The codes indicate the circuit that needs to be diagnosed. After the diagnosis is when a part is replaced if that's what's needed. You're replacing parts before the cause of the problem is diagnosed. That's the most expensive and least effective way to fix a problem.
The oxygen sensor codes could mean that side of the engine is running lean. You don't replace the sensor just because you don't like the problem it reported. One thing to keep in mind is when you have a misfire it is due to loss of fuel, loss of spark, or loss of compression meaning an engine problem. The most common cause is loss of spark. That means unburned fuel and air go into the exhaust system where the oxygen sensor detects the unburned oxygen. You might smell the unburned fuel at the tail pipe but oxygen sensors don't detect fuel, just oxygen. Depending on the strategy of the Engine Computer, it might command more fuel to that side of the engine in response to thinking it's running lean. That will make your fuel mileage and engine performance even worse, and no matter how much extra fuel it adds, there will still always be that unburned oxygen getting detected.
Another common problem that only occurs on Ford trucks is a plugged EGR emissions tube. The passages become plugged with carbon. If the passage to one cylinder is plugged, only fresh air and fuel will go into that cylinder and it will be fine. As more and more passages to different cylinders become plugged, pretty soon all the exhaust gas is routed to the one remaining cylinder where its passage isn't plugged yet, and since there's so much exhaust gas going into it, there's no room for fresh air so that cylinder misfires. As far as the EGR tubes are concerned, the one going to the misfiring cylinder is the only one that isn't plugged.
Those are just a couple of examples of what can happen. As I mentioned previously, wiring problems are just as common as sensor problems. A bad sensor will be the cause of setting a fault code only about half of the time. Their purpose is to monitor specific aspects of the engine, and when they set a code because something is wrong with the way the engine is running, they're doing their job. Replacing them isn't going to help.
Sunday, August 19th, 2012 AT 12:57 AM