Hi everyone,

I recently finished up my Doug Thorley LT header install on my '06 V8. I didn't have the resources to buy a URD O2 Simulator, so I've been driving with the CEL on for Catalyst Efficiency (on both banks) for about a month now. Not exactly the most convenient to have to carry a code reader with me and constantly reset the codes when driving back and forth from college in the snow and ice so that I can have traction control.

With that being said, I just now started looking for an O2 Simulator from URD. When I couldn't find it on their website, I emailed support. This is the response I got:
"Due to EPA bullying of small businesses, we do not have such a product."

What are my options?

That's not bullying of small businesses, it's enforcing the law.

Not my words, just a quote from the support team's response.

So the new exhaust removes the cat so no change from upper o2 to lower o2? Someone on here has made a small cover that goes over the internal sensor o2 part to block off the holes. See below.

Say Hello to my Lil Friend

Digging around it looks like Duffdog is no longer making them.

Yup, fully understand. Just a little disappointing that a supposedly up and up business would blame government for holding them to uphold the law. Sounds like a bit of a cop out to me. Basically, they were selling an illegal product.

Very interesting, I know I’m in somewhat uncharted territory here, so bears with me. Does the long tube headers install have you remove the cats?

My past experience with LT headers is it pushes the O2 sensor back that it takes longer to heat up, causing these types of issues. There has got to be another way to trick the O2 sensor if the simulator isn’t available. Just brainstorming,Chip tuning if available might be one way, but expensive. Kinda wander if there is some sort of simulator on other Toyota vehicles use that might be readily available, thinking outside the box?


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When my cats started going bad I used the old downstream sensors and built my own dummies so my truck would run correctly until I had time to cut the chokers out and straight pipe it. If you're skilled with electrical all you have to do is wire the correct capacitor and resistor into the sensors wiring to relay the correct values to the ECM. RadioShack has them for a few dollars. Someone posted a schematic on how to make your own dummies on here somewhere. Easy to test your work with propane torch and multimeter. So if you f_ck up it won't matter much. I hope you plan on getting an a/f ratio tune to put that exhaust system to good use. After changing the way it breathes and exhales your a/f ratio won't be proper without a tune. This can actually cause your downstreams to set off a code also. Pollution comes from idiots that don't understand proper combustion. Basic organic chemistry. After a proper tune your truck will be more efficient than it was brand new with chokers. Not to mention the huge hp and torque gains. So how does it sound 🤤

The law's retarded and obviously not effective. The ozone layer has a giant hole in it. I think the law should put cats on trees and greenhouses too 😂 even the 9 billion humans mouths expelling the same products as fully combusted fuel 🤔
CxHx(fuel)+ O2(oxygen) → CO2(carbon dioxide) + H2O(water)

BOJACK 5X11mm 1uF 50V 1MFD 50Voltage +-20% Aluminum Electrolytic Capacitors(Pack of 10 Pcs): Amazon.com: Industrial & Scientific
E-Projects 10EP5121M00 1M Ohm Resistors, 1/2 W, 5% (Pack of 10): Amazon.com: Industrial & Scientific

Here is the rough drawing I found online and the resistor and capacitor I ordered to try it out this weekend.

@Jakeepoo3 ... is the 4th Gen 4Runner ECU programmable?

Yeah, the LT headers completely replace the stock manifolds (including the cats) and bolt straight to the y-pipe. I thought about welding cats into a DT y-pipe I purchased, replacing the resonators that come on it. I ended up not doing that (because I'm still waiting on my y-pipe after a few months) and deciding to go catless instead.

I'm completely new to this, but I have been considering an A/F tune for my 4R. I have no idea how to go about it though-- I'm not sure if I'd need a piggyback or some kind of chip, or if I could just throw my truck to a tune shop and call it a day. How would I go about this?

Here's how it sounds (super sexy imo):
https://i.imgur.com/CFcTXaL.mp4
https://i.imgur.com/Oe72qTZ.mp4

Yes sir that's the same setup I used. Tips from experience. Weather proof your work with marine quality heat shrink sheathing. Don't mix up the right and left connector. Make sure they go back on the same side. Check out unichip and underdog racing. Yes it can be flashed. The results will be better and probably cheaper than using a Dyno tuning shop due to the fact you're actually tuning it in real driving conditions.

Definitely need a a/f tune. It depends on you really because it's a pretty in depth subject with a lot of varying factors involved. I prefer diy tuning in real driving conditions. Check out underdog racing or unichip I believe they offer 4th gen ecu reflash and tuning products designed specifically to fool your 4runner ecu. I would advise against those performance chips there are way too many factors and variables involved that aren't considered by a chip. Get ready to double your hp and torque gains!

Hey, please keep me updated on how it turns out! Is there a writeup that you've decided to follow?

When you say 'diy tune' I imagine some guy in a street race-esque early 90's Civic with a laptop going 200 down the interstate haha. What exactly does it look like to diy tune a 4runner? I'm almost certain I don't have the expertise or knowledge to pull something like that off.