got the code p0420 on my 02 f-150 4x4 with the 5.4l. the scanner that autozone has said that it is catalyst efficiency low bank 1. my question is wat is low bank 1 cuz the service manual dosnt say low bank 1 just bank one. i know theres a problem with one of the o2s i just dont know wat one to replace on that side. i had just put aftermarket cats on a month or two ago so it cant be them.

 

Want to bet?

 

Meaning Catalyst system efficiency is below threshold (Bank 1) There are sensors before and after the Catalytic. They are indicating the Catalyst isn't doing it's job. Check the Right side "Passenger side" Catalytic converter, make sure some didn't drill it and steal the catalyst beads. Look for plugged weep holes in the exhaust system, this is more of a problem during the winter, with short trips, than summer.

 

Discribe what cats were used and how the job was done.
It's still the cats you put in are not working well enough.
Using a Scanner to look at the action of the rear OX sensor compared to an assumed good rear side 2 would show the difference.
I just had the experience and see the PCM suspends looking at the rear sensors if one side is faulty for many drive cycles because the info signal is useless when there is a fault with the cats.
If a look shows no output they are suspended and would need to do a code clear to get the PCM to look at them again.
When you obtain an aftermarket 'assembly', be sure the rear OX sensor 'bung' is placed at the proper angle and not straight up like a major mfger is doing until they were told about it. Straight up, you can't get the OX sensor in without hitting the cab floor.
Do the right testing and you will see the cause of the 420 code.
Good luck.

 

well let me start from the begging. i put pacesetter long tube headers in and because they were much longer than the stock manifolds were i had to redo the rest of the exhaust. the old cats looked pretty weathered any ways. the headers had bungs in em all ready for the front ones so the exhaust shop had to install bugs for after the new cats since i was replacing all the exhaust from header back. now the front two o2s i had to lengthen a few inches do to the longer header. now i did go from 4 cats on the truck to 2 cats. dont thank that would matter would it? the cats i used were from a company call walker exhaust.

 

I'm not sure I understand what was lengthened on the front OX sensors.
If they are now out of the direct stream of gasses, it's a no no.
Next the rear sensors must be in the middle of the rear cats.
Unless the sensors can detect and report the proper signals as to how much oxygen is stored, the switch ratio that detects the operation of the cats will fail and set the 420 code.
Let me say something that has possibly never been said on this board.
Front OX sensor location:
They are right near the manifold/ head pipe locations for several reasons.
1. They get heated quickly.
2. The PCM can adjust fuel injection on an instant per cylinder basis which means the feed back from the OXs have a timed function.
3. The OX sensors have access to the all the cylinders gasses on each bank.
************************************************** ****
Once you begin to alter the physical demensions of the system with aftermarket hardware, you are violating these timed and temperature sampling engineered parameters.
The result is, expect it to work, not work, or not work very well.
.
Some other things to be awhere of is if the OX senors are to far away, the cats are to far away, there is to much exhaust gas cooling in the pipes extra distances. This make the cats and sensors too slow to react, not work at all or delayed working until higher rpm is dumping higher temp gasses into the longer system at a more rapid rate.
I have no idea what you will have to do but this is the baseline info you need to know.

BTW, your the second one to come and ask for help and not give the full details in the first post that misleads any attempt to help until later it come out of the closet and changes the whole picture.
Good luck.

 

lol sorry was just tryin to keep it quick and simple. i had to extend the wires for the o2 sensors before the cats cuz the original wire harness wernt long enough to reach its plug that it plugs into. the cats were welded right after the header then the second o2 was installed right after the cat. i had made these mods a couple months ago and im just now getin the check engine light. now when removing the o2 sensors the first time to install the headers i noticed all four of them were a little white but i was told that can also be cause from using injector cleaner. witch i have once.

 

You can't tell very much from sensor color just like plug color on these computer controlled engines.
Normally the exhaust will be on the lean side and tend to make visual signs whiteish.
It can be the additives in the fuel, your additives or just lean running.
It's more of a concern if they are blackish looking.
The important thing is the OX sensors detection of Oxygen content not any other part in the exhaust gas.
What you see is only on the protective shell of the sensor tip.
The way you would get a line on this is if the PCM tells you via Scanner that the Fuel Trims are about centered in both long term and short term fuel tables, then everything is as good as it can be reguardless of the color you see.
You are beginning to see how critical these systems are once you try to re-engineer them in the name of higher performance.
It take a good shop that knows all this to pull off a succesfull modification.
They would look at the parameters and see what results and make corrections as needed.