I have a 03 blazer xtreme that i recently replaced the engine with a used motor that has 60k on it because the one i had had bad compression on a cyl. Well ive basically replaced everything on this engine now and im having a P0300 code on highway speeds that flashes and slight miss at idle. Now ive replaced fuel pump, mass air flow, fuel injection spider assembly, all ign parts, ign coil and module, cleaned throttle, new battery, belt, fuel filter, air intake system, the works. The one thing i didnt use OEM parts were the plug wires and intake pressure sensor on the upper plastic intake. Ive checked compression and oil pressure and all are perfect. Now when your driving around town its fine but when you try to hammer the gas and have some fun with it it feels like it hits a wall and has hardly any power. Oh ive also replaced exhaust and cat. Now i took it to a shop locally and he says it only has misfire counts on cyl. 1 and 4. He recommends that those cylinders has weak valve springs or might be bad spark plug wires. Now he has quoted me $315 to change valve springs on those two cylinders or should i replace my plug wires with a new set of OEM AC Delco wires? Im stuck and basically out of money and dont really know what to do.

 

Random misfire is almost always due to a fault in secondary ingition (plugs, wires, cap, rotor and coil) these trucks are very picky about OEM only

 

thats what ive heard, plus ive noticed the wires i used were 7mm and the AC Delco wires are 8mm. Would that cause lack of power and likely why only two cylinders have misfire counts the other ones all had zero misfire counts.

 

Well, the delco wires are built to better spec. Make sure you use dialectic grease on the ends of the wires, both where it seats to the plug and the cap. And make sure they are seated all of the way.

 

I have had the same issue with mine since i have bouight the truck.....and changes all the same parts, I will have to try the ac delco thing. I just had to replace the purge valve on the intake for the charcoal canister to get rid of the gas smell. Mine still was gettting pretty good gas milage so I didnt stress it to much

 

Run a compression test, engine cold, mine had 3 valves broken.
Before the same code's.