THE SKINNY:

Just installed a new Megan Racing Header (which is only available as a cat deleted system) and the upstream O2 Sensor port is too close to the Heat Shield / Tunnel to allow for an O2 Sensor to be installed (even if I had installed the sensor before mounting the header).

Let me first say, I am not expecting to just remove the sensor and go on my merry way.

I have read a number of threads and I have a pretty good idea of how O2 sensors COULD reasonably work in conjuction with the ECU. ( I am a mechanical engineer (with a 4 year degree) and former aircraft mechanic with a 2 year degree as CNC machinist, but I am not by any means an expert on modern ECUs) What I don't know is how the ECU ACTUALLY utilizes the data from the O2 sensors in this application.



WHAT I WOULD LIKE TO DO:

Install an 02 Sensor harness extension (or just extend the harness) and put the upstream sensor in the downstream bung (readings should be the same as there is no cat) with an O2 sensor simulator for the actual downstream sensor.



WHAT I DON'T KNOW

If I install an O2 sensor simulator, how does that work with the computer? Is it essentially creating a stand alone signal (like for example just playing a recording on a loop) that simulates an "acceptable signal". If this is the case, shouldn't I assume that a B.S. signal will cause the engine to run at less the peak performance. For example if the engine should be creating "X" amount of O2, but is actually creating "Y" amount, the ECU wont correct the mixture if the simulator keeps telling the computer that it is reading "X" amount of O2. Does that make sense?

Or does the O2 sensor simulator take a reading from the upstream sensor and modify it to read the correct theoretical O2 reading given a functioning cat?
If that is the case, wouldn't the simulator need to tap into the upstream sensor signal as well as be plugged into the downstream sensor plug.

Or.. Does the computer not use the down stream sensor for adjusting/calibrating fuel map? That is to say, the downstream signal is only used to throw a code (that doesn't affect the fuel map / timing) when the O2 levels deviate from acceptable emissions standards if for example the cat isn't functioning properly or is removed.



ALL OF THAT BEING SAID:

Will what I am suggesting work, and if so, which O2 simulator should I use? I can only find one, but I am not sure if others exist.

O2 Simulator from Way Motor Works
waymotorworks.com/o2-sensor-module.html
Not sure how this installs as it appears to be nothing more than a pig tail with a plug at one end (that I assume plugs into the stock downstream connector) and three unterminated wires at the other end that I assume need to be wired to something, but I have no idea how/where they need to be wired.


I realize this has been a small novel and I really appreciate it if you have made it this far. I could use any help or guidance I can get, I am not sure where to go from here. Really, any advice would be hugely appreciated. Thanks again!
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The first o2 sensor does most of the work for the ECU. This sensor adjust the fuel trims, tells the computer wether your running rich or lean, if there is an exhaust leak, and give information for the 2nd o2 sensor to work with. This 1st sensor should not be altered in anyway unless you have a standalone ECU and are willing to change your car's tune with the weather.


the 2nd o2 sensor takes the information from the 1st as in a resistance (to show exhaust temp). the 2nd o2 sensor also has a resistance (to show temp) if temp from sensor 2 is higher than temp from sensor 1, it knows you have a cat in place. this is all the sensor 2 really does. most people who go catless use the thing you listed above from way, or pull that sensor out of stream so it doesn't throw a code. your problem is the 1st sensor is in the way of the heatshield.


there is a few ways of doing this. (granted this is the first time im seeing this problem) You could push the heat shield in to make the room. OR get a bolt, plug that hole, and somewhere else close to that spot where all 4 streams are collecting and add a new bung in a location that the o2 sensor will fit.


the o2 sensors are always sending information to the ECU except when they are under temp. which is immediate cold start up. but they warm up quickly

 

An important note...
The upstream and down stream sensors are both the same type..meaning NEITHER is a "wideband" type...(most cars of this era use a wideband sensor in the upstream)...
Since the sensors are pretty dumb, and slow reacting, you could try doing what you propose... Might work...
Many folks have welded the stock cat to a header, like the RMW shorty, and have ZERO issues making 250+ HP...so maybe it might be worth selling what you have, and buying a better suited header...
As a pilot, I greatly respect any AP mechanic (have spent many hours with many), but sometimes, saving $100 is not with the issues (buying more parts to "make it work", MAYBE, like o2 Sims, bungs, etc, then the time)... Like I said a RMW shorty with a stock cat is a good combo, makes nice sound and power, lasts a long time, and is emissions, and inspection legal, no lights.

 

I have the same header and I can tell you what I did. I took the header to an exhaust shop and had them weld a bung where the 4 pipes meet and go to 1. I did it on the same side the the stock bung was on (I believe it was driver?) There was enough clearance up there for the sensor and was close enough to plug back in. I did this because I did not want to extend and o2 sensor wires. The header will have to be out for this to do this though.