Stone stock 04 Chevy Avalanche 4WD with 5.3L V8 base package, no aftermarket anything, 200K miles. Current codes are P0449 Evap and P0300 misfire. I had knock sensor code earlier; have since replaced BOTH sensors with OEM including the harness, but did NOT do the intake gasket that day. I now have a new one and will be putting it on this weekend.
I've also got a new Evap solenoid and valve coming and will replace at the same time, as well as check the canister for blockage or water; saw a TSB about water in the canister for 5.3's. The P0300 random misfires happen consistently on #2 & 7 at idle but on the road at speed they go away. Also, while watching the data stream at idle you can see that periodically the misfires just drop off almost to 0, then come back up again.
We put a set of "noid" lights on the injector bank to see if they were firing differently. All appeared to be even and consistent. So we swapped one at a time "simple components with their near neighbor; # 4 for 2 and #5 for 7. We swapped plugs, wires, coil; injectors; it always stays 2 and 7.
That should rule those components out. It had a hard starting issue and thought there was bleed-off in the fuel pressure, so fuel regulator. On this model that is in the gas tank as part of an entire assembly; regulator, sensor, pump, and sender. So those are all new; and didn't fix the problem.
We then tested for blocked cat-converters. We pulled the 02 sensors figuring that may relieve any back pressure and validate bad cats. Nope; Ran very loud, but still have the problem. Then we tried to locate any vacuum leaks using a can of carb cleaner sprayed all around in the engine bay. No dice; no matter what, it didn't change the RPM's. In fact, we even watched the data stream on the scan tool and saw no effect on the misfire rate. What to do? Please help!!
