I have a 1999 ford explorer and the check engine light came on. I used my code checker and discovered the cam sensor was bad. After replacing the cam sensor and the synchronizer it cured the problem. But now when I turn on the heater or A/C it starts missing and check engine light comes back on saying the cam sensor is bad???

SOURCE: Code #P0171 & code #P0174

The most common problem on a Ford with these codes is deteriorated PCV hoses. Check the hoses from the PCV valve to the intake manifold. Pay special attention to the rubber elbows. They often crack on the inside curve and the crack is hard to see.

SOURCE: missing problem

300 and up engine misfired the spark is not going to the spark plug bad plug wire you first do a tune up 99% of time you gonna fix it good luck pierre

SOURCE: 96 Ford truck engine lIght will not go away.

this is the problem with code readers they bwill tell you the code and sometimes even have a reset feature. However they do not tell you the parameters and don't have an drivability feature so you can not test the ecm and all the sensors or modules while engine is running. diagnostic scan tools are very expensive and hard to use unless you have been trained to do so and PEP BOYs is not what I call real reliable mechanics to begin with. Now I concure with toddG on his reasoning in what might be the potential fault. if your vehicle is running rich or lean your O2 sensor will pick this up on the exaust side, however it is not the sole sensor responsible for the ecm adjusting the fuel air mixture.. you stated that you have switched out several o2 sensors and the fuel pressure regulator, but there is also you mass air flow sensor, your TPS sensor, as well as your map sensor these are worth checking out and just because a faulty sensor is the problem doesn't mean you will get a code each time. the system is built with redundancy in order to keep the vehicle running. in order to get the best possible diagnois take it to a shop where they have a full diagnostic scanner this will have not only OBD1 and OBD2 but cam protocol as well. while the tech is scanning the vehicle he will be able to see how the engine is performing under realtime conditions. please rate this as well as change the rating for toddg because he did offer a valid suggestion

SOURCE: Code #P0171 & code #P0174

The intake manifold gaskets need replacement as well as the o-rings inside - if you call FORD they should be able to get you the correct parts.

SOURCE: i have error codes p0156 p0161

  Check the wire harness near the top of the engine in the rear. They were good for rubbing through on the trans fill tube bracket. Judging by the code you have 4 sensors. you would be interested in the drivers side rear sensor.