i sold my 72 elcamino..loaded with a stroked motor and never once left me stranded.its not like i can slap a HEI in it and hual butt...hahahahabut im not giving up! I love my little 2000 blazer..Drove it for 2 years with a bad sending unit and finally got around to changing the fuel pump,and now i dont have to write the mileage down anymore but,with 98,000 miles? am concerned...Any help will be appreciated!...GO CHEVY!!! woooo hoooo

 

Here are links to the trouble codes you have received:
P030x - Random/Multiple Cylinder Misfire Detected
P0452 - Evaporative Emission Control System Pressure Sensor Low Input

What brand of parts did you use? These trucks are very partial to AC Delco caps & rotors. For plugs, AC Delco or NGK double platinum plugs are preferred unless you have the money for the premium iridium plugs.

 

I used all ac delco parts,BUT i noticed that when i dropped the tank to put the pump in? the little box below the gas door that has marked fuel lins going to it(im thinking this is the evaporator) one of the lines looked like it has been wearing against a bolt and you can see a half moon shape wear in the line..there marked caution fuel lines!

 

That is the charcoal canister. If you have a leak in one of those lines, it could cause the P0452 code. I don't think that is causing your P0300 code, but if you can see a hole, patch it up and make sure that it isn't going to rub through again.

 

any suggestions on how to patch?..wouldn't it leak gas if it rubbed all the way through?..some one told me the 300 code may be a bad gas cap!....swartlkk! i really appreciate all the help.Im a licsensed plumber for dade county,miami.If you ever need any plumbing issues answerd? please don't hesitate to ask me!

I see that your a very busy!...Thank you for all your help! I got the links you gave me...Again!!! any help i can be to you? please let me know!

 

A P0300 wouldn't be caused by a bad gas cap.

The lines going in & out of the charcoal canister are vapor lines only. They should not contain liquid gasoline.