hello blazer forum, havent really been active here yet, more on zr2usa but yeah. here i am. and heres my suituation.

i will be researching these codes tonight to try and find the problem. p305 misfire of the #5 cylinder. p0420 catalyst system efficiency below threshold bank 1. this happened on my commute home from work this evening, the SES light came on and flashed a few times. ive also noticed with the warmer weather (90F) my temp is usually @ or just below the 210 mark by the end of my 35 mile commute. i know my cat is probably shot, it rattles and shakes and makes a horrible nose mostly at idle. im thinking that may be the culprit. thinking the p305 was caused by whatever is causing the p0420 code. after minimal research on my may home i saw the possibility of o2 sensors and fuel pressure. any advice of where to start would be greatly appreciated. ive got an obd2 reader that will show live data and all that i just dont know exactly how to decipher all the readouts, or know what they should be. ive been questioning my fuel pump lately as well, it whines pretty loud. any tips or links pointing in the right direction for acceptable readings would be awesome. i really need to learn how to use this scan tool properly. thanks guys.for what its worth i did a full tune up less than 5,000 miles ago. plugs, wires, distributor cap, rotor, coolant temp sensor. im thinking if my cat is the problem it seems like it could be the cause of my running so hot as well. i just drained and somewhat flushed my cooling system less than 2,000 miles ago and refilled with dexcool. although ive yet to install a replacement lower fan shroud, or the fan clutch. that could also have an effect on cooling i suppose. not to mention all the grime (oil, trans fluid) coating the front of my radiator. ****.i havent checked or replaced the egr valve either. guess ill start with pulling the #5 spark plug and see what it looks like. any way to safely clean the front of the rad fins? i should probably just replace it, but ive spent so much money on this truck lately. ive ran across some info on 160 thermostats, dunno how that/if it could help me. off to study.

 

Fix the lower numbered codes first. A misfire can ruin a cat converter.


So start by verifying that your PCM can identify a miss correctly. Monitor all 6 cylinders with your scanner. Are the counts zero or nearly zero on cylinders other than #5. If so, pick one that has counts to zero and start it with the plug wire off the spark plug (be sure to ground the plug wire terminal so spark doesn't jump inside your distributor and affect adjacent terminal). The counts on that cylinder should go up rapidly if misfire detection is working properly. If so, your misfire is real and you can trust there is a real problem on cylinder #5 with the P0305. If not, fix the misfire detection system and see if the P0305 goes away.

Test and report please.