So I recently installed a new engine in my truck before driving it across country from FL to CA. Halfway through my trip my check engine light started coming on. Initially I had a P0153 followed by a P0154 and now a P0300. I guess my sensor slowly crapped out on me as I went through the trip. The questions is why? Both sensors were replaced when I replaced the engine. I put about 2000 miles on the engine before the trip with no problems. The post-cat sensors are turned off by the tune.

On a side note I have a mysterious coolant leak coming from the area around the front of the driver's side head. I have no idea where since its hidden by the alternator bracket. I've pumped it up to 20lbs with a coolant pressure tester with no leaks! It will only leak when its running.

P0300 - Random/Multiple Cylinder Misfire Detected
P0153 - O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)
P0154 - O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)

 

Have you looked to see if any of your wires (plugs and O2's) are burnt from resting or getting to close to the headers? I know my sparkplug wires were gone on mine after a few hundred miles (my fault) and it started throwing the P0300 code. Although it did sound cool at idle () I had to change the wires and route them away from the headers.

 

yeh the 300 code is more than like a short in your plug wires or one not on all the way.

The other codes are pretty typical when doing headers. Your o2's aren't getting enough heat now to be in their "prime" operating mode. Do some searching on the site for remedies for this as there are quite a few ways to handle this (not all work everytime). Hotter heaters in sensors to wrapping headers to making changes in the tune. Surprised you are only getting codes on one bank (#2). Don't be surprised when the bank #1 codes start popping up.