Hello --

I have a WORKS HFC that I want to install on my Evo IX. To keep things simple, I want to have an O2 bung welded onto it before I install it. Since I haven't removed the stock cat yet, I have two questions I was hoping for help with:

1) Are O2 bungs available anywhere (i.e. will most muffler shops carry them?) If not, where can I buy one? Autozone, online merchant, ?

2) I've attached a few pictures of my HFC. If possible, can someone let me know where on the HFC the bung should be welded? Ideally, please draw an arrow or make an "x" in Photoshop on one of the pictures.





Thanks for your help I know, I know... I should have had WORKS weld on a bung when I ordered it
RedAustinIX

 

Look friend, DO NOT have an O2 bung installed on your catalytic convertor, be it high flow, or not!

Is this additional bung for a wideband A/F ratio gauge? In any case, I think that the correct location for the install is on the downpipe a few inches from where it mates to the cat. The bung should be oriented somewhere between the 10 o'clock and 2 o'clock positions.

I think that Buschur Racing sells O2 sensor bungs. If not, then AEM should have them listed on their website.

 

With my IX, both of the aftermarket exhausts that I have had on my car have already had an O2 bung welded in the exhaust just AFTER it connects to the catalyst.

If this is for a wideband O2, then you would want it welded in the downpipe before the HFC. It it's for the stock second O2 sensor you'd want it after the HFC. Because the stock IX catalyst has an indentation to allow the stock O2 sensor to clear, I think your best bet is to...

1.) See if whatever aftermarket exhaust you are going to or will purchase already will have the O2 bung in it.

OR

2.) If you're still using the stock exhaust or your exhaust doesn't have the O2 bung in it, test fit everything and then mark a location on the side of the exhaust opposite from the drive shaft so the O2 bung will be in a nice horizontal position to clear the bottom of the car. Then have a shop weld one in the exhaust just after the cat for you.

 

sparky, Redv - thanks for your comments

Yes, the O2 bung is for the second stock O2 sensor. I guess I have a couple more questions now...

1) What is the reason that you're not recommending putting the O2 bung in the cat? Is it because I'm more likely to get CEL errors due to the "less-restrictive" cat and the sensor's extra distance from the cat helps?

2) Or, Redv mentioned an indentation in the stock cat. It sounds like HFCs don't have that -- are there clearance issues that prevent the O2 bung+sensor from fitting in the "stock" location?

Thanks again for your help!
RedAustinIX

 

Look, the location of the Cat is about ideal distance-wise from the turbine exducer. And if you had a Test Pipe or a gutted cat in that location, I would say locate your O2 sensor there.

However, since you are getting a HFC in the first place instead of a test pipe, I assume that you are a law abiding citizen trying his best to follow EPA regulations. It is illegal to modify or perforate your catalytic convertor in anyway. If you don't particularly care about EPA regs...then get a test pipe with a bung in it, by all means.

Further, I am not familiar with current HFC construction. I used to have a Random Technologies cat on my Buick and I ended up guttin it and just running the shell. Anyway, it was filled with this sort of dry fibrous substrate stuff. So, the O2 sensor if placed inside the cat would not be hangin freely in the exhaust stream.

Although, I am definitely not an engineer, I think that the cat alters the carbon and oxyen compounds present in your exhaust gas. What you're interested in are the number of O2 molecules/ unburned fuel molecules present before the catalytic converts(alters) the exhaust gas.

 

OK, here's my thoughts...

If you're ONLY replacing the stock catalyst on your IX with a HFC and you're keeping both the stock cat back exhaust and the stock downpipe in place then you have two options:

1.) You can have a bung welded in to your HFC in the short section of pipe right after the catalyst but before the flange. Obviously you'd want it after the catalyst material and not before as the goal of the second O2 sensor is to make sure your catalyst is working properly. HOWEVER, even though you have a catalyst, because a HFC is not necessarily as efficient as the stock cat and you may still get a SES light. I would recommend still using the spark plug anti-fouler fix for the second O2 sensor.

2.) There is a method using a certain resistor and changing some settings in the ECU (using a program file ECUFlash and the Tactrix USB OBDII cable) of disabling the second O2 sensor so that it can be disconnected and removed. In this case you wouldn't need a O2 bung at all.

IF you're going to be getting a cat back exhaust to go along with your HFC then your options are:

1.) Wait and find out if your cat back exhaust has an O2 bung already in it (both of mine did). Then use the spark plug anti-fouler fix to avoid an SES light.

2.) If you exhaust doesn't have the extra O2 bung in there, have one welded in OR use the ECUFlash/resistor fix to remove the second O2 sensor all together.

As per your questions...

1.) As I mentioned above, you COULD have an O2 bung welded in the short portion of pipe right after the catalyst but before the flange. But I think the best clearance under the car would be just at the beginning of the cat back and after the flange from the catalyst. I think this is why it is located here when installing a cat back exhaust.

2.) Yes, the stock catalyst has an indentation where the secondary O2 sensor is located. But on the stock catalyst the O2 sensor is located about half way through the catalyst. You wouldn't want to do this with your HFC because this would punch right into the catalyst material. So you can either have the O2 bung welded in the pipe at the very end of the HFC OR get a cat back exhaust with the bung already there.

Hope this helps!

 

Hey guys --

Thanks for the detailed follow-up. It's all crystal clear now!!!

RedAustinIX