Hi was just wondering about a couple things.I have had a couple codes come up and have changed all plugs and coil packs now it showing a power steering pressure switch and misfire on num 3 can the p/s switch cause a misfire thanks for reading.
No, the power steering pressure switch cannot cause a misfire. It is used as part of the idle control system; it lets the ECM know when the power steering is putting a load on the engine so that it can bump up the engine idle accordingly via the idle control circuit.
Anything that can cause a misfire on # 3 will cause a DTC P0303. That can include a bad plug, coil pack, fuel injector, open/shorted circuit on either the coil or fuel injector circuits, intake leak at # 3 intake runner, mechanical issue such as low compression at # 3 cylinder (bad head gasket, burnt/bent valve, etc.). You haven't given us any information as to what year/model vehicle nor engine you have, so it's tough to assist you any further. The factory service manual has a step by step procedure for P0303 in the engine control section.