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What to look for when diagnosing po316 and po303


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I have. 2002 f150 5.4 4x4. Changed ignition coils and spark plugs. Now have code po316 and po303. I’ve swapped first cylinder coil with third cylinder and still comes with po303 so I believe the coils are good. In cylinder 3 I have the auto lite ht1 spark plug. I have 12 volts at the fuel injector connector and using a test light I have power to the coil connector. I’ve swapped both upstream o2 sensors, camshaft position sensor and crank shaft position sensor but did not fix the issue. Also changed the fuel filter. At this point I am not sure what is causing this misfire. Egr valve? Maybe poor combustion in that cylinder? Kind of at a loss of what to look for at this point.

2 Answers

Check the FAQ. Also there's no such code as poXXX. There are 4 numbers.


The misfire on cylinder 3 in your case can be lots of things, from bad injectors to blown head gasket. Before throwing any more parts, have a mechanic scan the car and analyze the data.