2000 Silverado 4.8 Misfire

[Aj2no17]

How's it going, I have a 2000 single cab 4.8 Silverado 1500 that has a misfire, gradually revving up the engine you can tell the engine is missing and causes truck to vibrate, and vibration is worse while driving. Has following codes: p0300, p0137, p0141, p0157.  I believe these are codes for random engine misfire and various 02 sensors? If someone could point me in the right direction I would really appreciate it thanks

[Chubbs878]

Check your records for when the truck was last tuned-up and do a smoke test for vacuum leaks. If the spark plugs are old, start off with brand new complete set of 100k mile AC Delco iridiums & a brand new set of stock Delco ignition wires. If you find any cracked tubing, replace all of it. Replace the PCV valve and see what you end up with.  Any sensor/EVAP related codes can be addressed in succession. Start running mid grade fuel  or better if you have been using the lowest octane in the past. I'm not big on fuel treatments since I use the better gasoline, but I suggest that too if the latter applies. Usually O2 sensors & catalytic converter failures are result of long term use 87 octane/ cheap bargain rate fuel that isn't getting burned off efficiently. 

Edited November 26, 2017 by Chubbs878

[Aj2no17]

Thanks for the reply. I recently checked the fuel pressure and it's right where it needs to be, and threw in some NGK platinum spark plugs the old ones were very old. Still have the same problem. The truck does have 240k on it, and I'm almost certain all plugs are firing doing a timing light current check to make sure all coils were firing, and also unplugged 1 coil at a time and there wasnt one of them that DIDNT make a difference. I lightly sprayed carb cleaner around the engine don't think it's a vaccuming leak, the throttle response seems normal although when you give it a good rev it takes a few to return to idle.