A big thanks to mrfred, JustDSM, and bez for their insights on this.

For those of you who run catless, or prefer to use a wideband O2 sensor in the bung originally intended for the stock rear O2 sensor, here's a way to safely remove the O2 sensor without resulting in a check engine/service engine light (trouble code).

Step 1
Unscrew and unplug your rear O2 sensor. Completely remove it from the vehicle.

Step 2
Disable the Rear O2 routine in the ROM

• Update the ECUFlash XML file located at: C:\Program Files\OpenECU\EcuFlash\rommetadata\mitsubishi\evo\ 88590015.xml
  using FrontPage or other XML editor to include the following entry so the code ends like this:
  <table name="ECU Periphery0" category="Misc" address="faa" type="1D" level="1" scaling="Hex16"/>
  </rom>
• Open ECUFlash v1.3 and version 15 ROM image. Scroll down to the Misc section and locate the "ECU Periphery0" entry.
• If the value for this entry is "0x56DA," press "=" on your keyboard and type "0x56D8" (without quotes) and press Enter. If the value for this entry is "0x56DB," press "=" on your keyboard and type "0x56D9" (without quotes) and press Enter.
• Save the ROM image and flash your ECU with the new file.

Step 3
Simulate the O2 heater

• Locate the stock rear O2 electrical plug under the passenger seat, and find the O2 heater wires (red with a yellow tracer, and blue with a yellow tracer as seen below)
• Using a 10kohm/.25 amp resistor (found at RadioShack for $3..pack of 10), jump the heater wires creating a 10kohm resistance between them. You may find it useful to trim the resistor leads so that it fits down into the plug snugly.
• Use a ziptie to secure the resistor onto/into the plug.

**A ROM-based heater disable method may be identified in the future which will remove the need for the hardware simulation described in Step 3. Until then, this is the best solution that I've found.**

All done! Enjoy.

**Update**
mrfred has posted an updated version of the software patch for ver 15 IX ROMs here and l2r99gst has posted the simulation patch for version 96940011 (2005) here. These patches, and patches for other ROM versions, are available as part of the tephra mod patches as well.

**Update**
Some have reported difficulty getting the aforementioned resistor setup working properly without a CEL and without generating too much heat. This ECU circuit requires an ohm load between 1.1 and 80 to keep the CEL from coming on (thanks mrfred!). The configuration you see below should work well to keep within the proper parameters and keep heat to a minimum.

 

does this work for VIII's too?

 

Yes, this will work for the 8's, too. But, the OBD tests for the cat will never complete, so you will fail emissions. This will eliminate the rear 02 CEL though, if that's all that you're after.


Eric

 

This is posted for informational and race use only, right?

Don't want anyone sentenced for for being part of the natural carbon cycle.

Seriously - Nice rig

 

If you have a xede /w smart, the knock box has a front o2 sim built in so no need to do any of this for the 8 just wire in the o2 harness to the box and your set!!


for all the xede haters

 

So pretty much this is a o2 simulator type method.

 

Sort of....

It's an O2 CEL elimination method, and a heater circuit simulator (which prevents the rear O2 heater CEL).

 

I like the idea, hopefully creating a simple "only-ECUFlash" based code without the need of a mechanical 'fix' will be out soon!

 

It's in the works. when you have your car in for an emmisions check, the ODB systems look for 2 parameters. there is a set condition that turns on the check engine light, and a second parameter which is the readiness code.

this patch currently disables the CEL, but also prevents the readiness code from being set. Without this, you will not pass emmissions.

 

This works on all VIII roms that I have checked as well. They are all at the same address and start with the initial hex being the same (56da).

 

Is there a way to eliminate the rear 02 sensor, but still make it pass the readiness check for inspection? Or do you think there may be in the future with further coding?

 

There isn't yet, but there will be in the future. The ram address for the readiness test just needs to be found.


Eric

 

I have one of those narrowband simulators wired to the plug. Will that pass a computer emissions check?

 

man so close, i am up for emissions testing now, I guess i will just try the mechanical fix and hope i pass.

Anybody tried passing emissions with a test pipe?

 

good luck...