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P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Indicates Bank 1 catalyst system efficiency is below the acceptable threshold Use of leaded fuel
Damaged HO2S
Malfunctioning ECT
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires improperly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Compare HO2S upstream and downstream switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.

i dont know what to say buddy.
 

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I seek the knowledge of the gods of the pantheon known as Focaljet.

I keep getting a cel with a code of P0420. My mods (or at least the ones that could cause the problem) are: Volant, BBK tb, Edelbrock header, Random, Bosal flex, Borla exhaust.

I first got the cel after installing the header and I figured I fried the stock cat. So I installed the Random & Bosal and also replaced both O2 sensors and a damaged EGR tube. I then noticed a cracked weld on my header so I replaced that this past weekend. Everything is tight & complete yet I still get a code P0420 which comes back w/in 100 miles of clearing it. I drove around for a while with a leaking EGR system and then again with a cracked header. Is it possible that the new O2 sensors went bad because of this? I really don't know what to do next. Please help.
 

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P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Indicates Bank 1 catalyst system efficiency is below the acceptable threshold Use of leaded fuel
Damaged HO2S
Malfunctioning ECT
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires improperly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Compare HO2S upstream and downstream switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.

i dont know what to say buddy.
Yeah, thanks. I got that far too but now I'm stumped
 

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It's possible the original cat failed, then the Random tech cat is not efficient enough for the Focus' system. If you have the ability, monitor the switching of the o2 sensors and see what they're doing.
 

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It's possible the original cat failed, then the Random tech cat is not efficient enough for the Focus' system. If you have the ability, monitor the switching of the o2 sensors and see what they're doing.
Can this be done with a multimeter? and if so what would I test for? Also, it crossed my mind, what you said about the Random cat. However alot of jetters have 'em and I don't recall anyone throwing a cel because of it.
 

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i've done the samethings that you did all of it man i just don't know what the deal is.. i think its something about where the second o2 sensor is located.. i'm getting a scan tool just to keep with me so i can turn the engine light off it pi*ses me off..
 

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I've got the scan tool already but I've got to turn the damn thing off every other day
I'm guessing I should try an O2 cheater?
 

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You can try using a meter, but it will just bounce all over the place. Check it with a scan tool, but I would think the only other way to keep everything You have and not have a MIL, would be to get a MIL eliminator.
 

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yes MIL=Malfunction Indicator Lamp
 

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odd that he would trip the light when many others run a random w/o a light (myself included for a long time). hell it takes a wk for it to come on w/an orp.

-Ult
 

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I have the Random and had the same issue with the cell. Installed an O2 cheater and the problem was solved.

George
 

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Ult, I thought the same thing as you until I read JPulido's post (thanks) I guess I'll try an O2 cheater. McNews carries them heyna?
 
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