My truck is a 1997 F150 4.6L RWD with approx 150k miles.

Recently I received an error code related to the O2 sensors (I wrote it down and cleared it and then foolishly lost the paper). It indicated a

problem with the catalysts.

I cracked my ribs a few weeks ago and was forced by my wife to take the truck somewhere rather than looking it over myself. "Your doctor told

you to take it easy" she said. I had a coupon for 15% of a repair service at the PepBoys so i dropped it off there. They cleared the code and

called to tell me i need all new Cats. $1800 and they were pretty sure it would be OK.

No thanks. I picked it back up a day later and took it to a muffler shop. I told them my story and asked to took around for leaks and see what

their opinion was on the condition of the cats. They called back and said from the outside it was a little rusty but otherwise looked OK.

They recommended a tune up rather than new cats. I agreed to new plugs, wires, and a fuel filter change. They were all over due so I didn't

have a problem with the idea of replacing them. They used motorcraft parts and cleared the code.

Two days later the light was on again. Idle is rough. I hooked up the code reader and captured P0174 System Too Lean Bank 2. I cleared it.

Then I got it up to normal operating temp and decided to monitor the O2 sensors in action. Bank 1 sensor 1 and bank 2 sensor 1 look pretty good... they are very similar. Bank 1 sensor 1 looks a little more rounded and slow compared to Bank 2 Sensor 1.

Here is the graphs: http://imgur.com/a/IOwfZ

The part i am unsure about is Sensor 2. I assume this should be a relatively smooth graph if the catalyst is doing its job correctly. Bank 2 sensor 2 is almost always a smooth line. At idle, 1500rpm, and 2500rpm it looks like a smooth line. However, Bank 1 sensor 2 is all over the place at 1500rpm and 2500rpm. I don't know which behavior is normal. I am also not sure what this means.

I was thinking of letting it cool off and then swapping the two sensors in position 2. I would like to see if the readings are the same. then i would know it is not a sensor issue. I could narrow it down to maybe a catalyst problem or a combustion problem (maybe clogged injector?).

Any thoughts on how i should troublehsoot this problem?

 

P0174 has nothing to do with the down stream HO2S. It trips when the sum of STFT + the LTFT exceeds ~32%. It is usually a vacuum leak, especially since you do not also have a P0171. Have you checked the infamous PCV rubber elbow behind the intake manifold. Prolly have to go by feel to find it.

Your B2S2 is more normal. If the PCM objects to the signal from your B1S2 you would get the dreaded P0420.

 

As soon as i read your reply and the P0420 comment i realized that is the code i got originally and wrote down and then forgot.

I will need to put some more miles on it and see if that code comes back.

Where is the infamous PVC rubber elbow that you are talking about? Do you have a diagram or a link to another post i could view so i know what to look for?

Thanks for your reply.

 

Here's a picture of one that I googled for you:


Its for a F150 but it should give you the idea of what your looking for.

 

Lets come in, out of the rain! You got to many opinions and don't want to believe the worst of it.
You here to get the truth.
.
You must go by the codes you get.
You have 2 problems.
The 420 code is a bad cat on bank 1 passenger side.
If you have a 430 it is bank 2, driver side.
You have no choice but to replace cats on the side matching the 4xx code.
You may or may not need new Ox sensors depending on what happened.
If there was a misfire that caused the cat to melt, new sensors are needed because they are likely also melted..
Aftermarket cats for the right side are in the $300 range plus installation and any other materials.
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The second issue is an air leak in the intake tract for the codes 171/174.
Look at all hoses and fittings.
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You have to service for these codes. Clearing them does not fix anything.
Sorry you have this issue with the cats.
Good luck.