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Old 07-08-2007, 01:31 PM   #1
Deep Blue
Join Date: Jun 2007
Location: Bay Area California
Posts: 451
My Ride: M52TUB28
solution: Check engine light w/ aftermarket Headers

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).

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
  1. Ignore.
  2. Spark Plug non-fouler (aka Spark Plug defouler)
  3. 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


People aftermarket headers w/o cats

Go to Autozone and buy a pair of 18mm long and short "Spark Plug Non-Fouler."
Brand: HELP!
Part Number: 42009 (short) and 42002 (long)
Price: $3.50 for 42009 and $3.50 for 42002

Modify the short spark plug non-fouler (P/N 42009) to make the hole bigger in order for the oxygen's sensor tip to fit comfortable inside the spark plug non-fouler

Install your 02 sensors as followed:
O2 sensor, modified short fouler, long short fouler.

You are using two non-fouler to increase the distant between the exhaust fumes and the 02 sensors.

People with aftermarket headers and cats

Since you already have cats, you don't need to move the oxygen sensor out of the direct exhaust fumes as much as the people without cats.

Go to Autozone and buy a pair of 18mm long "Spark Plug Non-Fouler."
Brand: HELP!
Part Number: 42002 (long)
Prce: $3.50

NOTE: The package only comes with 2 non-fouler. In the picture above, there are 3non-fouler as reference only to help illustrate what a non-fouler looks like from different perspectives

Install your 02 sensors as followed:
O2 sensor, long short fouler.

NOTE: You might need to modify the long spark plug non-fouler (P/N 42002) if your 02 sensor's tip doesn't sit properly inside the spark plug non-fouler.

The oxygen sensor shown in picture is a pre-cat and NOT a post-cat. Only used as reference to help illustrate installing the non-fouler into the sensor.

When installing cats, you do not need to extend your o2 sensor. Simply re-wire the 02 sensor wire harness inside the engine comparment. This will give you an additional 3-4 feet of wire.

I hope this helps. Post your questions here if you have any. I am willing to help any fanatics with this modifications via online or in person for free.

Last edited by Deep Blue; 07-08-2007 at 01:41 PM.
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