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Misfire and HO2S codes


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I recently noticed my check engine light was on, once I scanned it it came up with the codes P0155 and P0300. A while back I had to engine swap my truck, the engine stayed a 5.3 but the year of the motor changed. Before I did any engine work no check engine light was on (this was a couple of months ago, yes I am aware parts break and need replacement but I'm not sure where to start or if its a programming thing). I have only a one year old exhaust system, along with sensors. I have yet to look and see if any connectors or wires have corroded. In terms of misfire, I have all new spark plugs and wires. I know sometimes misfires are also effected by fuel (I replaced my fuel pump awhile ago). It is and older truck (2006). I was curious if it was because I run 87, what 89 might do, etc. 

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