So first of all, before yellin at me for not searching, I had a hard time because the search conveniently leaves out 02 when searching for "02 sensor wiring"
Vehicle: 96 f150 4.9L 133k miles
my first question is, which of the 4 wires is the signal wire for the 02 sensor, theres a black, 2 whites and a grey.
2nd. is there a trick to getting the upper 02 sensor off.

The reason I'm asking this, is my truck has been throwing code P0420 since January, I'll go reset it and it'll come back after a few weeks. I know that the code is catalyst system efficiency below threshold. I'm leaning towards it being the catalytic converter, as the truck runs fairly smoothly, with the exception of only getting about 10-11 mpg in the city. I had it all tuned up, and all fluids flushed and replaced last November when I bought it, it passed emissions first time easy, in November, which confused me, as I thought if the cat was going out, then it would have a harder time passing emissions..

So I'm planning on testing my 02 sensors, and if their bad, replacing them. and then moving to the catalytic converters/exhaust system.
Basically what is the best way of replacing the cats (or exhaust system) for a relatively stock system, but I wouldn't mind a bit more power if it came along with it...
If I were to get a single cat, like the magnaflow, or catco, or other brand that is better? Should I just get a full catback exhaust system (kit) to go from there back? Or just cut out the cats, replace, then straight pipe to a muffler, and tailpipes?
I'm not looking to drop a ton of money into it, (but at the same time, I do understand, that exhaust systems are not cheap)
What would be the best fix, i.e. replacing just the cats, leave everything else, replace the cats with single, and then aftermarket muffler? that would fix the error code P0420 (assuming it's not just the 02 sensors)

The other thing, that seems to potentially cause the error P0420 is the ECT, but it has no symptoms starting, or running at all, other than the bad mileage, and wouldn't this likely trigger another error code as well?

Thanks,
Erik

 

The bad mileage could be the result of the ECT sensor sending the wrong temperature signal, as in too cold. The PCM would be dumping in more fuel. Too much fuel in turn can contaminate the converter(s). It's a chain reaction.

I do not have a color code listing for the O2 sensor lead itself. This diagram might help: Ford Fuel Injection Oxygen Sensor (HEGO)

Magnaflow has a decent replacement front pipe/converter. From there it is a matter of choice of which muffler you want depending on the sound qualities you are looking for. Sometimes finding converters for '96 models is difficult because of the front and rear O2 sensors.

 

Well, that seems like it might be something worth replacing regardless...
It's only a $16 part at autozone and I have a $20 credit there for spending $100 last time.... Is the duralast brand good enough quality for this part? or is it typically preferred to stick to motorcraft?

 

It's free to check it with a volt/ohm meter. Here are the values: Ford Fuel Injection Engine Coolant Temperature Sensor (ECT)

I would shy away from an aftermarket ECT sensor. Just my personal preference.

 

How do I know what exact temperature the engine is at in order to check the voltages and resistances?
Thanks

 

I know several people have removed the ECT then placed it in an oven of a known temperature. Start off with the ECT at room temperature, take a reading (ohms). Then place it in an oven around ~250 degrees for 10-15 minutes, use an oven mitt to remove it, then carefully measure it again. Many ovens also have a Proof setting (~115) and a warm setting (~160). That way you can plot the resistances to see if it matches the values listed in the chart from the link I sent earlier. If you really want to plot it accurately you can also stick it in the freezer.

That should give you time to have a beer or three in the name of science.

Of course I suggest this because I am a really cheap bas***d and hate to spend money if I don't have to. Too many times I have replaced something only to have it fail a short time later. I want to make darn sure I am not chasing my tail.