My wifes need to be replaced. Is there 4 total ?? I am looking at the all data pro shop manuals and I see 2 that say "Catalyst monitor sensor" and I see 1 that says "Heated oxygen sensor" . Are these the o2 sensors ??? I am only seeing 3 total though.

 

I'm just shooting from the hip, because I haven't seen your car....There should be 2 upstream of the cat. About even with the spark plugs that are closest to the firewall on both sides. Sometimes these will be heated (a third, or fourth wire running to them to get them up to temp the first few seconds of running). These are the ones that typically get replaced because they have an effect on performance. Now if you have 2 cats, or just one depending on dual or single exhaust, each cat will have 1 about a foot after it. These do nothing for performance and should last the life of the vehicle.
Why do you think yours needs to be replaced? Codes, broken, or ???

 

My wife called and told me her check engine light is on and the car is reving up and down when she is at a redlight. It has 90,000 miles on it so I am just asumming that is the problem. I'll know more when I get home and can get the codes.

Its a single exhaust out the back but it looks like there are 2 cats before the muffler. The 2 exhaust pipes (with the cats) go into one muffler and after the muffler it is just one exhaust

 

Just ran the cpu and it said the #1 O2 sensor in bank 1 and bank 2 is stuck lean. So, should I just change those 2 or all 4 ???

 

Don't change any of them. Start looking for vacuum leaks. If you've got one of those two letter cotton oil gauze million mile red air filters, inspect the mass air sensor heated wire for any contamination from the filter's oil. Inspect the PCV tubing closely for any signs of deterioration or leaks.

I really, really, really, really wish people would quit flinging O2 sensors at a vehicle, hoping for a fix. O2 sensors are tattletells. The only time they really fail is when the heater element fails or they start switching slowly/not at all.

When you start getting upstream lean codes, especially on both banks, you need to start looking for unmetered air entering the engine after the mass air sensor before anything else. The most common place is somewhere in the PCV tube assembly, between the passenger's side valve cover and the intake manifold. Inspect this tube very closely, especially at the rubber 90 degree elbows where two hard plastic lines join together.

Is this thing running or idling rough? Stalling?

 

It has 90,000 miles on it so I would assume they need changing??? I thought they only last for a certain amount of miles. It's idling rough.

 

Depending on who you ask, O2 sensors can last 30,000 miles or 300,000 miles. The performance minded folk seem to think that a typical O2 sensor loses a lot of its efficency at around 30-50K miles; I've still got the original O2s in a '97 F250 with 179K miles. I don't especially ask a lot of an O2 sensor, as long as the heater is still working and it's switching properly, and I don't have more than a 10% correction either way on long term fuel trims, I'm happy.

Remember too, that O2 sensors have no direct effect on idle quality. So if the engine is running rough, stalling, etc., more than likely it's not an O2 sensor concern. Yes, the O2s can affect air/fuel ratio, but if a fault is detected, the PCM will go into open loop - ignoring any inputs from the O2 sensors - long before a faulty O2 can affect the air/fuel ratio enough to cause running problems.

With 90K miles, take a good hard look at all the hoses in the PCV system. You may be able to hear a hissing noise from a vacuum leak in one of these hoses with the engine at idle.

 

okay, Thanks. I'll check all the hoses too.

 

I agree with Quintin. In fact, do not change your sensors until you have the problem fixed. Then, fix 1 thing at a time, so you know what you just did if it doesn't run correctly afterwards.

 

I could not find any vacuum leaks. I replaced the 2 o2 sensors and the CEL went off and no codes came up. Then, I got p2195 and p2197 after a few minutes (sensor stuck lean)...............any ideas on what it could be. Could it be something as simple as a Throttle Body adjustment ????? The CEL is not on and it is still idling rough. About every 15-20 seconds the rpms will drop down and that is when it idles rough.

I disconnected the batter for 20 minutes to reset the computer too.

 

Sure still sounds like the symptoms of a vac leak. Check for leaks with carb spray.

 

It is. Guess it helps when you look during day light. I found the leak, thank God. I'm not sure what the part is called though. It's a "L" shaped tube that appears to go into the back of the throttle body. It has a hole in it. ANy idea what this part is called ??? I put the old O2 senors back on and took the new ones back so I'm good there. And I learned something too in the process.

 

The tube you need is part of the PCV valve assembly. At the dealer, it's serviced as a complete assembly, with all the connectors and a new PCV valve. There should be a black and white tag somewhere on it with an old part number that a dealership parts department can use to cross over to the correct service part.

 

I had to order the hose from Ford. Auto parts store didn't carry it and Ford didn't have one either. It was $20. Is the old hose hard to take out (does it just pull out) ? I am talking about where it goes into the back of the throttle body.

 

Yeah, it's just a press fit into place. You may have to use a flat blade screwdriver or something to get it started coming off the fitting.