My 2011 Silverado 5.3 with 260k miles
Codes: P0172, P0175, P0300
Work completed in the last 1.5 years:
-Heads Rebuilt by Crazed Performance
-Lifters inspected, no issues at the time
-Injectors Replaced
-Evap: Charcoal, Gas Cap, Purge Valve all Replaced (last month)
-Coils, Plugs, Wires
For the passed 1.5+ years the truck has been throwing random misfires that we haven't been able to resolve. Recently, the truck has been hardly drivable at higher loads like uphill especially. You could mash the pedal and the vehicle had zero response.
I am suspecting that the catalytic converts are bad/clogged causing either back pressure, or a problem o2 readings. Longterm fuel trims -18% to -30%
I am leaning towards bad cats, but I'm a little confused because I haven't received any cat efficiency codes p0420. I measured the temp of the cats:
approximate temps (F)
Driver Side: Inlet: 400 Outlet:600
Passenger: Inlet: 400 Outline 500
3rd cat Rattles: Inlet 300 Outlet 300 (No sensors)
ECT for this chart is 190+ the entire time
It's worth noting that the engine was cold here, and hit about 190 when the I got on the gas in the shaded region causing misfire/rich codes
A follow up on this-- I ended up acquiring a bi-directional scanner that allowed me to identify bad injectors. I made the mistake of buying injectors off ebay 1.5 years ago (I was desperate) and it seems that they have caused me a lot of grief.
After running a balance test on the injectors it became quite obvious that they were flowing way too much fuel. Luckily I had my previous injectors which I believe to be OEM factory. I created an injector flush tool to give me reasonable peace of mind that the OEM injectors were relatively clean.
I got it all back together and the first test drive is very promising, no misfires, or rich codes. Truck pulled very well through the power band. I did end getting a shop to knock out the cats, and put a new muffler, so hopefully that doesn't cause any codes to be thrown.
If there a cat rattling and exhaust feels restricted it probably is. The cat that is rattling is the one without a sensor after it so it can't give a code. However, it could be a melted ball that plugs the outlet the moment the throttle is mashed. Try pulling out an front o2 sensor and check for back pressure. Hook up a gauge if you have to. Keep in mind you will have to use a metal tube long enough te get it away from heat before hooking hose up.