What is a defouler?

[A970747]

Hi all,

I'm wondering if you technically savvy people here could answer my questions about what a defouler is, why you would need them. I have an 08 civic Si!

Thanks!!

(P.S. FA5 = Sedan, and FG2=Coupe?)

[chrisfrofro]

its basically your O2 censor simulator.. people typically use a "defouler" with a raceheader as to not throw a CEL

[NitrousG35]

I found a fantastic article about this on a BMW website: solution: Check engine light w/ aftermarket Headers - E46Fanatics

Headers and/or Cats: Catalytic Inefficiency solved


WHO: People who upgraded to aftermarket headers without installing any catalytic converter will get a catalytic inefficiency error code. Likewise, people who install high-flow catalytic converter will get the same "inefficiency" error codes.

WHAT: Catalytic Inefficiency codes on the post cat 0xygen sensor: P0420 (cylinder 1-3) P0422 (cylinder 4-6).
Ref: http://www.obd-codes.com/trouble_cod...old-bank-1.php

WHY: The reason why your OBD-II diagnostic systems report this error code is because the 02 sensors detect an above normal exhaust reading when compare to OEM catalytic converter. The OEM catalytic converter does an excellent job at filtering/cleaning/converting exhaust fumes into cleaner air. The DME/ECU calibrates its post-cat sensors to the OEM catalytic converter performance and specs. Therefore, aftermarket cats do not clean well enough to satisfy the catalytic efficiency monitoring of the DME. This is a very common problem with aftermarket cats especially the high-flow ones.
An "inefficiency" reading does not mean that your catalytic converter is broken especially if it is brand new. Again, the error codes just means that they are not performing as efficient enough to meet OEM standards.

SOLUTION: There are three feasible options to solve this inefficiency problem

Ignore.
Spark Plug non-fouler (aka Spark Plug defouler)
Software upgrade

-Ignore-Since the post catalytic converter oxygen sensors is purely for emission monitoring it does not in ANY way affect your fuel trim and car performance. Therefore, it is perfectly fine to ignore the check engine light.
-PRO: No time and resources wasted on fixing problem
-CON: Annoying check engine light

-Software Upgrade-Software upgrade from major tuning companies will flash your DME to remove the "catalytic efficiency" monitoring feature.
-PRO: Fast and requires no hardware/equipment modification to exhaust systems
-CON: Expensive

-Spark Plug non-fouler (aka Spark Plug defouler)-By installing the spark plug non-fouler, you are in essence moving the rear 02 sensor out of the direct flow of the exhaust stream/flow. By doing so, you are tricking the 02 sensor will an inaccurate reading. Since the 02 sensors is not directly in the path of the exhaust fumes, it can not accurate measure the exhaust fumes.
-PRO- Inexpensive
-CON- None

[A970747]

Thanks, that answers my question fully!!

[e60.deluxe]

why isnt illegal in any of the cons?

[bigmsi]

Will the defouler work with a header with cat-delete.

[bigmsi]

if yes? what store sale's them.

[Kidekat]

I don't see why people pollute the environment for a few hp? Our cars make over 350hp with a high flow catalytic converter that was able to pass California's New Smog II standards.

[chrisfrofro]

Originally Posted by bigmsi

if yes? what store sale's them.

read here:

so now that strutking doesnt sell the defoulers anymore...

[portabuddy]

i got mine from parts source...


and here it is a year later...

[furryferret7888]

Originally Posted by e60.deluxe

why isnt illegal in any of the cons?

because its not illegal in some states...like mine...no emmission testing anwhere....