01 Expo with Engine code P0420

[s.mac22]

This may be a bit lengthy to make sure I add all relevant information.

My Expedition is '01, 4.6L, 188k miles. I had a previous code (I think it was P0360), that stated #6 cylinder was not firing. Since, I have replaced all the plugs/w Autolite double platinum plugs, the boots, and a new coil for #6 cylinder. There was an immediate improvement in performance and operation of the engine.

I drove for two days under normally sedate conditions, i.e., smooth, casual takeoffs, no heavy acceleration or agressive driving. During the second day I had to 'get-on-it' to merge into freeway traffic, which caused the 'Check Engine' light to come on and stay on. No flashing, no intermittent, just on, all the time now.

The operation seems to be 'normal' to me but I can't really guage because I have only had the truck for 2 1/2 months now.

I disconnected the battery, hoping for no code, but still have it. I got the code read at local A-Z parts store, and this is the code description:

Code P0420
definition- catalyst effenciency low bank 1

explanation- the oxygen sensors monitor the catalytic converters ability to store oxygen

probable cause- catalytic converter defective (failure possibly due to #2, #3, or #4)

2 -engine misfire or running condition
3 -large vaccum leak
4 -engine oil leakage into exhaust valve guide seals, piston rings

During this time of acquiring the truck through to this problem, I've noticed white smoke from the exhaust. I passed it as just running cold until warmup until I noticed that I was still emitting a little white smoke after driving for awhile. Also, after sitting with the truck idling for roughly five minutes, I got a lot of white smoke coming from the exhaust while driving for about 500ft.
I can't say that it does it all the time but it does it enough for me to know its a problem.

After reading the previous thread on the p0420 code, it seems apparant that I may have bad valve seals, or worse, bad rings.

I can tackle the valve seals with no problem. The rings though, not looking forward to it! The last time I did a rebuild was well over 15 years ago on a Detroit Diesel! Oh yeah, and 2 years ago on my Kawasaki ZX11!

As far as possible vaccum leak, does anyone have a vaccum schematic handy so I can check all the hoses?

Thanks for bearing with the long post.

Any expert opinions or advice?

Thanks,
Silas

[s.mac22]

No one has any input on this??? I havn't done anything but I am ready to tear into the motor now, so...heeeeeeelp!!

[Franco2112]

Have you ever changed the pcv valve? If not at 188k change it . You will see immediate performance. Just my take.
Franco

[s.mac22]

I actually did just change the pcv valve a hour ago but still have the CEL on.

[Davescort97]

Code 420 is triggered when the downstream HO2 sensor has fluctuating readings. Normally the upstream sensor has fluctuating readings and the downsteam sensor has a steady reading indicating the catalytic converter is doing it's job.

Some causes could be exhaust leaks around the converter, ignition timing retarded too much, a faulty HO2 heated downstream oxygen sensor, a worn out converter, or a plugged up converter.

You can check for a plugged converter by putting a vacuum gauge on a vacuum source and taking the reading. If it is less than 18 inches the cat is plugged and will have to be replaced.

[mrd2001]

White smoke usually indicates the a internal coolant leak, Possible head gasket leak could create some of your conditions. I don't know for sure if the coolant travaling through the convertor could trigger that code. Just something to think about.